Effects of the frequency of forage allocation and harvest maturity of whole-crop oat forage on dry matter intake and ruminal fermentation for beef heifers

The Professional Animal Scientist 33:85–91 https://doi.org/10.15232/pas.2016-01556 ©2017 American Registry of Professional Animal Scientists. All rights reserved.

Effects of the frequency of forage allocation and harvest maturity of whole-crop oat forage on dry matter intake and ruminal fermentation for beef heifers C. L. Rosser,* A. D. Beattie,† H. C. Block,‡ J. J. McKinnon,* H. A. Lardner,*§ P. Górka,# and G. B. Penner*1 *Department of Animal and Poultry Science, and †Department of Plant Sciences, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5A8; ‡Agriculture and Agri-Food Canada, Lacombe, AB, Canada, T4L 1W1; §Western Beef Development Centre, Humbolt, SK, Canada, S0K 2A0; and #Department of Animal Nutrition and Dietetics, University of Agriculture in Krakow, al. Mickiewicza 24/28, 30-059 Krakow, Poland

ABSTRACT

INTRODUCTION

The objective of this experiment was to determine whether feeding frequency of whole-crop oat forage harvested at 2 maturities affects forage intake and ruminal fermentation. Whole-crop oat forage (c.v. Weaver, Crop Development Centre, Saskatoon, SK, Canada) harvested at the hard dough and ripe stages were offered ad libitum either daily (1-D) or once every 3 d (3-D) to 4 ruminally cannulated heifers. Treatments were arranged in a 2 × 2 factorial within a 4 × 4 Latin square design. Because of low forage availability, one period was omitted, resulting in an incomplete Latin square. Diets were supplemented to ensure CP was balanced across treatments. Data were analyzed using the mixed model of SAS. Total DMI and forage intake were not affected by harvest maturity, feeding frequency, or the interaction (P ≥ 0.41). Minimum ruminal pH averaged over 3 d was less for heifers fed 3-D (5.53) compared with 1-D (5.89; P < 0.001). Mean pH increased from 5.81 to 5.99 and then 6.35 for d 1, 2, and 3, respectively, for heifers fed 3-D (frequency × day; P = 0.002). However, mean ruminal pH did not differ among days for heifers fed 1-D (average of 6.32). There was a frequency × day interaction for the total ruminal short-chain fatty acid concentration (P = 0.046), with the concentration being less for heifers on d 3 relative to d 1 when fed 3-D; however, no differences among days were detected for heifers fed daily. These data suggest that feeding 3-D may not affect forage intake but increases the risk for low ruminal pH, and transiently reduces ruminal short chain fatty acid concentrations.

Beef producers can reduce the costs associated with winter feeding by approximately 50% with adoption of extensive winter feeding strategies, such as swath grazing, instead of using dry-lot feeding systems (Volesky et al., 2002; McCartney et al., 2004). The reduction in winter feeding costs has been associated with reduced cost for feeding (Volesky et al., 2002), labor, and manure removal (McCartney et al., 2004). Although the recommendations for swath grazing are to allocate access to new forage on a frequent basis (Saskatchewan Ministry of Agriculture, 2009), producers may further reduce labor and operational costs by allocating a greater quantity of forage at each feeding event, thereby reducing the frequency of forage allocation. Whereas increasing the amount of forage allocated in a single feeding event may reduce costs, it may also enable cows to selectively consume specific plant parts on individual days (Kumar et al., 2012). Selective consumption could cause variability in the nutrient composition of the diet, fermentability of the consumed diet, and variation in DMI across days. For example, selective consumption of the cereal grain and leaves would result in a diet that is more digestible when compared with stems (Kilcher and Troelsen, 1973; Chow et al., 2008) and could result in a reduction in ruminal pH. Selective consumption of palatable components early in the grazing period would leave high-fiber components remaining for the later portion of the grazing period, which may be refused or reduce intake. It is currently recommended that whole-crop oat forage be harvested at the late milk stage (Kaulbars and King, 2004); however, there has been a suggestion that harvesting at a more advanced stage of maturity can increase nutrient yield without negatively affecting in situ digestibility (Rosser et al., 2013). Furthermore, a recent experiment has demonstrated that delaying the harvest of whole-crop oat forage from late milk to the mature stage increases yield and DMI, without a reduction in total-tract DM digestibility, or negative effects on ruminal fermenta-

