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Changes in nutritive value of tall fescue hay as affected by natural rainfall and moisture concentration at baling
Animal Feed Science and Technology 109 (2003) 47–63
Changes in nutritive value of tall fescue hay as affected by natural rainfall and moisture concentration at baling夽 J.E. Turner a , W.K. Coblentz a,∗ , D.A. Scarbrough a , R.T. Rhein a , K.P. Coffey a , Z.B. Johnson a , C.F. Rosenkrans Jr. a , D.W. Kellogg a , J.V. Skinner Jr. b b
a Department of Animal Science, University of Arkansas, Fayetteville, AR 72701, USA Resident Director, Arkansas Agricultural Experiment Station, Fayetteville, AR 72701, USA
Received 16 January 2003; received in revised form 21 May 2003; accepted 29 May 2003
Abstract Relatively little is known about the combined effects of rain damage and spontaneous heating on the storage characteristics and nutritive value of tall fescue (Festuca arundinacea Schreb.) hay. Objectives were to assess effects of these variables in five management situations. ‘Kentucky 31’ tall fescue infested with the fungal endophyte (Neotyphodium coenophialum [Morgan-Jones & Glenn, Bacon, and Hamlin comb. nov.]) was packaged in conventional rectangular bales at 99 g/kg (low, L), 164 g/kg (ideal, I), and 225 g/kg (high, H) of moisture prior to rainfall, and at 246 g/kg of moisture after a 23 mm rainfall event (H–R) and at 93 g/kg of moisture after a total accumulation of 72 mm of rain (L–R). Concentrations of neutral-detergent fiber (NDF), acid-detergent fiber (ADF), and lignin immediately after baling increased (P ≤ 0.017) with rain damage, but concentrations of total N and fiber-associated N components were little affected. Immediately after baling, the in situ dry matter (DM) disappearance for L–R hay was 32–44 g/kg lower (P = 0.0001) than observed for hays baled without rain damage. After a 40–45-day storage period, L and I hays had a 31–36 g/kg advantage for in situ DM disappearance over hays damaged by spontaneous heating (H), rainfall (L–R), or both (H–R). Generally, the effects of a single 23 mm rainfall event on the nutritive value
Abbreviations: ADF, acid-detergent fiber; ADIN, acid-detergent insoluble N; DM, dry matter; HDD, heating degree days >30 ◦ C; H, high-moisture bales (225 g/kg of moisture); H–R, high-moisture, rain-damaged bales (246 g/kg of moisture; 23 mm of total rainfall); L, low-moisture bales (99 g/kg of moisture); L–R, low-moisture, rain-damaged bales (93 g/kg of moisture; 72 mm of total rainfall); I, ideal-moisture bales (164 g/kg of moisture); NDF, neutral-detergent fiber; NDIN, neutral-detergent insoluble N 夽 Contribution No. 01087 of the Arkansas Agricultural Experiment Station. ∗ Corresponding author. E-mail address: [email protected] (W.K. Coblentz). 0377-8401/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0377-8401(03)00209-8
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of tall fescue hay was relatively small, but damage increased substantially with multiple rainfall events. © 2003 Elsevier B.V. All rights reserved. Keywords: Tall fescue hay; Baling; Rainfall event
1. Introduction Tall fescue is the primary cool season grass forage in the eastern half of the United States (Sleper and Buckner, 1995). The primary area of its adaptation is the upper south, an area noted for high relative humidity and a high probability of rainfall events. The recommended growth stage for hay harvest is boot stage to early heading (Ball et al., 1996), which often coincides with a high probability of rainfall. For example, the expected monthly norms for rainfall in April, May, and June in Fayetteville (Arkansas, USA) are 110, 129, 134 mm, based on data compiled between 1971 and 2000 (National Oceanic and Atmospheric Administration, 2002). This can delay harvest, thereby decreasing nutritive value and subsequent animal performance. The alternative to delaying harvest is to subject fescue hay crops to a higher probability of rain damage. Effects of rainfall on nutritive value are well known for alfalfa (Medicago sativa L.), but limited information is available for most grasses. Rainfall events during forage wilting can reduce dry matter (DM) yields, and the possibility of losing the entire crop exists if rainfall persists for extended periods of time (Rotz and Abrams, 1988). Collins (1982) determined that nonstructural carbohydrates are a primary component of the DM leached from rain-damaged forage. This reduces the forage digestibility, while increasing concentrations of the fibrous components within the forage (Collins, 1982, 1983; Fonnesbeck et al., 1982; Rotz and Abrams, 1988). Some studies suggest that concentrations of N and minerals are minimally affected by rain damage (Collins, 1985), while other research indicates that concentrations of N may actually increase slightly after rainfall events (Rotz et al., 1991), because some N fractions are less soluble than other components of forage DM. High probabilities of rainfall may also persuade hay growers to package and store hay at concentrations of moisture that are greater than the 200 g/kg threshold level that is generally recommended for acceptable storage characteristics. Concentrations of moisture greater than 200 g/kg provide a favorable environment for growth of microorganisms in hays during storage. Typically, these microorganisms oxidize nonstructural carbohydrates preferentially for energy, and produce heat via respiration. Additional deleterious effects of spontaneous heating in forages include mold growth, increased concentrations of fiber, reduced digestibility, and nonenzymatic browning that can decrease bioavailability of N (Coblentz et al., 2000). Many investigations of rainfall effects on wilting forages have been conducted with legumes, but relatively little work has focused on the examination of these effects in grasses. Improved knowledge of effects of rainfall on wilting forages would be valuable to livestock and hay producers. The objective was to assess the influence of natural
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rainfall, baling moisture, and spontaneous heating on the nutritive value of tall fescue hay. 2. Materials and methods 2.1. Sample generation A well-established stand of endophyte-infested ‘Kentucky-31’ tall fescue was harvested when fully headed with a disc mower on 23 May 2000 at the University of Arkansas Forage Research Area in Fayetteville (36◦ 05 N; 94◦ 10 W; elevation 394.5 m). The mower did not include a conditioning device and forage used in this study was the initial spring growth. Fertilization consisted of 56 kg/ha N applied as ammonium nitrate on 25 February 2000. The initial harvest was mowed in three blocks of 10 swaths each and allowed to dry until 24 May, when the highest desired concentration of moisture was reached (Table 1). On this date, two swaths were raked together prior to baling at 08:30 h with a side-delivery rake. Raked double-rows in each block were randomly assigned to one of three moisture concentrations chosen to provide slightly higher than ideal (H), ideal (I), and lower (L) than ideal concentrations of moisture at baling (224, 164, and 99 g/kg, respectively). The H, I, and L treatments were all baled on 24 May. Ideal moisture was based on the 200 g/kg threshold for acceptable storage of conventional rectangular bales suggested by Collins et al. (1987). Paired swaths, selected randomly within each field block immediately after mowing, were purposely not raked. These swaths remained in the field after baling the three initial treatments (i.e., H, I, and L), thereby allowing the option of baling rain-damaged forage if weather conditions permitted. A 23 mm rainfall event occurred after baling was Table 1 Timeline for mowing, raking, and baling events as well as cumulative rainfall for each of the five tall fescue baling treatmentsa Date
Treatments mowed
23 May 24 May 25 May 26 May 27 May 28 May 29 May
H, I, L, H–R, L–R
a
Treatments baled
Raking time (h of day)
Precipitation (mm)
Cumulative precipitation prior to balingb (mm)
H, I, L
23d
0
H–R
08:30c 15:00e 08:00e
45f 4
23
L–R
11:00g
72
H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). b Total precipitation that fell prior to baling the treatments identified on that date. c Treatments H, I, and L were raked at 08:30 h. d Precipitation fell after baling of H, I, and L treatments was complete. e Treatments H–R and L–R were raked at these times. f Precipitation fell after baling of H–R treatment was complete. g Only treatment L–R was raked at this time.
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completed on 24 May. Rained-on swaths within each block were inverted at 15:00 h on 25 May to enhance drying. These swaths were raked together at 08:00 h on 26 May and baled at 10:00 h at a higher than ideal concentration of moisture (246 g/kg; H–R). A second 45 mm rainfall event began at 10:30 h the same day, which limited the H–R baling treatment to two replications. A third 4 mm rainfall event occurred the following day (27 May). On 28 May, swaths from the remaining forage were inverted and allowed to dry until 11:00 h the following day, when the final baling treatment was obtained at a low concentration of moisture (93 g/kg; L–R). The L–R treatment received a cumulative total of 72 mm of rainfall prior to baling. For each combination of moisture and field block, 12 conventional rectangular bales (average size = 0.48 m × 0.38 m × 0.93 m) were made with a New Holland Model 320 baler (Ford New Holland, Inc., New Holland, PA). The method of stacking the baling treatments was similar to that reported previously (Coblentz et al., 2000; Turner et al., 2002). Wooden pallets were placed on the floor of an open-air pole barn. Six bales from each group of 12 were placed side by side, strings up, on top of the wooden pallets. The remaining six bales from each replication were positioned in the same orientation on top of the first six bales, thereby creating stacks two bales high and six bales wide for each field replication of each treatment. Individual stacks containing 12 bales were surrounded on the sides and top by dry bales of wheat straw to limit effects of diurnal variations in ambient temperature. Stacks were created within approximately 2 h of baling. All bales were weighed and measured to determine bale density prior to storage. Core samples were taken from two bales within each replicate of 12 bales prior to stacking and at 4, 8, 12, 24 days post-baling using a Uni-Forage Sampler (Star Quality Samplers, Edmonton, AB, Canada) fitted to an electric drill. These sampling intervals were based on the original baling date and so sampling times did not occur on the same calendar date for each treatment. A final, post-storage, sampling date occurred on the same calendar date for all treatments, which was 45 days after baling for H, I, and L bales, 42 days after baling for H–R bales, and 40 days after baling for L–R bales. By the final sampling date, the internal bale temperatures of all bales had been ambient for at least 10 days. Bales were assigned randomly to one of the six sampling dates, and each pair of bales sampled on a given date contained one bale from both the top and bottom storage layers. Based on previous temperature vs. time in storage curves for other forages (Coblentz et al., 1996, 2000; Turner et al., 2002), these sampling dates were selected to approximately coincide with several key portions of a typical heating curve. These included: (i) the end of the initial heating period (day 4); (ii) the onset, peak, and end of the secondary heating phase (days 8, 12, and 24, respectively); and (iii) the end of the study (day 40 for L–R, day 42 for H–R, or day 45 for H, I, and L). The day 0 sampling date served as a pre-storage estimate of forage nutritive value. Eight core samples totaling between 60 and 120 g were taken from each bale (i.e., four cores per end). Bales were removed from each stack for sampling and then returned to their previous location in the stack for the remainder of the trial to maintain the integrity of the stack. All forage samples were dried under forced air at 55 ◦ C for 72 h. For bales sampled on day 0, this technique was used to estimate the initial concentration of moisture for each baling treatment. Recoveries of DM were determined from calculated DM weight of each bale before and after storage.
