Milk Production in High Producing Dairy Cows as Influenced by Corn Silage Quality

The Professional Animal Scientist 20 (2004):302–311

MilkDairyProduction in High Producing Cows as Influenced by Corn Silage Quality D. J. R. CHERNEY*,1, J. H. CHERNEY†, L. E. CHASE*, PAS, and W. J. COX† *Department of Animal Science and †Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853

Abstract Greater milk production is the promised outcome for selecting corn hybrids with various traits that impact forage quality. Our objective was to select a set of hybrids most likely to exhibit differences in forage quality and evaluate milk production of cows fed a high forage diet. Four hybrids were selected for the feeding trial: a leafy hybrid (Mycogen TMF 100威; Mycogen Seeds, Indianapolis, IN), a brown midrib (BMR) hybrid (Mycogen BMR F407威), and two conventional hybrids varying in fiber digestibility (Pioneer 36B08威 [Conventional 1 {CONV1}] and Pioneer 35P12威 [Conventional 2 {CONV2}]; Pioneer Hybrid International, Inc., Des Moines, IA). Diets were formulated to provide 1.0% BW as forage NDF (approximately 32% NDF) and were balanced to meet or exceed NRC requirements. Fifty-six cows were fed for 56 d. The DMI of cows fed the BMR and the leafy hybrid total mixed rations (TMR) were greater than those of cows fed the other hybrids. Differences in milk production reflected the differences in intake. Cows fed the BMR (41.7 kg/d) and leafy hybrid (42.1 kg/d) TMR were not different from each other in milk production, but had greater (P≤0.05) milk

1

To whom correspondence should be addressed: [email protected]

production than cows fed CONV1 (39.0 kg/d) or CONV2 (39.2 kg/d) hybrids. Greater intake by cows fed the BMR TMR than by cows fed the CONV1 or CONV2 TMR is likely the result of greater digestibility. Although the leafy hybrid TMR tended to be greater in digestibility than CONV1 or CONV2 TMR, it is likely that a lesser forage-toconcentrate ratio of the leafy hybrid TMR compared with the other TMR also contributed to its greater intake. Ruminal concentrations of propionate were greater in cows fed BMR than in those fed other hybrids, which could also result in greater milk production. Corn silage hybrids selected for improved forage quality can result in greater milk production by cows fed the improved hybrids in high forage diets. (Key Words: Corn Silage, Digestibility, Brown-Midrib, Leafy, Milk Production.)

Introduction Because of high farm land costs and sometimes limited land availability, dairy producers are faced with the challenge of harvesting the most milk production per acre of land. A variety of traits are being promoted for high milk production through improved forage quality. Digestible fiber is seen as increasingly important for its potential impact on DMI and milk pro-

duction (Tjardes et al., 2001). Two traits considered to improve fiber digestibility are the leafy and brown midrib (BMR) traits. A leafy hybrid was compared with a dual-purpose hybrid in total mixed rations (TMR); corn silage provided approximately 26% of the dietary DM (Thomas et al., 2001). The leafy hybrid had greater digestibility and resulted in greater milk production compared with the dual-purpose hybrid. Conversely, Bal et al. (2000a) compared conventional and leafy hybrids at two plant populations and reported no differences in milk production. A long history of BMR feeding trials vs normal counterparts for corn and sorghums also has resulted in inconclusive findings (Cherney et al., 1991). Decreased DM yield, despite improvements in fiber digestibility, resulted in generally unsatisfactory BMR performance in the past. Newer BMR varieties may have improved DM yields. Bal et al. (2000b) fed BMR vs normal corn silage and found lesser milk yield but greater milk fat percentage with the BMR silage. Ballard et al. (2001) compared three hybrids, including a BMR. The BMR silage yielded less, but was more digestible and had greater milk production than the leafy hybrid, but not greater milk production than a normal hybrid.