Key words: feeding frequency, forage, harvest maturity, oat, swath grazing

Corresponding author: [email protected]

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Table 1. Environmental conditions1 and harvest dates of whole-crop oat (Avena sativa CDC Weaver) forage at the hard dough (HD) and ripe (RP) stages Temperature, °C Maturity Swathing3  HD  RP Baling4  HD  RP

  Date

Minimum Mean Maximum

  Aug 13, 2012 Aug 28, 2012   Aug 18, 2012 Sep 3, 2012

  −2.0 −2.0   4.9 6.4

  16.4 16.5   14.7 16.6

  32.2 32.2   24.6 31.0

Precipitation, Growing mm degree days2   273.3 298.3   4.3 0.8

  1,008.9 1,190.3      

Data derived from the Environment Canada Weather Monitoring Service (Diefenbaker International Airport, Saskatoon, SK, Canada; http://climate.weather.gc.ca/historical_data/ search_historic_data_e.html). 2 Calculated as (maximum temperature + minimum temperature) ÷ 2 − base, where the base is 5°C. 3 Data were calculated from seeding (May 17, 2012) until the swathing date. 4 Data were calculated from swathing to baling date, which was day forage was baled and moved into storage. 1

tion (Rosser et al., 2016). However, cattle in that experiment were fed daily. It is not clear whether the increase in starch content and more mature stems that occurs with whole-crop oat harvested at a greater maturity (Rosser et al., 2013) will affect DMI and variability in ruminal fermentation when forage is offered in larger quantities and allocated less frequently. Therefore, the objective of this experiment was to determine whether the feeding frequency and harvest maturity of whole-crop oat forage affects voluntary intake over a 3-d period and ruminal fermentation characteristics both daily and over a 3-d period.

MATERIALS AND METHODS Agronomic Practices On May 17, 2012, CDC Weaver oat (Avena sativa) was seeded into barley stubble at the University of Saskatchewan using a John Deere 9450 hoe drill (Deere and Co., Moline, IL) at a rate of 269 plants/m2 with a 25.4-cm row spacing. Weeds were controlled using Refine SG with MCPA Ester 600 (29.6 g/ha and 1.0 L/ha; E.I. DuPont Canada, Mississauga, ON, CA) applied on June 22, 2012. No fertilizer was applied. The forage was harvested at the hard dough (HD) and ripe (RP) stages as described by Rosser et al. (2013). The specific stage of maturity was defined when 50% of the field was at the appropriate stage. Whole-crop oat was cut using a Massey Ferguson 200 self-propelled swather (AGCO, Duluth, GA) leaving a 10-cm stubble height. The forage was allowed to cure in windrows until reaching a DM content >87% before baling using a Massey Ferguson

1835 square baler (AGCO). The bales were immediately stored in a covered shelter after baling. Environmental conditions during the growing and harvest periods were collected from the Environment Canada Weather Monitoring Service weather station at the Diefenbaker International Airport in Saskatoon, SK. The environmental conditions, harvest dates, and baling dates are shown in Table 1.

Heifers and Experimental Design All experimental procedures involving ruminally cannulated heifers were preapproved by the University of Saskatchewan Animal Research Ethics Board (Protocol No. 20100021) and followed the guidelines of the Canadian Council of Animal Care (2009). Four ruminally cannulated yearling heifers (initial BW ± SD of 441 ± 16 kg) were used in this experiment. Heifers were housed in individual pens (9 m2) with rubber mats on the floor. Heifers were exposed to 16 h of light and 8 h of darkness. Each pen was fit with a large wooden (1.2 × 1.2 × 1.2 m) feeder to enable 3 d of forage allocation while minimizing waste. The feeder contained an opening with an offset baffle to prevent cattle from removing and throwing forage. The experimental design consisted of a 4 × 4 Latin square with a 2 × 2 factorial treatment arrangement. Periods were 15 d including 9 d of adaptation and 6 d for data and sample collection. The main treatment factors evaluated were the maturity of whole-crop oat at the time of harvest (HD vs. RP) and the frequency of forage allocation [once daily (1-D) vs. once every 3 d (3-D)]. The whole-crop oat forage was allocated for ad libitum intake, targeting approximately 20% refusal of forage of-