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Bales sampled after storage were visually appraised for mold growth by the method of Roberts et al. (1987) using a five point scale where: 1, no visible mold; 2, presence of spores between flakes; 3, presence of spores throughout the bale; 4, mycelial mat between flakes; and 5, mycelial mat throughout the bale. When appropriate, increments of 0.25 were used to evaluate each bale. 2.2. Temperature analysis Prior to stacking, bales assigned to the 24 days and post-storage sampling dates were fitted with single thermocouple wires inserted into the center of each bale. Bale temperatures were recorded twice daily at 06:30 and 15:00 h until all treatments had been in storage for 14 days and once daily at 15:00 h during the remainder of the storage period. Temperature data was collected with an Omega 450 AKT Type K thermocouple thermometer (Omega Engineering, Stamford, CT). The observed temperature was considered to be the mean internal bale temperature for a given day, except during the initial 14 days, when the mean of the two observations was used. For each day of storage, heating degree days >30 ◦ C (HDD) were calculated by subtracting 30 ◦ C from the mean internal bale temperature. These differences were then summed over the entire storage period. Therefore, HDD is a single number that represents both the magnitude and duration of heating in each bale. Other temperature-related response variables included maximum temperature, minimum temperature, and the average temperature over the entire storage period. 2.3. Chemical analysis of forage Dry forage samples were ground through a Wiley mill fitted with a 1 mm screen (Arthur H. Thomas, Philadelphia, PA) and subsequently analyzed for N, neutral-detergent fiber (NDF), acid-detergent fiber (ADF), lignin, neutral-detergent insoluble N (NDIN), and acid-detergent insoluble N (ADIN). The NDF, ADF, and lignin analyses were conducted using batch procedures outlined by ANKOM Technology Corp. (Fairport, NY). Sodium sulfite and heat-stable ␣-amylase were omitted from the NDF procedure. These methods have been described and subsequently compared to conventional methods by Vogel et al. (1999) and found to give comparable results. Similar agreement between conventionally filtered and filter-bag procedures also have been reported for NDF (Komarek, 1993) and ADF (Komarek et al., 1994). Both NDF and ADF are expressed with residual ash. Nitrogen was quantified by a modified Kjeldahl procedure (Kjeltech Auto 1030 Analyzer, Tecator, Inc. Herndon, VA); the N concentrations in NDF (NDIN) and ADF (ADIN) residues were determined by procedures identical to those used for total N, and reported on the basis of total DM and N. Procedures for determination of NDIN and ADIN were consistent with the guidelines established by Licitra et al. (1996) with the exception that the ANKOM filter-bag method was used for digestion of forages in neutral and acid detergent. 2.4. In situ analysis A ruminally cannulated crossbred steer weighing 481 kg was used to determine the disappearance of DM after a 48 h ruminal in situ incubation for bale samples obtained before
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and after storage. The University of Arkansas Institutional Animal Care and Use Committee approved surgical procedures and anesthesia for the cannulation and care of the steer. The single 48 h endpoint was utilized to determine relative rankings of in situ disappearance, not to estimate actual in vivo DM digestibility. In a review, Weiss (1994) noted that in most studies the in situ DM disappearance at 48 or 72 h was correlated to DM digestibility in vivo, and this experimental approach ranked forages fairly consistently with in vivo data. Only a single steer was needed because duplicate bags of all field replications easily could be incubated within the same animal. The steer was housed in an individual 3.4 m × 4.9 m pen with a concrete floor that was cleaned regularly, and it was offered an alfalfa hay-based diet at a maintenance energy level of intake (i.e., 1.15% of body weight) throughout the trial (Vanzant et al., 1998). The ration contained 90% alfalfa hay (30.4 g/kg N, 444 g/kg NDF) and 10% corn grain-based supplement (983 g/kg cracked corn, 0.17 g/kg liquid molasses, 13.4 g/kg trace mineral salt, 0.9 g/kg Vitamins A, D, E premix, 1.3 g/kg Vitamin E premix, and 1.1 g/kg Rumensin 80® (176 mg/g monensin; Elanco Animal Health, Indianapolis, IN)). The steer had ad libitum access to water throughout the trial. The diet was offered in equal portions at 06:30 and 16:30 h, and the steer was adapted to the basal diet for 10 days prior to initiating the trial. Dacron bags (10 cm × 20 cm; 53 ± 10 mm pore size; Ankom Technology Corp., Fairport, NY) were filled with 5 g of dried forage that had been ground through a 1 mm screen in a Wiley mill. Dacron bags were heat-sealed using an impulse sealer (Model CD-200; National Instrument Co. Inc., Baltimore, MD). Duplicate bags were placed in a 36 cm × 50 cm mesh bag. Four mesh bags each containing 28 dacron bags (total of 112) were placed in the ventral rumen prior to the 06:30 h feeding and incubated for 48 h. Following incubation, all dacron bags were subjected to 10 cold-water rinse cycles in a commercial, top-loading washing machine (Model LXR7144EQ1, Whirlpool Corp., Benton Harbor, MI). Rinse cycles consisted of a 1 min agitation and a 2 min spin per rinse cycle (Coblentz et al., 1997; Vanzant et al., 1998). Rinsed dacron bags were dried to a constant weight at 50 ◦ C and allowed to equilibrate with air before analysis for residual DM (Vanzant et al., 1996). In situ disappearance was calculated as the proportion of forage DM that disappeared from the dacron bags during the 48 h ruminal incubation. 2.5. Statistical analysis Moisture concentration, bale measurements, and their associated storage characteristics were analyzed as a randomized incomplete block design by PROC GLM of SAS (1990). Four treatments (H, I, L, and L–R) contained three field replications, while treatment H–R had two. Single degree-of-freedom contrasts were used to compare least-square means for both initial bale characteristics and storage characteristics. A similar approach was used to evaluate indices of nutritive value prior to storage (day 0) and after storage by independent analyses of variance. In this study, bales were sampled on six dates throughout the storage period, and indices of nutritive value were evaluated for each of these sampling dates. In addition to the analyses of nutritive value described for pre- and post-storage hays, changes over time in storage were evaluated using storage time as a continuous variable. Initially, our model included linear, quadratic, cubic, and quartic effects, but these terms frequently interacted (P < 0.05)
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with baling treatment. Therefore, the response over storage time for each baling treatment was evaluated independently using PROC REG of SAS (1990). When the highest order term for storage time (i.e., quartic, cubic, quadratic, or linear) was not significant (i.e., P > 0.05), it was removed from the model and the data was re-analyzed. This was repeated until the highest order term remaining in the model was significant (P < 0.05). Throughout all aspects of the study, statistical significance was declared at P < 0.05; while potential trends of importance to the discussion and explanation of the results were identified at the P < 0.10 level of confidence. 3. Results and discussion 3.1. Bale characteristics Bale characteristics were affected by the concentration of moisture in the forage at the time of baling (Table 2). Bale length was longer (P = 0.003) by 0.03–0.06 m for hays baled under the 200 g/kg moisture threshold for acceptable storage (Collins et al., 1987), than for hays baled at concentrations of moisture that exceeded this threshold. This was true for hays that did not receive rain prior to baling (P = 0.018) and for hays receiving rainfall prior to baling (P = 0.003). Despite these differences in bale length, bale volume was not affected. As expected, bale weight and density on both a wet and dry basis were greater for H and H–R bales compared to those baled at acceptable concentrations of moisture (P ≤ 0.0004). This also was true within the more limited context of hays receiving no rain damage (P ≤ 0.002), and for hays damaged by rain (P ≤ 0.003). Generally, bale densities observed in this study, which ranged from 114 to 211 kg/m3 on an as-is basis, were comparable to those reported for bermudagrass hays made at similar moisture concentrations with the same haying equipment (Coblentz et al., 2000). 3.2. Temperature responses Internal bale temperature vs. time curves for selected baling treatments are shown in Fig. 1. The responses of the H and H–R bales were similar to those exhibited by both alfalfa and bermudagrass packaged at moisture concentrations greater than 200 g/kg (Coblentz et al., 1997, 2000; Turner et al., 2002), while the I, L, and L–R bales exhibited minimal heating responses. The sharp decline in internal bale temperatures between 12 and 15 days of storage was the result of relatively low overnight ambient temperatures that approached 10 ◦ C. It is likely that these relatively low ambient temperatures inhibited spontaneous heating within these hays. For example, Rees (1982) has indicated that growth of microorganisms in hay is often restricted when internal bale temperatures fall below 20 ◦ C. The HDD accumulated during the storage period were greater (P < 0.0001) for H and H–R bales than for bales packaged at concentrations of moisture <200 g/kg (Table 2). Despite its higher concentration of moisture at baling, the H–R bales accumulated fewer (P = 0.028) HDD than H bales. This could have occurred because nonstructural carbohydrates were leached from the H–R hay, thereby reducing the pool of available sugars that could potentially support spontaneous heating. However, a simpler explanation may
54
Moisture content (g/kg) Treatmentc H I L H–R L–R S.E.d
225 164 99 246 93 5
Contrastse (P > F) 1 <0.0001 2 <0.0001 3 <0.0001 4 0.009
Bale length (m)
Bale volume (m3 )
0.90 0.91 0.94 0.91 0.96 0.01
0.167 0.167 0.173 0.170 0.177 0.004
34.8 26.6 22.6 31.2 20.1 1.5
211 160 131 186 114 10
0.003 0.018 0.003 0.311
0.194 0.374 0.171 0.550
<0.0001 0.0002 0.001 0.085
<0.0001 0.0001 0.001 0.057
Bale weight (as-is) (kg)
Bale density (as-is) (kg/m3 )
Bale weight (DM basis) (kg)
Bale density (DM basis) (kg/m3 )
27.0 22.3 20.4 25.4 18.4 1.2
164 134 118 151 104 7
0.0004 0.002 0.003 0.251
0.0002 0.001 0.001 0.170
HDD
MAX (◦ C)
163 32 14 129 5 10
49.8 40.0 42.8 50.8 31.4 1.3
<0.0001 <0.0001 <0.0001 0.028
<0.0001 0.0002 <0.0001 0.658
Visible moldb
DM recovery (g/kg)
31.2 27.7 24.8 29.8 24.8 0.3
1.75 1.08 1.00 1.71 1.04 0.28
934 965 981 959 947 23
<0.0001 <0.0001 <0.0001 0.006
0.017 0.032 0.114 0.847
AVG (◦ C)
0.413 0.122 0.597 0.350
HDD, heating degree days >30 ◦ C; MAX, maximum internal bale temperature; and 40-day AVG, average internal bale temperature over the entire 40-day storage period. Visible mold assessment score: 1, no visible mold; 2, presence of spores between flakes; 3, presence of spores throughout the bale; 4, mycelial mat between flakes; and 5, mycelial mat throughout the bale (Roberts et al., 1987). c H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). d Standard error of the mean for the H–R treatment with n = 2 replications. Other treatments had n = 3 replications. e 1: all high moisture (H, H–R) vs. all low moisture (I, L, L–R); 2: high moisture (H) vs. low moisture (I, L) without rain; 3: high moisture (H–R) vs. low moisture (L–R) with rain; and 4: high moisture without rain (H) vs. high moisture with rain (H–R). a
b
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Table 2 Bale characteristics of tall fescue hay made at five concentrations of moisture and with or without natural rainfalla
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55 50
Temperatue,˚C
45 40 35 30 25 20 15 0
5
10
15
20
25
Fig. 1. Internal bale temperature during the initial 25 days of bale storage for three baling treatments (S.E. = 1.9 ◦ C) of tall fescue hay: H (䊐, 225 g/kg moisture, no rain); I (䊏, 164 g/kg moisture, no rain); and H–R (䊉, 246 g/kg moisture, 23 mm rain).