303

Corn Silage Hybrids for Dairy Cows

Cherney et al. (2002) reported an advantage to alfalfa-grass forage mixtures compared with pure alfalfa in high producing dairy cow diets, reinforcing the importance of the rest of the diet on overall results. Recent corn silage feeding trials have ranged from 26% corn silage in the diet (Thomas et al., 2001) to 70% corn silage in the diet (Barriere et al., 2001). It is possible to dilute the effects of a treatment based on its total contribution to dietary DM. Conversely, feeding corn silage at a greater rate than is normal may not be a reasonable comparison. Our goal was to compare corn silage treatments taking into account NDF content of corn silage when balancing diets with the corn silage component as a proportion of the total diet typically found in the Northeast. Our specific objective was to assess the impact of several corn silage traits on intake and milk production.

Materials and Methods Eight corn silage hybrids were grown at the Teaching and Research Center located near Harford, NY and harvested at a DM of about 34% in mid September 2002. Four of these hybrids were used in the feeding trial: a leafy hybrid (Mycogen TMF 100威; Mycogen Seeds, Indianapolis, IN), a BMR hybrid (Mycogen BMR F407威), and two hybrids differing in fiber digestibilities (Pioneer 36B08威 [digestible NDF = 57.8%], Conventional 1 [CONV1] and Pioneer 35P12威 [digestible NDF = 61.0%], Conventional 2 [CONV2]; Pioneer Hybrid International, Inc., Des Moines, IA). Diets were formulated to provide 1.0% BW as forage NDF (approximately 32% NDF). Diets were balanced to meet or exceed NRC requirements for lactating cows (Table 1). In addition to corn silage, alfalfa silage, high moisture corn, soybean meal, heat-treated soybean meal, and a protein-mineral-vitamin mix were used (Table 2). Diets were formulated using the Cornell Net Carbohydrate and Protein System (v5.25; Fox et al.,

TABLE 1. Formulated corn silage diet characteristicsa. Item Total DMI, kg/d CP, % of DM UIPc, % of CP Soluble CP, % of CP NDF, % of DM NFCc, % of DM Starch, % NEl, Mcal/kg Forage in diet, % F-NDFc, % of BW ME, Mcal/d MPc, g/d MP-bacteria, g MP-UIP, g ME milk, kg/d MP milk, kg/d

BMRb

Leafy

CONV1

CONV2

22.0 17.9 34 34 32.0 43 28.7 1.74 68 1.0 59.2 2640 1497 1143 38.8 40.3

22.0 18.9 34 36 33.0 41 27.9 1.76 61 1.0 59.9 2632 1444 1188 39.2 40.2

21.8 18.5 34 35 32.6 42 26.3 1.76 64 1.0 59.7 2630 1462 1168 39.2 40.3

22.0 18.1 33 37 32.0 43 29.3 1.76 67 1.0 59.8 2632 1504 1128 39.3 40.2

a Diets were evaluated using the Cornell Net Carbohydrate and Protein System (v5.25; Fox et al., 2000). b BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c UIP = Undegradable intake protein, NFC = non-fibrous carbohydrates, F-NDF = NDF from forage, and MP = metabolizable protein.

2000). Dry matter intake was targeted to be 22 kg/d for cows in midlactation and producing about 39 kg/d of milk. Fifty-six Holstein cows (504 ± 45.2 kg BW, 49 ± 9.3 kg/d milk yield, 1.9 ± 0.85 parity, and 84.4 ± 32.8 d in milk) were randomly assigned to treatment. Statistical design was a randomized complete block with 14 cows per treatment. Cows were housed in individual tie stalls throughout the experiment and had free access to water throughout the trial. Cows were offered a TMR fed for ad libitum intake once daily (1000 h) to allow for 10% orts. The TMR offered and orts were recorded daily. The trial was 56 d in duration, and data collection began on d 1. Feed offered and refused was recorded daily. The study had Cornell University Institutional Animal Care and Use Committee approval. All animals were used in compliance with Federal, state, and local laws and regu-

lations involving animal care and use, and the study was conducted in such a manner as to avoid unnecessary animal discomfort. Cows were milked three times daily (0800, 1600, and 0000 h). Milk yield was recorded daily. Milk was sampled once weekly at all three milkings and composited for each cow. Samples were preserved with 2-bromo-2-nitropropane-1, 3 diol. Samples were analyzed for fat, total protein, milk urea nitrogen, and lactose at the New York Dairy Herd Improvement milk testing laboratory (Ithaca, NY; infrared analysis: Foss 605B Milko-Scan; Floss Electric, Hillelrød, Denmark). Cows were weighed weekly beginning with the onset of the trial and concluding with the cessation of the trial. Body condition scores (five-point scale where 1 = thin to 5 = fat; [Wildman et al., 1982)]) were taken on the same day and time as cow BW.