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fered, regardless of the frequency of feeding. A target of 20% of refusals was used to enable measurement of voluntary DMI and allowed heifers to sort their feed as would occur under field-grazing settings. The whole-crop oat forage was fed at 0900 h daily for 1-D, and at 0900 h on d 1, 4, 7, 10, and 13 for 3-D. All heifers were also provided a supplement, at 0900 h daily, at a fixed rate of 0.6% of BW daily in a separate feeder to enable determination of supplement and forage intake. The supplement consisted of (DM basis) rolled barley and canola meal in combination (55%), alfalfa pellet (25%), and a vitamin and mineral supplement pellet with barley as a carrier (25%; Table 2). The supplement was designed to provide a means to offer additional forage (alfalfa pellet) and was similar to that described by Rosser et al. (2016). The proportion of rolled barley and canola meal were formulated in attempt to make diets isonitrogenous and isoenergetic.

Data and Sample Collection Heifers were weighed on 2 consecutive days before 0800 h at the start of each period. On each day of feed provision, the amount of feed allocated was weighed, and voluntary DMI was determined during d 10 to 15. Refusals were weighed before the morning feeding (daily for 1-D and on d 13 and d 1 of the next period for 3-D) and a sample equating to 10% of the refusal weight was collected at each sampling day and stored at −20°C for later analysis. Dry matter intake was calculated by subtracting the weight of the refusal from the weight of feed offered after feed and refusals were corrected for DM content. Feed samples were collected daily throughout d 10 to 15 and were composited by period. On d 10, 11, and 12, ruminal pH was measured every 5 min using an indwelling pH system described by Penner et al. (2006). The pH systems were standardized using pH buffers of 4 and 7 at 39°C. Standardization occurred before being inserted into the rumen on d 10 and the morning of d 13 of each period after removal from the rumen. Minimum, mean, and maximum ruminal pH was then calculated to obtain daily values as a 3-d measurement average. Ruminal digesta was collected from the cranial central, central, and caudal central regions (250 mL each) at 1400 and 2000 h on d 13; at 0200, 0800, 1400, and 2000 h on d 14; at 0200, 0800, 1400, and 2000 h on d 15; and 0200 and 0800 h on d 1 of the next period, but before feeding the subsequent treatment. Digesta from each region was combined and strained through 2 layers of cheesecloth. For short chain fatty acid (SCFA) and ruminal ammonia analysis, 10 mL of strained ruminal fluid was added to 2 mL of 25% (wt/vol) metaphosphoric acid and 2 mL of 1% sulfuric acid, respectively. For osmolarity analysis, 10 mL of the rumen fluid was collected at each sampling point. The rumen fluid samples were then stored at −20°C until further analysis.

Table 2. Ingredient composition of the supplement and nutrient content of the complete diet composed of whole crop oat (Avena sativa CDC Weaver) harvested at the hard dough (HD) and ripe (RP) stages Stage of maturity Item

HD

RP

Supplement composition, % DM   Alfalfa pellet   Vitamin and mineral supplement1   Rolled barley   Canola meal Nutrient concentration, % DM   DM, %  OM  CP  NDF  ADF  Starch   Crude fat  Ca  P