be that the H–R treatment had a 2-day shorter interval of time in storage prior to the onset of relatively cooler weather. In a pattern similar to that observed for HDD, the average, minimum, and maximum internal bale temperatures were higher for H and H–R bales than for those packaged at <200 g/kg of moisture. The H bales exhibited a higher (P = 0.006) average internal bale temperature than did H–R bales, but this was not related to maximum temperature, which did not differ between the two treatments. Visible mold score (Table 2) was higher (P = 0.017) for H and H–R hays compared to the other drier hays (I, L, L–R). This difference was also observed within hays receiving no rain damage prior to baling and H bales had a higher (P = 0.032) visual mold score than I and L. However, for rain-damaged hays, H–R bales did not differ from the L–R or H bales. Generally, the low visible mold scores, which did not exceed 1.75 for any treatment, can be explained on the basis of the low overnight temperatures that occurred between 12 and 15 days of storage and the comparatively low concentrations of moisture in these bales at baling. The DM recovery did not include field losses associated with rainfall events, because DM recovery was determined from the DM weight of each bale immediately prior to storage and after the storage period of approximately 6 weeks. No contrasts differed. 3.3. Nutritive value prior to storage The concentrations of fiber components and the in situ 48 h DM disappearance for the five baling treatments sampled immediately after baling (day 0) are in Table 3. There was no difference between I and L for any of these response variables, providing little evidence of leaf shatter in the driest (L) forage, and any extra wilting time used by growers to attain excessively low-moisture levels serves little practical purpose with small rectangular bales. However, it remains unclear whether these observations are true for large round bale
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Table 3 Concentrations of fiber and nitrogen components and 48 h in situ DM disappearance for tall fescue hay sampled immediately after baling (day 0)a NDF (g/kg)
ADF (g/kg)
Baling treatmentc H 663 I 677 L 673 H–R 720 L–R 764 3 S.E.d
376 383 381 405 426 3
Contrastse 1 2 3 4
0.0001 <0.0001 0.001 0.476
(P > F) <0.0001 <0.0001 <0.0001 0.348
Lignin (g/kg)
DM N disappearanceb (g/kg) (g/kg)
NDIN ADIN NDIN ADIN (g/kg) (g/kg) (g/kg N) (g/kg N)
48.1 51.2 49.8 54.8 55.2 1.5
641 629 639 618 597 9
2.27 2.37 1.87 2.44 2.60 0.20
0.87 1.07 1.00 1.04 1.07 0.05
0.164 0.020 0.447 0.025
0.345 0.110 0.682 0.300
0.017 0.005 0.847 0.413
0.075 0.0001 0.088 0.297
12.6 13.1 12.7 13.5 13.7 0.5 0.232 0.088 0.784 0.476
179 180 147 182 192 12 0.369 0.081 0.554 0.047
70.7 82.5 79.9 76.6 78.4 4.6 0.835 0.880 0.774 0.628
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; N, nitrogen; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b DM disappearance measured by incubating forages for 48 h in situ. c H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). d Standard error of the mean for the H–R treatment with n = 2 replications. Other treatments had n = 3 replications. e 1: one rainfall event (H–R) vs. no rain (H, I, L); 2: multiple rainfall events (L–R) vs. no rain (H, I, L); 3: single rainfall event (H–R) vs. multiple rainfall events (L–R); and 4: ideal moisture (I) vs. excessively dry (L).
packages. Concentrations of NDF, ADF, and lignin increased as the forage was exposed to rainfall events. This was not an unexpected result since others (e.g., Collins, 1982, 1983, 1985; Rotz and Abrams, 1988; Rotz et al., 1991) have reported an increase in concentrations of fiber components in response to rain damage. Contrasts of H–R hay with hays receiving no rain damage (H, I, and L) were significant (P ≤ 0.017) for each of the response variables. Contrasts of forage receiving 72 mm of cumulative rainfall prior to baling (L–R) with hays receiving no rain damage also were highly significant (P ≤ 0.005) for these fiber components. For NDF and ADF, H–R and L–R hays differed (P ≤ 0.001), but this response was not observed for lignin (P = 0.847). Generally, L–R bales exhibited the greatest increases in NDF and ADF concentrations. Respective increases of these fiber components were 101 and 50 g/kg relative to those measured for H bales. For H–R bales, increases in NDF and ADF were approximately half (57 and 29 g/kg, respectively) those observed for L–R bales. Clearly, these responses reflect the differences in cumulative rainfall prior to baling for the H–R and L–R treatments. The higher concentrations of fiber in the H–R and L–R hays are likely an indirect result of leaching, and prolonged or reactivated respiration of nonstructural carbohydrates, not actual accumulation of additional fiber (Collins, 1982). Pre-storage in situ DM disappearance after a 48 h ruminal incubation (Table 3) was higher (P = 0.0001) for baling treatments that were not exposed to rainfall (629–641 g/kg) than
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for the L–R baling treatment (597 g/kg). In situ DM disappearance for the H–R baling treatment (618 g/kg) was intermediate between hays receiving no rain damage and L–R hay, and only tended (P = 0.075 and 0.088, respectively) to differ from each. Generally, a single 23 mm rainfall event depressed in situ DM disappearance by only 11–23 g/kg, which is likely to have little biological significance. Generally, contrasts evaluating N components in baling treatments prior to storage were not significant, indicating little effect of rainfall on these hays. Concentrations of NDIN (g/kg DM) for L–R bales were higher (P = 0.020) than observed in hays receiving no rain damage. There were tendencies (P ≤ 0.088) for total N and NDIN (g/kg N) to differ between L–R hay and treatments receiving no rain damage, but these tendencies were not observed when hays receiving no rain damage were compared with H–R hay. There were no differences between H–R and L–R hays for any N-related response variable. Concentrations of NDIN (g/kg N) differed (P = 0.047) between I and L treatments, indicating there was a response to excessive dessication, but the lower concentration of NDIN in L hay would not be consistent with increased leaf shatter and the reasons for this observation remain unclear. 3.4. Comparisons of hays after storage Comparisons of nutritive value for treatment hays sampled after a storage period of approximately 6 weeks (Table 4) are probably the most meaningful for livestock and hay producers. Concentrations of NDF and ADF in hays damaged by natural rainfall, spontaneous heating during storage, or both (H, H–R, and L–R) were greater (P < 0.0001) than observed for undamaged hays (I, L). Similarly, concentrations of NDF and ADF were higher (P ≤ 0.0002) in rain-damaged hays (H–R, L–R) than in hays receiving no rain prior to storage (H, I, L), and also were higher (P ≤ 0.001) in hays that heated spontaneously (H, H–R) vs. hays that incurred minimal or no heating during storage (I, L, L–R). The concentration of NDF in H–R bales was higher (P = 0.003) by 40 g/kg than in H bales that also heated, but received no rain damage. However, there were no differences (P = 0.195) in concentrations of ADF between H–R and H bales. After storage, concentrations of lignin were relatively consistent across treatments. There was a tendency (P = 0.058) for rain-damaged hays to have higher concentrations of lignin than hays receiving no rainfall prior to storage. However, all other contrasts were not significant. The I and L baling treatments had higher (P < 0.0001) post-storage in situ DM disappearance than the other baling treatments that incurred rain damage, spontaneous heating, or both. This can probably be explained on the basis of better conservation of nonstructural carbohydrates in the absence of rain damage and spontaneous heating. After the 40–45-day storage period, in situ DM disappearance of H, H–R, and L–R bales were virtually identical, and ranged from 31 to 35 g/kg less than the I and L treatments. After storage, hays that incurred spontaneous heating (H and H–R) had a tendency (P = 0.069) for higher concentrations of total N than hays with minimal spontaneous heating (Table 4). High-moisture hays that lose carbohydrates via respiration during storage are known to exhibit slight increases in total N in the short term (<60 days; Rotz and Muck, 1994). For damaged hays that incurred spontaneous heating, rain damage, or both, NDIN and ADIN concentrations were higher (P ≤ 0.001) than observed in undamaged hays. Elevated concentrations of NDIN and ADIN also were observed in comparisons of rain-damaged
58
NDF (g/kg)
ADF (g/kg)
Baling treatmentc H 745 I 705 L 681 H–R 785 L–R 760 7.1 S.E.d
434 411 397 444 440 5.1
Contrastse (P > F) 1 <0.0001 2 <0.0001 3 <0.0001 4 0.003
<0.0001 0.0002 0.001 0.195
a
Lignin (g/kg) 58.9 62.0 58.3 64.7 68.3 3.86 0.224 0.058 0.731 0.270
DM disappearanceb (g/kg) 598 629 632 596 597 7.5 <0.0001 0.001 0.001 0.866
N (g/kg)
14.3 13.1 12.7 13.7 12.3 0.7 0.372 0.592 0.069 0.575
NDIN (g/kg)
ADIN (g/kg)
3.63 2.47 1.93 3.59 2.43 0.16
1.47 0.83 0.93 2.10 1.57 0.12
<0.0001 0.028 <0.0001 0.838
<0.0001 <0.0001 0.0001 0.003
NDIN (g/kg N)
ADIN (g/kg N)
255 189 153 260 199 16
104.4 63.8 75.8 155.0 130.3 12.0
0.001 0.042 0.0004 0.826
0.0003 0.0004 0.005 0.015
NDF, neutral-detergent fiber; ADF, acid-detergent fiber; N, nitrogen; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. DM disappearance measured by incubating forages for 48 h in situ. c H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). d Standard error of the mean for the H–R treatment with n = 2 replications. Other treatments had n = 3 replications. e 1, all damaged hays (H, H–R, L–R) vs. no damage (I, L); 2, rain-damaged (H–R, L–R) vs. no rain (H, I, L); 3, spontaneous heating (H, H–R) vs. minimal heating (I, L, L–R); and 4, spontaneous heating and rain (H–R) vs. heating only (H). b
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Table 4 Concentrations of fiber and nitrogen components and 48 h in situ DM disappearance for tall fescue hay sampled after a storage period of approximately 6 weeksa
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hays with hays receiving no rain prior to baling (P ≤ 0.042), and for comparisons of hays that heated spontaneously with those that did not (P ≤ 0.005). In addition, these relationships were observed when NDIN or ADIN was expressed as a proportion of total plant DM or N. Concentrations of NDIN in H–R bales did not differ (P ≥ 0.826) from those found in H bales, but ADIN was higher (P ≤ 0.015) in H–R bales than in H bales that heated without previous rain damage during wilting. 3.5. Changes in nutritive value during storage In this study, bales were sampled on six dates throughout the storage period so that indices of nutritive value could be evaluated as a function of time in storage. Initially, there were numerous interactions (P < 0.05) of baling treatment with linear, quadratic, cubic, or quartic terms for storage time. Because of these interactions, relationships between indices of nutritive value and storage time were established for each individual baling treatment. Generally, changes in nutritive value due to time in storage were most obvious in bales that heated spontaneously (H and H–R; Tables 5 and 6, respectively). For treatments that incurred minimal spontaneous heating (I, L, and L–R), responses over time generally were static. Any regressions that were significant (P < 0.05) for these baling treatments tended to have narrow ranges of response over the storage period. For this reason, only data for Table 5 Regressions of concentrations of total N, fiber components, and N components on storage time for tall fescue hay baled at 225 g/kg of moisture without rainfall (H) and stored for approximately 6 weeksa Sampling date (days)
N (g/kg)
0 4 8 12 24 45 S.E.b
12.5 13.8 13.5 13.0 13.9 14.3 0.4
Modelc P > Fd
Linear 0.036
NDF (g/kg) 663 695 716 720 734 745 5 Cubic <0.0001
Coefficients Quartic Cubic Quadratic Linear
– – – 0.0291
– 0.00388 −0.317 8.19
RMSEe R2
0.82 0.246
10.3 0.897
ADF (g/kg) 376 387 402 408 397 434 4 Cubic <0.0001
Lignin (g/kg) 48.1 51.1 60.1 54.3 57.9 58.9 2.1 Quadratic 0.004
NDIN (g/kg N) 179 190 272 281 255 255 12 Cubic 0.003
ADIN (g/kg N) 70.7 64.3 83.9 91.9 105.7 104.4 7.4 Quadratic 0.001
– 0.00452 −0.296 5.53
– – −0.0102 0.652
– 0.0103 −0.803 17.2
– – −0.0371 2.56
7.16 0.890
3.53 0.528
31.7 0.628
13.4 0.598
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b Standard error of the baling treatment × sampling date interaction mean. c Best fit quartic, cubic, quadratic, or linear regression model. d F-test for regression model. e Root mean square error for the regression.
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Table 6 Regressions of concentrations of total N, fiber components, and N components on storage time for tall fescue hay baled at 246 g/kg of moisture after a single rainfall event of 23 mm (H–R) and stored for approximately 6 weeksa Sampling date (days)
N (g/kg)
0 4 8 12 24 42
13.4 13.4 12.9 13.9 13.5 13.7 0.5
S.E.b
NDF (g/kg)
ADF (g/kg)
Lignin (g/kg)
NDIN (g/kg N)
ADIN (g/kg N)
719 734 761 758 770 787
404 404 431 427 437 445
54.6 58.1 63.6 61.6 56.3 64.7
184 268 292 271 247 261
75.7 89.2 118.5 138.4 136.9 161.6
6
5
2.5
14
9.1
Quartic 0.001
Cubic 0.0001
Modelc
nsd
P > Fe
–
Cubic 0.0001
Linear 0.001
ns –
Coefficients Quartic Cubic Quadratic Linear
– – – –
– 0.0034 −0.256 6.31
– – – 0.946
– – – –
−0.00154 0.132 −3.59 34.2
– 0.00469 −0.349 8.54
RMSEf R2
– –
8.3 0.915
10.3 0.673
– –
12.7 0.924
11.0 0.913
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b Standard error of the baling treatment × sampling date interaction mean. c Best fit quartic, cubic, quadratic, or linear regression model. d Highest order independent term had a nonsignificant (P > 0.05) coefficient for quartic, cubic, quadratic and linear regressions. e F-test for regression model. f Root mean square error for the regression.
bales packaged at the ideal concentration of moisture (I) are presented to illustrate changes in nutritive value for bales that did not heat spontaneously (Table 7). One exception to this generalization was the concentration of ADIN in L–R bales, which increased quadratically (P = 0.001; R2 = 0.603) on a DM basis from 1.07 to 1.67 g/kg between days 0 and 12 of storage before declining slightly to 1.57 g/kg by the final sampling date (data not shown). Similarly, ADIN (g/kg N) increased linearly (P = 0.002; R2 = 0.479) from 78.4 to 130.3 g/kg N during storage (data not shown). The quartic model for I bales (P = 0.002; R2 = 0.720; Table 7) describing the relationship between ADIN (g/kg N) and storage time is equally difficult to explain. Both NDIN and ADIN should increase in response to spontaneous heating as this process occurs via nonenzymatic browning or Maillard reactions, and because these fiber-associated N components are not affected by microbial respiration or volatilization of ammonia and other N compounds during storage (Rotz and Muck, 1994). However, it remains unclear why rain damage profoundly affected concentrations of ADIN after storage. Concentrations of water insoluble N components, such as ADIN, are known to increase in response to rain damage (Rotz and Muck, 1994). However, this was not observed for ADIN in our bales sampled on day 0 (P ≥ 0.110;
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Table 7 Regressions of concentrations of total N, fiber components, and N components on storage time for tall fescue hay baled at 164 g/kg of moisture without rainfall (I) and stored for approximately 6 weeksa Sampling date (days)
N (g/kg)
NDF (g/kg)
0 4 8 12 24 45
13.1 13.2 13.0 13.1 13.3 13.1
677 667 677 688 693 705
0.4
5
S.E.b
ADF (g/kg)
Lignin (g/kg)
NDIN (g/kg N)
ADIN (g/kg N)
383 391 387 384 388 411
51.2 51.0 53.9 51.3 57.8 62.0
180 166 196 177 174 189
82.5 100.4 67.8 68.6 101.9 63.8
4
2.1
12
7.4
Modelc
nsd
P > Fe
–
Linear 0.0003
Coefficients Quartic Cubic Quadratic Linear
– – – –
– – – 0.754
– – 0.0204 −0.399
– – – 0.258
– – – –
−0.00103 0.0752 −1.46 6.68
RMSEf R2
– –
10.5 0.574
6.76 0.681
3.28 0.616
– –
10.5 0.72
Quadratic 0.0002
Linear 0.0001
ns –
Quartic 0.002
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b Standard error of the baling treatment × sampling date interaction mean. c Best fit quartic, cubic, quadratic, or linear regression model. d Highest order independent term had a nonsignificant (P > 0.05) coefficient for quartic, cubic, quadratic and linear regressions. e F-test for regression model. f Root mean square error for the regression.
Table 5). It is also unclear why the concentration of ADIN in L–R bales increased from 78.4 to 130.3 g/kg N during a 40-day storage period where the maximum internal bale temperature reached 31.4 ◦ C and only 5 HDD were accumulated. In contrast, rain damage affected concentrations of NDIN prior to storage. Higher (P = 0.020; Table 3) concentrations of NDIN (g/kg DM) were observed on day 0 for L–R bales receiving multiple rainfall events than in hays receiving no rain prior to baling, and a similar tendency (P = 0.081) was observed when NDIN was expressed as a proportion of total N. The best fit models for H and H–R bales (Tables 5 and 6) generally were nonlinear, which agrees with past work (Turner et al., 2002) indicating that concentrations of fiber components, NDIN, and ADIN in bermudagrass increase rapidly with the onset of microbial respiration, but then stabilize after 2–3 weeks of storage. For H bales, concentrations of total N increased linearly (P = 0.036; R2 = 0.246; Table 5) during storage, but this relationship was not observed (P = 0.473) in H–R bales. For H bales, the relationship between total N and storage time was weaker than observed for NDF, ADF, lignin, and NDIN, and ADIN expressed as a proportion of total N (P ≤ 0.004; R2 ≥ 0.528). Cubic models were especially effective in explaining the relationship between both NDF and
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ADF and storage time (P < 0.0001; R2 ≥ 0.890). For H–R bales, there was no relationship (P > 0.339) between N or lignin and storage time. However, cubic models were especially effective (P = 0.0001; R2 ≥ 0.913) at explaining this relationship for NDF and ADIN (g/kg N), while quartic models provided the best fit (P = 0.001; R2 = 0.924) for NDIN (g/kg N).
4. Conclusions Before storage, tall fescue hay exposed to rainfall had higher concentrations of NDF and ADF than hay not exposed to rainfall. Generally, total N and N components only were affected marginally in hay that was exposed to rainfall. Immediately after baling, in situ DM disappearance was reduced by 32–44 g/kg in hay that was exposed to 72 mm of rainfall, relative to hays that were not damaged by rain. Intermediate reductions in ruminal DM disappearance were observed for hay receiving 23 mm of rainfall prior to baling. Generally, changes in nutritive value in response to spontaneous heating were small because no hay was baled at >250 g/kg of moisture, but the maximum changes in nutritive value occurred in hays that exhibited measurable spontaneous heating. Ball et al. (1996) has described the drastic increases in NDF and concurrent decreases in digestibility that occur when tall fescue matures past late-boot stage. By comparison, the effects of a single 23 mm rainfall event appear to be relatively minor. However, some caution is advised in interpretation of these results. The two rain-damaged baling treatments received rain in different amounts and frequencies, were baled at different moisture levels, and remained in the windrow different intervals of time prior to baling. Therefore, factors other than the actual amount of rainfall received during wilting may have influenced the results, particularly in samples obtained immediately after baling before any spontaneous heating may have occurred. Generally, our findings suggest that producers could benefit from pursuing harvest more aggressively, even when there is some chance of rain before the crop is dry. However, these studies do not consider potential effects on palatability and subsequent intake by cattle.
References Ball, D.M., Hoveland, C.S., Lacefield, G.D., 1996. Southern Forages, 2nd ed. Potash and Phosphate Institute and the Foundation for Agronomic Research, Norcross, GA. Coblentz, W.K., Fritz, J.O., Bolsen, K.K., Cochran, R.C., 1996. Quality changes in alfalfa hay during storage in bales. J. Dairy Sci. 79, 873–885. Coblentz, W.K., Fritz, J.O., Cochran, R.C., Rooney, W.L., Bolsen, K.K., 1997. Protein degradation responses to spontaneous heating in alfalfa hay by in situ and ficin methods. J. Dairy Sci. 80, 700–713. Coblentz, W.K., Turner, J.E., Scarbrough, D.A., Lesmeister, K.E., Johnson, Z.B., Kellogg, D.W., Coffey, K.P., McBeth, L.J., Weyers, J.S., 2000. Storage characteristics and nutritive value changes in bermudagrass hay as affected by moisture content and density of rectangular bales. Crop Sci. 40, 1375–1383. Collins, M., 1982. The influence of wetting on the composition of alfalfa, red clover, and birdsfoot trefoil hay. Agron. J. 74, 1041–1044. Collins, M., 1983. Wetting and maturity effects on the yield and quality of legume hay. Agron. J. 75, 523–527. Collins, M., 1985. Wetting effects on the yield and quality of legume and legume-grass hays. Agron. J. 77, 936–941.