  25.0 20.0 34.0 21.0   93.5 90.9 14.5 44.1 27.7 22.1 2.6 0.9 0.5

  25.0 20.0 30.0 25.0   93.5 89.9 15.1 45.4 30.8 19.1 2.5 0.9 0.5

Major components (>5% of supplement) include ground barley (50.3%), corn dry distillers grains with solubles (25.0%), limestone (8.7%), Dynamate (6.8%; The Mosaic Company, Plymouth, MN), and canola meal (6.0%). Supplied 3.4% Ca, 0.5% P, 4.6 mg/kg Co, 146 mg/kg Cu, 335 mg/kg Mn, 2.3 mg/kg Se, 314 mg/kg Zn, 40,000 IU/ kg vitamin A, 15,000 IU/kg vitamin D, 300 IU/kg vitamin E, and 308 mg/kg of monensin (Elanco Division of Eli Lilly Canada Inc., Guelph, ON, Canada).

1

Chemical Analysis Feed and refusal samples were dried in a forced air oven at 55°C for 48 h to determine DMI. Feed samples were then ground using a hammer mill (Christy and Norris Ltd., Chelmsford, UK) to pass through a 1-mm screen. Feed samples were analyzed for DM, ash, CP, starch, ether extract, NDF including the use of sodium sulphite and α-amylase, ADF, Ca, and P at Cumberland Valley Analytical Services (Hagerstown, MD) as described by Rosser et al. (2013). Ruminal fluid samples collected from each cow were pooled on an equal volume basis within each period to obtain a single sample per cow per period. Subsequently, ruminal SCFA were analyzed by gas chromatography (Agilent 6890, Mississauga, ON, Canada) according to Khorasani et al. (1996). Ruminal ammonia was measured using a phenol hypochlorite assay (Fawcett and Scott, 1960). Ruminal osmolality was determined using a Model 3250 osmometer (Advanced Instruments Inc., Norwood, MA) after centrifugation (12,000 × g, 4°C, 10 min) of the ruminal fluid.

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Statistical Analysis Because of a shortage in forage, only the first 3 periods were completed, resulting in an incomplete Latin square. Data were analyzed using the Mixed Model procedure of SAS (Version 9.3, SAS Institute Inc., Cary, NC). For analysis of intake data, the fixed effects were period, wholecrop oat maturity, allocation frequency, and the interaction between maturity and frequency of allocation. Heifer was considered to be a random effect. To analyze ruminal fermentation characteristics, the fixed effects included in the model were period, wholecrop oat maturity, frequency of forage allocation, day, and the 2-way and 3-way interactions. Heifer was considered a random effect, and day within period was analyzed as a repeated measure. When significant interactions were detected (P < 0.05), means were separated using the Bonferroni post hoc mean separation test. Significance was declared when P ≤ 0.05. There were no significant 3-way interactions (data not reported).

RESULTS AND DISCUSSION Although not statistically analyzed the DM yields for HD and RP were 4.70 and 4.15 t/ha. The DM (at the time of cutting), OM, CP, NDF, and starch concentrations were 35.4, 91.1, 8.2, 61.0, and 14.5 for HD and 54.2, 89.9, 8.8, 60.9, and 12.8 for RP, respectively.

Total DMI, forage DMI, and supplement DMI over the 3-d feeding cycle were not affected by maturity, allocation, or the interaction between maturity and allocation (P ≥ 0.41), averaging 34.5, 26.2, and 8.3 kg/3 d, respectively (Table 3). To our knowledge there have not been any published experiments that have evaluated the effect of feeding whole-crop forages with various allocation durations (i.e., daily vs. 3 d); however, Ruiz and Mowat (1987) suggested that when feed was provided ad libitum, feeding frequency did not have an effect on DMI. Increasing the forage allocation can potentially result in high quality components of the forage being consumed the first day, leaving lower quality components for subsequent days. This could result in reduced DMI on the subsequent days, variation in nutrient availability and supply among days, and reduced utilization of the forage. Smith et al. (1974) found that when the feeding frequency was increased from daily to once every 4 d there was an increase in forage refusals as percentage of the amount offered. Although we did not evaluate selective consumption in the present experiment, the lack of effect for DMI and forage DMI suggests that forage feeding frequency and maturity of the forage do not affect voluntary consumption of forage. There were no interactions between oat maturity and frequency of forage allocation for ruminal pH (Table 3) except there was a tendency for area that pH was <5.8 (P = 0.060). Mean and minimum ruminal pH were less in heif-