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Collins, M., Paulson, W.H., Finner, M.F., Jorgenson, N.A., Keuler, C.R., 1987. Moisture and storage effects on dry matter and quality losses of alfalfa in round bales. Trans. ASAE 30, 913–917. Fonnesbeck, P.V., Garcia de Hernandez, M.M., Kaykay, J.M., Saiaday, M.Y., 1982. Estimating yield and nutrient losses due to rainfall on field-drying alfalfa hay. Anim. Feed Sci. Technol. 16, 7–15. Komarek, A.R., 1993. A filter bag procedure for improving efficiency of fiber analysis. J. Dairy Sci. 76 (Supplement 1), 250. Komarek, A.R., Robertson, J.B., Van Soest, P.J., 1994. A comparison of methods for determining ADF using the filter bag technique versus conventional filtration. J. Dairy Sci. 77 (Supplement 1), 114. Licitra, G., Hernandez, T.M., Van Soest, P.J., 1996. Standardization of procedures for nitrogen fractionation of ruminant feeds. Anim. Feed Sci. Technol. 57, 347–358. National Oceanic and Atmospheric Administration, 2002. Monthly station normals of temperature, precipitation, and heating and cooling degree days 1971–2000. Climatography of the United States No. 81.03 Arkansas. National Climatic Data Center, NESDIS, NOAA, Asheville, NC. Rees, D.V.H., 1982. A discussion of sources of dry matter loss during the process of haymaking. J. Agric. Eng. Res. 27, 469–479. Roberts, C.A., Moore, K.J., Graffis, D.W., Kirby, H.W., Walgenbach, R.P., 1987. Chitin as an estimate of mold in hay. Crop Sci. 27, 783–785. Rotz, C.A., Abrams, S.M., 1988. Losses and quality changes during alfalfa hay harvest and storage. Trans. ASAE 31, 350–355. Rotz, C.A., Muck, R.E., 1994. Changes in forage quality during harvest and storage. In: Fahey, G.C., et al. (Eds.) Forage Quality, Evaluation, and Utilization. Proceedings of the National Conference on Forage Quality, Evaluation, and Utilization. University of Nebraska, Lincoln, 13–15 April 1994. ASA, CSSA, and SSSA, Madison, WI, pp. 828–868. Rotz, C.A., Davis, R.J., Abrams, S.M., 1991. Influence of rain and crop characteristics on alfalfa damage. Trans. ASAE 34, 1583–1591. SAS, 1990. SAS/STAT: User’s Guide, Version 6, 4th ed. SAS Institute, Cary, NC. Sleper, D.A., Buckner, R.C., 1995. The fescues. In: Barnes, R.F., et al. (Eds.), Forages: The Science of Grassland Agriculture, vol. 1. Iowa State University Press. Ames, IA, pp. 345–356. Turner, J.E., Coblentz, W.K., Scarbrough, D.A., Coffey, K.P., Kellogg, D.W., McBeth, L.J., Rhein, R.T., 2002. Changes in nutritive value of bermudagrass hay during storage. Agron. J. 94, 109–117. Vanzant, E.S., Cochran, R.C., Titgemeyer, E.C., Stafford, S.D., Olsen, K.C., St. Jean, G., 1996. In vivo and in situ measurements of forage protein degradation in cattle. J. Anim. Sci. 74, 2773–2784. Vanzant, E.S., Cochran, R.C., Titgemeyer, E.C., 1998. Standardization of in situ techniques for ruminant feedstuff evaluation. J. Anim. Sci. 76, 2717–2729. Vogel, K.P., Pedersen, J.E., Masterson, S.D., Toy, J.J., 1999. Evaluation of a filter bag system for NDF, ADF, and IVDMD forage analysis. Crop Sci. 39, 276–279. Weiss, W.P., 1994. Estimation of digestibility of forages by laboratory methods. In: Fahey, G.C., et al. (Eds.), Forage Quality, Evaluation, and Utilization. Proceedings of the National Conference on Forage Quality, Evaluation, and Utilization. University of Nebraska, Lincoln, 13–15 April 1994. ASA, CSSA, and SSSA, Madison, WI, pp. 644–681.
Changes in nutritive value of tall fescue hay as affected by natural rainfall and moisture concentration at baling夽 J.E. Turner a , W.K. Coblentz a,∗ , D.A. Scarbrough a , R.T. Rhein a , K.P. Coffey a , Z.B. Johnson a , C.F. Rosenkrans Jr. a , D.W. Kellogg a , J.V. Skinner Jr. b b
a Department of Animal Science, University of Arkansas, Fayetteville, AR 72701, USA Resident Director, Arkansas Agricultural Experiment Station, Fayetteville, AR 72701, USA
Received 16 January 2003; received in revised form 21 May 2003; accepted 29 May 2003
Abstract Relatively little is known about the combined effects of rain damage and spontaneous heating on the storage characteristics and nutritive value of tall fescue (Festuca arundinacea Schreb.) hay. Objectives were to assess effects of these variables in five management situations. ‘Kentucky 31’ tall fescue infested with the fungal endophyte (Neotyphodium coenophialum [Morgan-Jones & Glenn, Bacon, and Hamlin comb. nov.]) was packaged in conventional rectangular bales at 99 g/kg (low, L), 164 g/kg (ideal, I), and 225 g/kg (high, H) of moisture prior to rainfall, and at 246 g/kg of moisture after a 23 mm rainfall event (H–R) and at 93 g/kg of moisture after a total accumulation of 72 mm of rain (L–R). Concentrations of neutral-detergent fiber (NDF), acid-detergent fiber (ADF), and lignin immediately after baling increased (P ≤ 0.017) with rain damage, but concentrations of total N and fiber-associated N components were little affected. Immediately after baling, the in situ dry matter (DM) disappearance for L–R hay was 32–44 g/kg lower (P = 0.0001) than observed for hays baled without rain damage. After a 40–45-day storage period, L and I hays had a 31–36 g/kg advantage for in situ DM disappearance over hays damaged by spontaneous heating (H), rainfall (L–R), or both (H–R). Generally, the effects of a single 23 mm rainfall event on the nutritive value
Abbreviations: ADF, acid-detergent fiber; ADIN, acid-detergent insoluble N; DM, dry matter; HDD, heating degree days >30 ◦ C; H, high-moisture bales (225 g/kg of moisture); H–R, high-moisture, rain-damaged bales (246 g/kg of moisture; 23 mm of total rainfall); L, low-moisture bales (99 g/kg of moisture); L–R, low-moisture, rain-damaged bales (93 g/kg of moisture; 72 mm of total rainfall); I, ideal-moisture bales (164 g/kg of moisture); NDF, neutral-detergent fiber; NDIN, neutral-detergent insoluble N 夽 Contribution No. 01087 of the Arkansas Agricultural Experiment Station. ∗ Corresponding author. E-mail address: [email protected] (W.K. Coblentz). 0377-8401/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0377-8401(03)00209-8
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of tall fescue hay was relatively small, but damage increased substantially with multiple rainfall events. © 2003 Elsevier B.V. All rights reserved. Keywords: Tall fescue hay; Baling; Rainfall event
1. Introduction Tall fescue is the primary cool season grass forage in the eastern half of the United States (Sleper and Buckner, 1995). The primary area of its adaptation is the upper south, an area noted for high relative humidity and a high probability of rainfall events. The recommended growth stage for hay harvest is boot stage to early heading (Ball et al., 1996), which often coincides with a high probability of rainfall. For example, the expected monthly norms for rainfall in April, May, and June in Fayetteville (Arkansas, USA) are 110, 129, 134 mm, based on data compiled between 1971 and 2000 (National Oceanic and Atmospheric Administration, 2002). This can delay harvest, thereby decreasing nutritive value and subsequent animal performance. The alternative to delaying harvest is to subject fescue hay crops to a higher probability of rain damage. Effects of rainfall on nutritive value are well known for alfalfa (Medicago sativa L.), but limited information is available for most grasses. Rainfall events during forage wilting can reduce dry matter (DM) yields, and the possibility of losing the entire crop exists if rainfall persists for extended periods of time (Rotz and Abrams, 1988). Collins (1982) determined that nonstructural carbohydrates are a primary component of the DM leached from rain-damaged forage. This reduces the forage digestibility, while increasing concentrations of the fibrous components within the forage (Collins, 1982, 1983; Fonnesbeck et al., 1982; Rotz and Abrams, 1988). Some studies suggest that concentrations of N and minerals are minimally affected by rain damage (Collins, 1985), while other research indicates that concentrations of N may actually increase slightly after rainfall events (Rotz et al., 1991), because some N fractions are less soluble than other components of forage DM. High probabilities of rainfall may also persuade hay growers to package and store hay at concentrations of moisture that are greater than the 200 g/kg threshold level that is generally recommended for acceptable storage characteristics. Concentrations of moisture greater than 200 g/kg provide a favorable environment for growth of microorganisms in hays during storage. Typically, these microorganisms oxidize nonstructural carbohydrates preferentially for energy, and produce heat via respiration. Additional deleterious effects of spontaneous heating in forages include mold growth, increased concentrations of fiber, reduced digestibility, and nonenzymatic browning that can decrease bioavailability of N (Coblentz et al., 2000). Many investigations of rainfall effects on wilting forages have been conducted with legumes, but relatively little work has focused on the examination of these effects in grasses. Improved knowledge of effects of rainfall on wilting forages would be valuable to livestock and hay producers. The objective was to assess the influence of natural
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rainfall, baling moisture, and spontaneous heating on the nutritive value of tall fescue hay. 2. Materials and methods 2.1. Sample generation A well-established stand of endophyte-infested ‘Kentucky-31’ tall fescue was harvested when fully headed with a disc mower on 23 May 2000 at the University of Arkansas Forage Research Area in Fayetteville (36◦ 05 N; 94◦ 10 W; elevation 394.5 m). The mower did not include a conditioning device and forage used in this study was the initial spring growth. Fertilization consisted of 56 kg/ha N applied as ammonium nitrate on 25 February 2000. The initial harvest was mowed in three blocks of 10 swaths each and allowed to dry until 24 May, when the highest desired concentration of moisture was reached (Table 1). On this date, two swaths were raked together prior to baling at 08:30 h with a side-delivery rake. Raked double-rows in each block were randomly assigned to one of three moisture concentrations chosen to provide slightly higher than ideal (H), ideal (I), and lower (L) than ideal concentrations of moisture at baling (224, 164, and 99 g/kg, respectively). The H, I, and L treatments were all baled on 24 May. Ideal moisture was based on the 200 g/kg threshold for acceptable storage of conventional rectangular bales suggested by Collins et al. (1987). Paired swaths, selected randomly within each field block immediately after mowing, were purposely not raked. These swaths remained in the field after baling the three initial treatments (i.e., H, I, and L), thereby allowing the option of baling rain-damaged forage if weather conditions permitted. A 23 mm rainfall event occurred after baling was Table 1 Timeline for mowing, raking, and baling events as well as cumulative rainfall for each of the five tall fescue baling treatmentsa Date
Treatments mowed
23 May 24 May 25 May 26 May 27 May 28 May 29 May
H, I, L, H–R, L–R
a
Treatments baled
Raking time (h of day)
Precipitation (mm)
Cumulative precipitation prior to balingb (mm)
H, I, L
23d
0
H–R
08:30c 15:00e 08:00e
45f 4
23
L–R
11:00g
72
H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). b Total precipitation that fell prior to baling the treatments identified on that date. c Treatments H, I, and L were raked at 08:30 h. d Precipitation fell after baling of H, I, and L treatments was complete. e Treatments H–R and L–R were raked at these times. f Precipitation fell after baling of H–R treatment was complete. g Only treatment L–R was raked at this time.
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completed on 24 May. Rained-on swaths within each block were inverted at 15:00 h on 25 May to enhance drying. These swaths were raked together at 08:00 h on 26 May and baled at 10:00 h at a higher than ideal concentration of moisture (246 g/kg; H–R). A second 45 mm rainfall event began at 10:30 h the same day, which limited the H–R baling treatment to two replications. A third 4 mm rainfall event occurred the following day (27 May). On 28 May, swaths from the remaining forage were inverted and allowed to dry until 11:00 h the following day, when the final baling treatment was obtained at a low concentration of moisture (93 g/kg; L–R). The L–R treatment received a cumulative total of 72 mm of rainfall prior to baling. For each combination of moisture and field block, 12 conventional rectangular bales (average size = 0.48 m × 0.38 m × 0.93 m) were made with a New Holland Model 320 baler (Ford New Holland, Inc., New Holland, PA). The method of stacking the baling treatments was similar to that reported previously (Coblentz et al., 2000; Turner et al., 2002). Wooden pallets were placed on the floor of an open-air pole barn. Six bales from each group of 12 were placed side by side, strings up, on top of the wooden pallets. The remaining six bales from each replication were positioned in the same orientation on top of the first six bales, thereby creating stacks two bales high and six bales wide for each field replication of each treatment. Individual stacks containing 12 bales were surrounded on the sides and top by dry bales of wheat straw to limit effects of diurnal variations in ambient temperature. Stacks were created within approximately 2 h of baling. All bales were weighed and measured to determine bale density prior to storage. Core samples were taken from two bales within each replicate of 12 bales prior to stacking and at 4, 8, 12, 24 days post-baling using a Uni-Forage Sampler (Star Quality Samplers, Edmonton, AB, Canada) fitted to an electric drill. These sampling intervals were based on the original baling date and so sampling times did not occur on the same calendar date for each treatment. A final, post-storage, sampling date occurred on the same calendar date for all treatments, which was 45 days after baling for H, I, and L bales, 42 days after baling for H–R bales, and 40 days after baling for L–R bales. By the final sampling date, the internal bale temperatures of all bales had been ambient for at least 10 days. Bales were assigned randomly to one of the six sampling dates, and each pair of bales sampled on a given date contained one bale from both the top and bottom storage layers. Based on previous temperature vs. time in storage curves for other forages (Coblentz et al., 1996, 2000; Turner et al., 2002), these sampling dates were selected to approximately coincide with several key portions of a typical heating curve. These included: (i) the end of the initial heating period (day 4); (ii) the onset, peak, and end of the secondary heating phase (days 8, 12, and 24, respectively); and (iii) the end of the study (day 40 for L–R, day 42 for H–R, or day 45 for H, I, and L). The day 0 sampling date served as a pre-storage estimate of forage nutritive value. Eight core samples totaling between 60 and 120 g were taken from each bale (i.e., four cores per end). Bales were removed from each stack for sampling and then returned to their previous location in the stack for the remainder of the trial to maintain the integrity of the stack. All forage samples were dried under forced air at 55 ◦ C for 72 h. For bales sampled on day 0, this technique was used to estimate the initial concentration of moisture for each baling treatment. Recoveries of DM were determined from calculated DM weight of each bale before and after storage.
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Bales sampled after storage were visually appraised for mold growth by the method of Roberts et al. (1987) using a five point scale where: 1, no visible mold; 2, presence of spores between flakes; 3, presence of spores throughout the bale; 4, mycelial mat between flakes; and 5, mycelial mat throughout the bale. When appropriate, increments of 0.25 were used to evaluate each bale. 2.2. Temperature analysis Prior to stacking, bales assigned to the 24 days and post-storage sampling dates were fitted with single thermocouple wires inserted into the center of each bale. Bale temperatures were recorded twice daily at 06:30 and 15:00 h until all treatments had been in storage for 14 days and once daily at 15:00 h during the remainder of the storage period. Temperature data was collected with an Omega 450 AKT Type K thermocouple thermometer (Omega Engineering, Stamford, CT). The observed temperature was considered to be the mean internal bale temperature for a given day, except during the initial 14 days, when the mean of the two observations was used. For each day of storage, heating degree days >30 ◦ C (HDD) were calculated by subtracting 30 ◦ C from the mean internal bale temperature. These differences were then summed over the entire storage period. Therefore, HDD is a single number that represents both the magnitude and duration of heating in each bale. Other temperature-related response variables included maximum temperature, minimum temperature, and the average temperature over the entire storage period. 2.3. Chemical analysis of forage Dry forage samples were ground through a Wiley mill fitted with a 1 mm screen (Arthur H. Thomas, Philadelphia, PA) and subsequently analyzed for N, neutral-detergent fiber (NDF), acid-detergent fiber (ADF), lignin, neutral-detergent insoluble N (NDIN), and acid-detergent insoluble N (ADIN). The NDF, ADF, and lignin analyses were conducted using batch procedures outlined by ANKOM Technology Corp. (Fairport, NY). Sodium sulfite and heat-stable ␣-amylase were omitted from the NDF procedure. These methods have been described and subsequently compared to conventional methods by Vogel et al. (1999) and found to give comparable results. Similar agreement between conventionally filtered and filter-bag procedures also have been reported for NDF (Komarek, 1993) and ADF (Komarek et al., 1994). Both NDF and ADF are expressed with residual ash. Nitrogen was quantified by a modified Kjeldahl procedure (Kjeltech Auto 1030 Analyzer, Tecator, Inc. Herndon, VA); the N concentrations in NDF (NDIN) and ADF (ADIN) residues were determined by procedures identical to those used for total N, and reported on the basis of total DM and N. Procedures for determination of NDIN and ADIN were consistent with the guidelines established by Licitra et al. (1996) with the exception that the ANKOM filter-bag method was used for digestion of forages in neutral and acid detergent. 2.4. In situ analysis A ruminally cannulated crossbred steer weighing 481 kg was used to determine the disappearance of DM after a 48 h ruminal in situ incubation for bale samples obtained before
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and after storage. The University of Arkansas Institutional Animal Care and Use Committee approved surgical procedures and anesthesia for the cannulation and care of the steer. The single 48 h endpoint was utilized to determine relative rankings of in situ disappearance, not to estimate actual in vivo DM digestibility. In a review, Weiss (1994) noted that in most studies the in situ DM disappearance at 48 or 72 h was correlated to DM digestibility in vivo, and this experimental approach ranked forages fairly consistently with in vivo data. Only a single steer was needed because duplicate bags of all field replications easily could be incubated within the same animal. The steer was housed in an individual 3.4 m × 4.9 m pen with a concrete floor that was cleaned regularly, and it was offered an alfalfa hay-based diet at a maintenance energy level of intake (i.e., 1.15% of body weight) throughout the trial (Vanzant et al., 1998). The ration contained 90% alfalfa hay (30.4 g/kg N, 444 g/kg NDF) and 10% corn grain-based supplement (983 g/kg cracked corn, 0.17 g/kg liquid molasses, 13.4 g/kg trace mineral salt, 0.9 g/kg Vitamins A, D, E premix, 1.3 g/kg Vitamin E premix, and 1.1 g/kg Rumensin 80® (176 mg/g monensin; Elanco Animal Health, Indianapolis, IN)). The steer had ad libitum access to water throughout the trial. The diet was offered in equal portions at 06:30 and 16:30 h, and the steer was adapted to the basal diet for 10 days prior to initiating the trial. Dacron bags (10 cm × 20 cm; 53 ± 10 mm pore size; Ankom Technology Corp., Fairport, NY) were filled with 5 g of dried forage that had been ground through a 1 mm screen in a Wiley mill. Dacron bags were heat-sealed using an impulse sealer (Model CD-200; National Instrument Co. Inc., Baltimore, MD). Duplicate bags were placed in a 36 cm × 50 cm mesh bag. Four mesh bags each containing 28 dacron bags (total of 112) were placed in the ventral rumen prior to the 06:30 h feeding and incubated for 48 h. Following incubation, all dacron bags were subjected to 10 cold-water rinse cycles in a commercial, top-loading washing machine (Model LXR7144EQ1, Whirlpool Corp., Benton Harbor, MI). Rinse cycles consisted of a 1 min agitation and a 2 min spin per rinse cycle (Coblentz et al., 1997; Vanzant et al., 1998). Rinsed dacron bags were dried to a constant weight at 50 ◦ C and allowed to equilibrate with air before analysis for residual DM (Vanzant et al., 1996). In situ disappearance was calculated as the proportion of forage DM that disappeared from the dacron bags during the 48 h ruminal incubation. 2.5. Statistical analysis Moisture concentration, bale measurements, and their associated storage characteristics were analyzed as a randomized incomplete block design by PROC GLM of SAS (1990). Four treatments (H, I, L, and L–R) contained three field replications, while treatment H–R had two. Single degree-of-freedom contrasts were used to compare least-square means for both initial bale characteristics and storage characteristics. A similar approach was used to evaluate indices of nutritive value prior to storage (day 0) and after storage by independent analyses of variance. In this study, bales were sampled on six dates throughout the storage period, and indices of nutritive value were evaluated for each of these sampling dates. In addition to the analyses of nutritive value described for pre- and post-storage hays, changes over time in storage were evaluated using storage time as a continuous variable. Initially, our model included linear, quadratic, cubic, and quartic effects, but these terms frequently interacted (P < 0.05)
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with baling treatment. Therefore, the response over storage time for each baling treatment was evaluated independently using PROC REG of SAS (1990). When the highest order term for storage time (i.e., quartic, cubic, quadratic, or linear) was not significant (i.e., P > 0.05), it was removed from the model and the data was re-analyzed. This was repeated until the highest order term remaining in the model was significant (P < 0.05). Throughout all aspects of the study, statistical significance was declared at P < 0.05; while potential trends of importance to the discussion and explanation of the results were identified at the P < 0.10 level of confidence. 3. Results and discussion 3.1. Bale characteristics Bale characteristics were affected by the concentration of moisture in the forage at the time of baling (Table 2). Bale length was longer (P = 0.003) by 0.03–0.06 m for hays baled under the 200 g/kg moisture threshold for acceptable storage (Collins et al., 1987), than for hays baled at concentrations of moisture that exceeded this threshold. This was true for hays that did not receive rain prior to baling (P = 0.018) and for hays receiving rainfall prior to baling (P = 0.003). Despite these differences in bale length, bale volume was not affected. As expected, bale weight and density on both a wet and dry basis were greater for H and H–R bales compared to those baled at acceptable concentrations of moisture (P ≤ 0.0004). This also was true within the more limited context of hays receiving no rain damage (P ≤ 0.002), and for hays damaged by rain (P ≤ 0.003). Generally, bale densities observed in this study, which ranged from 114 to 211 kg/m3 on an as-is basis, were comparable to those reported for bermudagrass hays made at similar moisture concentrations with the same haying equipment (Coblentz et al., 2000). 3.2. Temperature responses Internal bale temperature vs. time curves for selected baling treatments are shown in Fig. 1. The responses of the H and H–R bales were similar to those exhibited by both alfalfa and bermudagrass packaged at moisture concentrations greater than 200 g/kg (Coblentz et al., 1997, 2000; Turner et al., 2002), while the I, L, and L–R bales exhibited minimal heating responses. The sharp decline in internal bale temperatures between 12 and 15 days of storage was the result of relatively low overnight ambient temperatures that approached 10 ◦ C. It is likely that these relatively low ambient temperatures inhibited spontaneous heating within these hays. For example, Rees (1982) has indicated that growth of microorganisms in hay is often restricted when internal bale temperatures fall below 20 ◦ C. The HDD accumulated during the storage period were greater (P < 0.0001) for H and H–R bales than for bales packaged at concentrations of moisture <200 g/kg (Table 2). Despite its higher concentration of moisture at baling, the H–R bales accumulated fewer (P = 0.028) HDD than H bales. This could have occurred because nonstructural carbohydrates were leached from the H–R hay, thereby reducing the pool of available sugars that could potentially support spontaneous heating. However, a simpler explanation may
54
Moisture content (g/kg) Treatmentc H I L H–R L–R S.E.d
225 164 99 246 93 5
Contrastse (P > F) 1 <0.0001 2 <0.0001 3 <0.0001 4 0.009
Bale length (m)
Bale volume (m3 )
0.90 0.91 0.94 0.91 0.96 0.01
0.167 0.167 0.173 0.170 0.177 0.004
34.8 26.6 22.6 31.2 20.1 1.5
211 160 131 186 114 10
0.003 0.018 0.003 0.311
0.194 0.374 0.171 0.550
<0.0001 0.0002 0.001 0.085
<0.0001 0.0001 0.001 0.057
Bale weight (as-is) (kg)
Bale density (as-is) (kg/m3 )
Bale weight (DM basis) (kg)
Bale density (DM basis) (kg/m3 )
27.0 22.3 20.4 25.4 18.4 1.2
164 134 118 151 104 7
0.0004 0.002 0.003 0.251
0.0002 0.001 0.001 0.170
HDD
MAX (◦ C)
163 32 14 129 5 10
49.8 40.0 42.8 50.8 31.4 1.3
<0.0001 <0.0001 <0.0001 0.028
<0.0001 0.0002 <0.0001 0.658
Visible moldb
DM recovery (g/kg)
31.2 27.7 24.8 29.8 24.8 0.3
1.75 1.08 1.00 1.71 1.04 0.28
934 965 981 959 947 23
<0.0001 <0.0001 <0.0001 0.006
0.017 0.032 0.114 0.847
AVG (◦ C)
0.413 0.122 0.597 0.350
HDD, heating degree days >30 ◦ C; MAX, maximum internal bale temperature; and 40-day AVG, average internal bale temperature over the entire 40-day storage period. Visible mold assessment score: 1, no visible mold; 2, presence of spores between flakes; 3, presence of spores throughout the bale; 4, mycelial mat between flakes; and 5, mycelial mat throughout the bale (Roberts et al., 1987). c H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). d Standard error of the mean for the H–R treatment with n = 2 replications. Other treatments had n = 3 replications. e 1: all high moisture (H, H–R) vs. all low moisture (I, L, L–R); 2: high moisture (H) vs. low moisture (I, L) without rain; 3: high moisture (H–R) vs. low moisture (L–R) with rain; and 4: high moisture without rain (H) vs. high moisture with rain (H–R). a
b
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Table 2 Bale characteristics of tall fescue hay made at five concentrations of moisture and with or without natural rainfalla
J.E. Turner et al. / Animal Feed Science and Technology 109 (2003) 47–63
55
55 50
Temperatue,˚C
45 40 35 30 25 20 15 0
5
10
15
20
25
Fig. 1. Internal bale temperature during the initial 25 days of bale storage for three baling treatments (S.E. = 1.9 ◦ C) of tall fescue hay: H (䊐, 225 g/kg moisture, no rain); I (䊏, 164 g/kg moisture, no rain); and H–R (䊉, 246 g/kg moisture, 23 mm rain).