Table 3. Dry matter intake and ruminal fermentation for heifers fed whole-crop oat (Avena sativa CDC Weaver) harvested at the hard dough (HD) and ripe (RP) stages when forage was provided daily (1-D) or as a 3-d (3-D) allocation HD Item DMI over 3 d, kg  Total  Forage  Supplement Ruminal pH  Maximum  Mean  Minimum   Duration pH <5.8, min/d   Area pH <5.8, pH × min/d Ruminal SCFA,1 mM  Total  Acetate  Propionate  Isobutyrate  Butyrate  Isovalerate  Valerate Ruminal ammonia, mg/dL Osmolality, mOsmol/kg 1

SCFA = short chain fatty acids.

RP

P-value

1-D

3-D

 

1-D

3-D

SEM

Maturity

Frequency

Maturity × frequency

  33.5 25.1 8.4   6.77 6.36 5.93 1.1 0.1   123.25 90.51 20.38 0.71 11.68 1.32 0.75 7.1 286.2

  36.1 27.9 8.2   6.69 6.10 5.64 273.3 44.7   129.36 81.33 33.11 0.86 11.72 2.23 1.03 8.1 284.5

                                       

  34.3 26.0 8.3   6.76 6.30 5.84 77.2 6.1   120.81 84.43 22.15 0.83 12.26 1.33 0.86 6.1 305.5

  34.2 25.8 8.4   6.74 5.99 5.43 502.8 158.5   131.34 78.50 36.81 0.87 11.58 2.12 1.11 6.4 322.4

  2.36 2.14 0.28   0.064 0.082 0.079 87.36 24.65   5.269 3.697 3.836 0.149 3.061 0.427 0.113 0.37 16.34

  0.79 0.74 0.86   0.72 0.32 0.088 0.119 0.041   0.95 0.28 0.43 0.64 0.93 0.81 0.22 0.040 0.11

  0.54 0.47 0.87   0.37 0.010 0.002 0.004 0.004   0.14 0.20 0.066 0.65 0.94 0.007 0.016 0.20 0.65

  0.52 0.41 0.64   0.78 0.75 0.44 0.41 0.060   0.62 0.68 0.82 0.78 0.93 0.83 0.84 0.52 0.58

Frequency of feeding and harvest maturity of whole-crop oat forage

ers when forage was allocated for 3-D instead of 1-D (P ≤ 0.010; Table 3). The duration and area that pH was <5.8 was also greater for 3-D compared with 1-D (P = 0.004). Lower ruminal pH for 3-D heifers is interpreted to suggest that heifers were effectively sorting for more fermentable components such as the grain and leaves of the oat forage to a greater extent than when fed 1-D. Research has demonstrated that heifers select for starch when fed wholecrop oat or barley harvested at the HD and RP stages (Rosser et al., 2016), and providing a greater quantity on a single day may enhance the ability of cattle to selectively consume highly fermentable plant parts. In addition to the feeding frequency, feeding whole-crop oat at RP relative to HD tended to reduce minimum ruminal pH (P = 0.088). Whole-crop oat forage that was harvested at RP had a larger area pH below 5.8 (P = 0.041) compared with HD. The reduction in pH for heifers fed RP compared with HD whole-crop oat suggests that cattle were selecting fermentable plant parts. That said, it is not clear why maturity may have influenced sorting and consequently ruminal pH. Although the digestibility of unprocessed oat is less than rolled oat (76.7 vs. 81.0) when fed as a cereal grain source (Toland, 1976), the reduction in pH in the current experiment with advancing maturity and the results of previous experiments (Rosser et al., 2013, 2016) suggest that starch in whole-crop oat is available for ruminal fermentation. In fact, Rosser et al. (2016) reported ruminal starch digestibility equal to or greater than 90% when oat was harvested at the late milk, hard dough, and ripe stages. There was no interaction between maturity and frequency of forage allocation for ruminal SCFA, ammonia, and osmolality (Table 3). Total ruminal SCFA concentration was not affected by harvest maturity or frequency of forage allocation, averaging 126 mM (P ≥ 0.14). Propionate concentration tended to be greater (P = 0.066) and isovalerate and valerate concentrations were greater (P ≤ 0.016) for 3-D compared with 1-D. Ruminal ammonia concentration was greater for HD compared with RP (averaging 7.6 and 6.3 mg/dL, respectively; P = 0.040). A previous experiment (Slyter et al., 1979) has indicated that ruminal ammonia concentrations greater than 4.5 mg/dL should be adequate for microbial protein synthesis and optimal nitrogen retention, suggesting that rumen degradable protein intake was adequate in the present diets. The effects of forage allocation and harvest maturity on ruminal fermentation characteristics throughout the 3-d feeding period are shown in Table 4. There were no 3-way interactions and no interactions between maturity of the forage at the time of harvest and day of the feeding cycle for any ruminal fermentation characteristics measured. However, heifers allocated forage for a 3-D duration had maximal pH values that were greatest on d 1 and 3 relative to d 2, whereas maximal pH did not differ among days for heifers allocated forage daily (1-D) and was intermediate to values measured for the 3-D heifers (allocation × day; P = 0.010). Mean ruminal pH was not different