be that the H–R treatment had a 2-day shorter interval of time in storage prior to the onset of relatively cooler weather. In a pattern similar to that observed for HDD, the average, minimum, and maximum internal bale temperatures were higher for H and H–R bales than for those packaged at <200 g/kg of moisture. The H bales exhibited a higher (P = 0.006) average internal bale temperature than did H–R bales, but this was not related to maximum temperature, which did not differ between the two treatments. Visible mold score (Table 2) was higher (P = 0.017) for H and H–R hays compared to the other drier hays (I, L, L–R). This difference was also observed within hays receiving no rain damage prior to baling and H bales had a higher (P = 0.032) visual mold score than I and L. However, for rain-damaged hays, H–R bales did not differ from the L–R or H bales. Generally, the low visible mold scores, which did not exceed 1.75 for any treatment, can be explained on the basis of the low overnight temperatures that occurred between 12 and 15 days of storage and the comparatively low concentrations of moisture in these bales at baling. The DM recovery did not include field losses associated with rainfall events, because DM recovery was determined from the DM weight of each bale immediately prior to storage and after the storage period of approximately 6 weeks. No contrasts differed. 3.3. Nutritive value prior to storage The concentrations of fiber components and the in situ 48 h DM disappearance for the five baling treatments sampled immediately after baling (day 0) are in Table 3. There was no difference between I and L for any of these response variables, providing little evidence of leaf shatter in the driest (L) forage, and any extra wilting time used by growers to attain excessively low-moisture levels serves little practical purpose with small rectangular bales. However, it remains unclear whether these observations are true for large round bale
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Table 3 Concentrations of fiber and nitrogen components and 48 h in situ DM disappearance for tall fescue hay sampled immediately after baling (day 0)a NDF (g/kg)
ADF (g/kg)
Baling treatmentc H 663 I 677 L 673 H–R 720 L–R 764 3 S.E.d
376 383 381 405 426 3
Contrastse 1 2 3 4
0.0001 <0.0001 0.001 0.476
(P > F) <0.0001 <0.0001 <0.0001 0.348
Lignin (g/kg)
DM N disappearanceb (g/kg) (g/kg)
NDIN ADIN NDIN ADIN (g/kg) (g/kg) (g/kg N) (g/kg N)
48.1 51.2 49.8 54.8 55.2 1.5
641 629 639 618 597 9
2.27 2.37 1.87 2.44 2.60 0.20
0.87 1.07 1.00 1.04 1.07 0.05
0.164 0.020 0.447 0.025
0.345 0.110 0.682 0.300
0.017 0.005 0.847 0.413
0.075 0.0001 0.088 0.297
12.6 13.1 12.7 13.5 13.7 0.5 0.232 0.088 0.784 0.476
179 180 147 182 192 12 0.369 0.081 0.554 0.047
70.7 82.5 79.9 76.6 78.4 4.6 0.835 0.880 0.774 0.628
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; N, nitrogen; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b DM disappearance measured by incubating forages for 48 h in situ. c H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). d Standard error of the mean for the H–R treatment with n = 2 replications. Other treatments had n = 3 replications. e 1: one rainfall event (H–R) vs. no rain (H, I, L); 2: multiple rainfall events (L–R) vs. no rain (H, I, L); 3: single rainfall event (H–R) vs. multiple rainfall events (L–R); and 4: ideal moisture (I) vs. excessively dry (L).
packages. Concentrations of NDF, ADF, and lignin increased as the forage was exposed to rainfall events. This was not an unexpected result since others (e.g., Collins, 1982, 1983, 1985; Rotz and Abrams, 1988; Rotz et al., 1991) have reported an increase in concentrations of fiber components in response to rain damage. Contrasts of H–R hay with hays receiving no rain damage (H, I, and L) were significant (P ≤ 0.017) for each of the response variables. Contrasts of forage receiving 72 mm of cumulative rainfall prior to baling (L–R) with hays receiving no rain damage also were highly significant (P ≤ 0.005) for these fiber components. For NDF and ADF, H–R and L–R hays differed (P ≤ 0.001), but this response was not observed for lignin (P = 0.847). Generally, L–R bales exhibited the greatest increases in NDF and ADF concentrations. Respective increases of these fiber components were 101 and 50 g/kg relative to those measured for H bales. For H–R bales, increases in NDF and ADF were approximately half (57 and 29 g/kg, respectively) those observed for L–R bales. Clearly, these responses reflect the differences in cumulative rainfall prior to baling for the H–R and L–R treatments. The higher concentrations of fiber in the H–R and L–R hays are likely an indirect result of leaching, and prolonged or reactivated respiration of nonstructural carbohydrates, not actual accumulation of additional fiber (Collins, 1982). Pre-storage in situ DM disappearance after a 48 h ruminal incubation (Table 3) was higher (P = 0.0001) for baling treatments that were not exposed to rainfall (629–641 g/kg) than
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for the L–R baling treatment (597 g/kg). In situ DM disappearance for the H–R baling treatment (618 g/kg) was intermediate between hays receiving no rain damage and L–R hay, and only tended (P = 0.075 and 0.088, respectively) to differ from each. Generally, a single 23 mm rainfall event depressed in situ DM disappearance by only 11–23 g/kg, which is likely to have little biological significance. Generally, contrasts evaluating N components in baling treatments prior to storage were not significant, indicating little effect of rainfall on these hays. Concentrations of NDIN (g/kg DM) for L–R bales were higher (P = 0.020) than observed in hays receiving no rain damage. There were tendencies (P ≤ 0.088) for total N and NDIN (g/kg N) to differ between L–R hay and treatments receiving no rain damage, but these tendencies were not observed when hays receiving no rain damage were compared with H–R hay. There were no differences between H–R and L–R hays for any N-related response variable. Concentrations of NDIN (g/kg N) differed (P = 0.047) between I and L treatments, indicating there was a response to excessive dessication, but the lower concentration of NDIN in L hay would not be consistent with increased leaf shatter and the reasons for this observation remain unclear. 3.4. Comparisons of hays after storage Comparisons of nutritive value for treatment hays sampled after a storage period of approximately 6 weeks (Table 4) are probably the most meaningful for livestock and hay producers. Concentrations of NDF and ADF in hays damaged by natural rainfall, spontaneous heating during storage, or both (H, H–R, and L–R) were greater (P < 0.0001) than observed for undamaged hays (I, L). Similarly, concentrations of NDF and ADF were higher (P ≤ 0.0002) in rain-damaged hays (H–R, L–R) than in hays receiving no rain prior to storage (H, I, L), and also were higher (P ≤ 0.001) in hays that heated spontaneously (H, H–R) vs. hays that incurred minimal or no heating during storage (I, L, L–R). The concentration of NDF in H–R bales was higher (P = 0.003) by 40 g/kg than in H bales that also heated, but received no rain damage. However, there were no differences (P = 0.195) in concentrations of ADF between H–R and H bales. After storage, concentrations of lignin were relatively consistent across treatments. There was a tendency (P = 0.058) for rain-damaged hays to have higher concentrations of lignin than hays receiving no rainfall prior to storage. However, all other contrasts were not significant. The I and L baling treatments had higher (P < 0.0001) post-storage in situ DM disappearance than the other baling treatments that incurred rain damage, spontaneous heating, or both. This can probably be explained on the basis of better conservation of nonstructural carbohydrates in the absence of rain damage and spontaneous heating. After the 40–45-day storage period, in situ DM disappearance of H, H–R, and L–R bales were virtually identical, and ranged from 31 to 35 g/kg less than the I and L treatments. After storage, hays that incurred spontaneous heating (H and H–R) had a tendency (P = 0.069) for higher concentrations of total N than hays with minimal spontaneous heating (Table 4). High-moisture hays that lose carbohydrates via respiration during storage are known to exhibit slight increases in total N in the short term (<60 days; Rotz and Muck, 1994). For damaged hays that incurred spontaneous heating, rain damage, or both, NDIN and ADIN concentrations were higher (P ≤ 0.001) than observed in undamaged hays. Elevated concentrations of NDIN and ADIN also were observed in comparisons of rain-damaged
58
NDF (g/kg)
ADF (g/kg)
Baling treatmentc H 745 I 705 L 681 H–R 785 L–R 760 7.1 S.E.d
434 411 397 444 440 5.1
Contrastse (P > F) 1 <0.0001 2 <0.0001 3 <0.0001 4 0.003
<0.0001 0.0002 0.001 0.195
a
Lignin (g/kg) 58.9 62.0 58.3 64.7 68.3 3.86 0.224 0.058 0.731 0.270
DM disappearanceb (g/kg) 598 629 632 596 597 7.5 <0.0001 0.001 0.001 0.866
N (g/kg)
14.3 13.1 12.7 13.7 12.3 0.7 0.372 0.592 0.069 0.575
NDIN (g/kg)
ADIN (g/kg)
3.63 2.47 1.93 3.59 2.43 0.16
1.47 0.83 0.93 2.10 1.57 0.12
<0.0001 0.028 <0.0001 0.838
<0.0001 <0.0001 0.0001 0.003
NDIN (g/kg N)
ADIN (g/kg N)
255 189 153 260 199 16
104.4 63.8 75.8 155.0 130.3 12.0
0.001 0.042 0.0004 0.826
0.0003 0.0004 0.005 0.015
NDF, neutral-detergent fiber; ADF, acid-detergent fiber; N, nitrogen; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. DM disappearance measured by incubating forages for 48 h in situ. c H, high-moisture bales (225 g/kg); I, ideal-moisture bales (164 g/kg); L, low-moisture bales (99 g/kg); H–R, high-moisture, rained-on bales (246 g/kg, 23 mm total rainfall); and L–R, low-moisture, rained-on bales (93 g/kg, 72 mm total rainfall). d Standard error of the mean for the H–R treatment with n = 2 replications. Other treatments had n = 3 replications. e 1, all damaged hays (H, H–R, L–R) vs. no damage (I, L); 2, rain-damaged (H–R, L–R) vs. no rain (H, I, L); 3, spontaneous heating (H, H–R) vs. minimal heating (I, L, L–R); and 4, spontaneous heating and rain (H–R) vs. heating only (H). b