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between days for 1-D heifers and was intermediate (average 6.33) relative to values observed for 3-D heifers. Mean ruminal pH of heifers allocated 3-D increased from d 1 to 3 (P = 0.001). Minimum ruminal pH was greater on d 1 for 1-D heifers than 3-D heifers, with no differences thereafter (frequency × day; P = 0.014). The duration and area that ruminal pH was below 5.8 was greatest for 3-D compared with 1-D, and for 3-D heifers the duration and area decreased with advancing days in the feeding cycle (P = 0.003). The change in the ruminal pH profile across days with the 3-D heifers, but not with the 1-D heifers, further supports the suggestion that providing an allocation of whole-crop forage for 3-D increases the ability of cattle to select fermentable plant parts early in the feeding period followed by cattle consuming less desirable and less fermentable plant parts toward the end of the forage allocation period. While using a more acute model, DeVries et al. (2005) formulated a diet to have a forage:concentrate ratio of 49:51 that was offered either once a day or twice a day. After feeding, they measured the forage-to-concentrate ratio of the refusals. They found that when the TMR was provided daily, the forage-to-concentrate ratio was 63:37, instead of 55:45 for the refusals from the cows fed twice daily. The results of DeVries et al. (2005) support the notion that providing a greater forage allocation may enable cattle to sort to a greater extent. Again, although not measured in the present experiment, reducing the frequency of forage allocation may also result in greater wastage of forage under field grazing settings. It is also important to note that the duration that pH was <5.8 was over 730 min on d 1 and over 360 min on d 2 of the 3-d forage feeding cycle for 3-D heifers. Research has suggested that pH values below 6.0 may decrease fiber digestibility (Calsamiglia et al., 2002). Ruminal pH values that limit fiber digestibility would represent a challenge for heifers fed high-forage diets. Although we did not measure ruminal or total-tract digestibility, a past experiment has demonstrated that ruminal NDF digestibility decreased as oat maturity increased from late milk, hard dough, and ripe stages (Rosser et al., 2016). The potential reduction in fiber digestibility may be an important consideration for producers feeding whole-crop forages with infrequent forage allocation. However, based on work by Rosser et al. (2016), it is not clear whether the reduction in fiber digestibility was due to lower ruminal pH or increased lignification of fiber with advancing maturity. Nevertheless, the data from the present experiment indicate that providing a greater forage allocation can result in low ruminal pH, even when fed a high forage diet. There was no 3-way interaction for ruminal SCFA or ammonia concentrations (data not shown; Table 4). Total ruminal SCFA concentrations were intermediate for 1-D, and 3-D on d 2 (average 125 mM), greatest for 3-D on d 1 (138 mM), and least for 3-D on d 3 (117 mM; allocation × day interaction, P = 0.046). This is likely due to the heifers preferentially sorting for grain, which is high in energy (Kilcher and Troelsen, 1973) as described above or that

  6.77ab 6.34ab 5.96a 5.0c 0.0b

Ruminal pH  Maximum  Mean  Minimum   Duration <5.8, min/d   Area <5.8, pH × min/d Ruminal SCFA,1 mM  Total  Acetate  Propionate  Isobutyrate  Butyrate  Isovalerate  Valerate Ruminal ammonia, mg/dL Osmolality, mOsmol/kg

  6.81a 5.81c 5.29c 736.7a 214.4a   138.37a 83.65 37.61 0.83 12.92 1.23 1.14 6.55 285.0

3-D                                

    6.77ab 6.31ab 5.84ab 79.2c 7.0b   123.18ab 88.47 21.47 0.75 11.95 1.31 0.80 6.61 287.7

1-D

3-D   6.51b 5.99bc 5.45bc 361.7b 79.5b   135.43ab 80.84 38.13 0.88 12.28 2.35 1.21 6.55 340.0

Day 2

Means with different superscripts within a row are different (P > 0.05). SCFA = short chain fatty acids.

a–c

1

122.14ab 87.02 21.09 0.84 12.51 1.43 0.83 6.60 318.1

1-D

Item

Day 1

                               

    6.76ab 6.33ab 5.86ab 33.3c 2.2b   120.76ab 86.92 21.25 0.70 11.46 1.23 0.78 6.59 281.6

1-D

3-D   6.81a 6.35a 5.86ab 65.8c 10.9b   117.26b 75.26 29.15 0.88 9.76 1.68 0.86 8.74 285.4

Day 3

  0.060 0.071 0.091 83.68 26.06   3.925 3.187 3.695 0.094 2.675 0.468 0.136 0.526 32.69

SEM

  0.012 0.001 0.049 0.007 0.004   0.027 0.23 0.16 0.45 0.43 0.14 0.13 0.13 0.66

Day

  0.010 0.001 0.014 0.003 0.003   0.046 0.28 0.19 0.087 0.67 0.38 0.20 0.12 0.41

Frequency × day

P-value

  0.29 0.79 0.91 0.82 0.13   0.94 0.92 0.99 0.86 0.76 0.95 0.99 0.93 0.72

Maturity × day

Table 4. Daily ruminal fermentation characteristics of heifers fed whole-crop oat (Avena sativa CDC Weaver) forage in either daily (1-D) or 3-d (3-D) allocations

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DMI varied among days. However, only the molar proportion of isobutyrate tended to be affected by the frequency × day interaction (P = 0.087). Ruminal ammonia and osmolality were not affected by forage feeding frequency; day; or the interactions between feeding frequency, maturity, and day (P ≥ 0.12).

Fawcett, J. K., and J. E. Scott. 1960. A rapid and precise method for the determination of urea. J. Clin. Pathol. 13:156–159.

IMPLICATIONS

Kilcher, M. R., and J. E. Troelsen. 1973. Contribution and nutritive value of the major plant components of oats through progressive stages of development. Can. J. Plant Sci. 53:251–256.

Providing forage in 3-d allocations did not negatively affect DMI over a 3-d duration but did cause marked changes in ruminal pH, with the lowest pH values generally occurring on d 1, intermediate values on d 2, and greatest pH values on d 3. The rumen fermentation data suggest that on the final day of the feeding period, the heifers were left with lower quality forage, which may have reduced their intakes. The variability in pH across days, especially for duration and area that pH was <5.5, were greater when the forage was harvested at RP than HD stages. Thus, feeding frequency of forage influences ruminal fermentation, and when feeding whole-crop forages, frequent feeding events are recommended to minimize risk for low ruminal pH.

ACKNOWLEDGMENTS Funding for this project was provided by the Saskatchewan Ministry of Agriculture’s Agriculture Development Fund. The authors would also like to acknowledge G. Gratton and R. Kanafas for their assistance with animal care, sample collection, and sample analysis.

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