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Table 4 Concentrations of fiber and nitrogen components and 48 h in situ DM disappearance for tall fescue hay sampled after a storage period of approximately 6 weeksa
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hays with hays receiving no rain prior to baling (P ≤ 0.042), and for comparisons of hays that heated spontaneously with those that did not (P ≤ 0.005). In addition, these relationships were observed when NDIN or ADIN was expressed as a proportion of total plant DM or N. Concentrations of NDIN in H–R bales did not differ (P ≥ 0.826) from those found in H bales, but ADIN was higher (P ≤ 0.015) in H–R bales than in H bales that heated without previous rain damage during wilting. 3.5. Changes in nutritive value during storage In this study, bales were sampled on six dates throughout the storage period so that indices of nutritive value could be evaluated as a function of time in storage. Initially, there were numerous interactions (P < 0.05) of baling treatment with linear, quadratic, cubic, or quartic terms for storage time. Because of these interactions, relationships between indices of nutritive value and storage time were established for each individual baling treatment. Generally, changes in nutritive value due to time in storage were most obvious in bales that heated spontaneously (H and H–R; Tables 5 and 6, respectively). For treatments that incurred minimal spontaneous heating (I, L, and L–R), responses over time generally were static. Any regressions that were significant (P < 0.05) for these baling treatments tended to have narrow ranges of response over the storage period. For this reason, only data for Table 5 Regressions of concentrations of total N, fiber components, and N components on storage time for tall fescue hay baled at 225 g/kg of moisture without rainfall (H) and stored for approximately 6 weeksa Sampling date (days)
N (g/kg)
0 4 8 12 24 45 S.E.b
12.5 13.8 13.5 13.0 13.9 14.3 0.4
Modelc P > Fd
Linear 0.036
NDF (g/kg) 663 695 716 720 734 745 5 Cubic <0.0001
Coefficients Quartic Cubic Quadratic Linear
– – – 0.0291
– 0.00388 −0.317 8.19
RMSEe R2
0.82 0.246
10.3 0.897
ADF (g/kg) 376 387 402 408 397 434 4 Cubic <0.0001
Lignin (g/kg) 48.1 51.1 60.1 54.3 57.9 58.9 2.1 Quadratic 0.004
NDIN (g/kg N) 179 190 272 281 255 255 12 Cubic 0.003
ADIN (g/kg N) 70.7 64.3 83.9 91.9 105.7 104.4 7.4 Quadratic 0.001
– 0.00452 −0.296 5.53
– – −0.0102 0.652
– 0.0103 −0.803 17.2
– – −0.0371 2.56
7.16 0.890
3.53 0.528
31.7 0.628
13.4 0.598
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b Standard error of the baling treatment × sampling date interaction mean. c Best fit quartic, cubic, quadratic, or linear regression model. d F-test for regression model. e Root mean square error for the regression.
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Table 6 Regressions of concentrations of total N, fiber components, and N components on storage time for tall fescue hay baled at 246 g/kg of moisture after a single rainfall event of 23 mm (H–R) and stored for approximately 6 weeksa Sampling date (days)
N (g/kg)
0 4 8 12 24 42
13.4 13.4 12.9 13.9 13.5 13.7 0.5
S.E.b
NDF (g/kg)
ADF (g/kg)
Lignin (g/kg)
NDIN (g/kg N)
ADIN (g/kg N)
719 734 761 758 770 787
404 404 431 427 437 445
54.6 58.1 63.6 61.6 56.3 64.7
184 268 292 271 247 261
75.7 89.2 118.5 138.4 136.9 161.6
6
5
2.5
14
9.1
Quartic 0.001
Cubic 0.0001
Modelc
nsd
P > Fe
–
Cubic 0.0001
Linear 0.001
ns –
Coefficients Quartic Cubic Quadratic Linear
– – – –
– 0.0034 −0.256 6.31
– – – 0.946
– – – –
−0.00154 0.132 −3.59 34.2
– 0.00469 −0.349 8.54
RMSEf R2
– –
8.3 0.915
10.3 0.673
– –
12.7 0.924
11.0 0.913
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b Standard error of the baling treatment × sampling date interaction mean. c Best fit quartic, cubic, quadratic, or linear regression model. d Highest order independent term had a nonsignificant (P > 0.05) coefficient for quartic, cubic, quadratic and linear regressions. e F-test for regression model. f Root mean square error for the regression.
bales packaged at the ideal concentration of moisture (I) are presented to illustrate changes in nutritive value for bales that did not heat spontaneously (Table 7). One exception to this generalization was the concentration of ADIN in L–R bales, which increased quadratically (P = 0.001; R2 = 0.603) on a DM basis from 1.07 to 1.67 g/kg between days 0 and 12 of storage before declining slightly to 1.57 g/kg by the final sampling date (data not shown). Similarly, ADIN (g/kg N) increased linearly (P = 0.002; R2 = 0.479) from 78.4 to 130.3 g/kg N during storage (data not shown). The quartic model for I bales (P = 0.002; R2 = 0.720; Table 7) describing the relationship between ADIN (g/kg N) and storage time is equally difficult to explain. Both NDIN and ADIN should increase in response to spontaneous heating as this process occurs via nonenzymatic browning or Maillard reactions, and because these fiber-associated N components are not affected by microbial respiration or volatilization of ammonia and other N compounds during storage (Rotz and Muck, 1994). However, it remains unclear why rain damage profoundly affected concentrations of ADIN after storage. Concentrations of water insoluble N components, such as ADIN, are known to increase in response to rain damage (Rotz and Muck, 1994). However, this was not observed for ADIN in our bales sampled on day 0 (P ≥ 0.110;
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Table 7 Regressions of concentrations of total N, fiber components, and N components on storage time for tall fescue hay baled at 164 g/kg of moisture without rainfall (I) and stored for approximately 6 weeksa Sampling date (days)
N (g/kg)
NDF (g/kg)
0 4 8 12 24 45
13.1 13.2 13.0 13.1 13.3 13.1
677 667 677 688 693 705
0.4
5
S.E.b
ADF (g/kg)
Lignin (g/kg)
NDIN (g/kg N)
ADIN (g/kg N)
383 391 387 384 388 411
51.2 51.0 53.9 51.3 57.8 62.0
180 166 196 177 174 189
82.5 100.4 67.8 68.6 101.9 63.8
4
2.1
12
7.4
Modelc
nsd
P > Fe
–
Linear 0.0003
Coefficients Quartic Cubic Quadratic Linear
– – – –
– – – 0.754
– – 0.0204 −0.399
– – – 0.258
– – – –
−0.00103 0.0752 −1.46 6.68
RMSEf R2
– –
10.5 0.574
6.76 0.681
3.28 0.616
– –
10.5 0.72
Quadratic 0.0002
Linear 0.0001
ns –
Quartic 0.002
a NDF, neutral-detergent fiber; ADF, acid-detergent fiber; NDIN, neutral-detergent insoluble N; ADIN, acid-detergent insoluble N. b Standard error of the baling treatment × sampling date interaction mean. c Best fit quartic, cubic, quadratic, or linear regression model. d Highest order independent term had a nonsignificant (P > 0.05) coefficient for quartic, cubic, quadratic and linear regressions. e F-test for regression model. f Root mean square error for the regression.
Table 5). It is also unclear why the concentration of ADIN in L–R bales increased from 78.4 to 130.3 g/kg N during a 40-day storage period where the maximum internal bale temperature reached 31.4 ◦ C and only 5 HDD were accumulated. In contrast, rain damage affected concentrations of NDIN prior to storage. Higher (P = 0.020; Table 3) concentrations of NDIN (g/kg DM) were observed on day 0 for L–R bales receiving multiple rainfall events than in hays receiving no rain prior to baling, and a similar tendency (P = 0.081) was observed when NDIN was expressed as a proportion of total N. The best fit models for H and H–R bales (Tables 5 and 6) generally were nonlinear, which agrees with past work (Turner et al., 2002) indicating that concentrations of fiber components, NDIN, and ADIN in bermudagrass increase rapidly with the onset of microbial respiration, but then stabilize after 2–3 weeks of storage. For H bales, concentrations of total N increased linearly (P = 0.036; R2 = 0.246; Table 5) during storage, but this relationship was not observed (P = 0.473) in H–R bales. For H bales, the relationship between total N and storage time was weaker than observed for NDF, ADF, lignin, and NDIN, and ADIN expressed as a proportion of total N (P ≤ 0.004; R2 ≥ 0.528). Cubic models were especially effective in explaining the relationship between both NDF and
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ADF and storage time (P < 0.0001; R2 ≥ 0.890). For H–R bales, there was no relationship (P > 0.339) between N or lignin and storage time. However, cubic models were especially effective (P = 0.0001; R2 ≥ 0.913) at explaining this relationship for NDF and ADIN (g/kg N), while quartic models provided the best fit (P = 0.001; R2 = 0.924) for NDIN (g/kg N).
4. Conclusions Before storage, tall fescue hay exposed to rainfall had higher concentrations of NDF and ADF than hay not exposed to rainfall. Generally, total N and N components only were affected marginally in hay that was exposed to rainfall. Immediately after baling, in situ DM disappearance was reduced by 32–44 g/kg in hay that was exposed to 72 mm of rainfall, relative to hays that were not damaged by rain. Intermediate reductions in ruminal DM disappearance were observed for hay receiving 23 mm of rainfall prior to baling. Generally, changes in nutritive value in response to spontaneous heating were small because no hay was baled at >250 g/kg of moisture, but the maximum changes in nutritive value occurred in hays that exhibited measurable spontaneous heating. Ball et al. (1996) has described the drastic increases in NDF and concurrent decreases in digestibility that occur when tall fescue matures past late-boot stage. By comparison, the effects of a single 23 mm rainfall event appear to be relatively minor. However, some caution is advised in interpretation of these results. The two rain-damaged baling treatments received rain in different amounts and frequencies, were baled at different moisture levels, and remained in the windrow different intervals of time prior to baling. Therefore, factors other than the actual amount of rainfall received during wilting may have influenced the results, particularly in samples obtained immediately after baling before any spontaneous heating may have occurred. Generally, our findings suggest that producers could benefit from pursuing harvest more aggressively, even when there is some chance of rain before the crop is dry. However, these studies do not consider potential effects on palatability and subsequent intake by cattle.
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