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Diet and dietary ingredients were sampled weekly throughout the 56 d of the trial for DM (60°C, 48 h) determination. Diet forage-to-grain ratio was then adjusted as necessary. Representative samples of silages and TMR were analyzed by Dairy One (Dairy Herd Improvement Forage Testing Lab) for DM, CP, ADF, NDF, soluble protein, and non-structural carbohydrates (NSC). The NEl was estimated using the forage NEl variable discount method of Van Soest and Fox (1992). For these samples, DM was determined by drying at 135°C for 2 h (AOAC, 1990a). Nitrogen was determined by combustion (Leco Instruments, Inc., St. Joseph, MI) (AOAC, 1990c) and multiplied by 6.25 to obtain CP. Neutral detergent fiber, ADF, and sulfuric acid lignin were analyzed according to Van Soest et al. (1991) using the ANKOM system for NDF and ADF. Sulfite and heat-stable α-amylase were used for NDF analysis of all samples. Samples were not corrected to an ash-free basis. Soluble protein was determined using a sodium borate, sodium phosphate buffer procedure (Licitra et al., 1996). Acid detergent insoluble CP and neutral detergent insoluble CP (NDICP) were determined by subjecting fiber residues to Kjeldahl analysis to determine the protein fraction bound to fiber (Licitra et al., 1996). Sodium sulfite was not used for NDICP. Fat (ether extract) was determined using a Tecator Soxtec System. Ash was determined by dry combustion (AOAC, 1990b). Starch was determined using a YSI 2700 SELECT Biochemistry Analyzer (YSI Inc., Yellow Springs, OH). Sugar was determined using a watersoluble sugar method (Hall et al., 1999). The NSC was calculated as NSC = % starch + % sugar. The nonfibrous carbohydrate (NFC) was calculated as NFC = 100 − [% NDF + (% CP − % NDICP) + % fat + % ash] (NRC, 2001). Data were analyzed using repeated measures analysis models in the PROC MIXED procedure in SAS威, version 7.0 software (SAS Inst., Inc., Cary NC) according to Templeman and

Cherney et al.

Douglass (1999). The covariance structure with the best fit was AR (1), which is first-order autoregressive, and degrees of freedom were calculated using the Satterthwaite method. The statistical design was a continuous design with diet, week, and week × diet effects (day for milk production and intake). Week (day for intake and milk production) was repeated, and cow was considered random. Significance was P≤0.05 unless otherwise stated. The Tukey-Kramer procedure for multiple comparisons (P≤0.05) was used to test for differences among hybrids. Ruminal fluids from fistulated cows fed the corn hybrid TMR were sampled during this same time. Fistulated cows were housed randomly in the same barn as noted previously. They were milked and fed with the other experimental cows. The design for this study was an incomplete 4 × 4

Latin square (three periods) with one cow on each treatment per period. Periods consisted of a 14-d adjustment followed by 3 d of collection. Ruminal fluid was sampled 4 h after feeding for 3 consecutive d each period. Ruminal fluid pH was determined immediately. Samples were then frozen and sent to Dairy Herd Improvement Association for analysis of volatile fatty acids. Samples were analyzed for acetic, propionic, butyric, and iso-butyric acids using gas chromatography (Anonymous, 1990). Lactic acid was determined using a YSI 2700 SELECT Biochemistry Analyzer equipped with an L-lactate membrane. In vitro fiber digestibility and digestion kinetics of silages were determined according to Cherney et al. (1997) using the rumen buffer described by Marten and Barnes (1980) and using the Daisy II 200/220威 (ANKOM Technology Corp., Macedon,

TABLE 2. Ingredient composition of corn silage total mixed diet (% of DM)a. Item Corn silage Alfalfa silage High moisture corn SBM-48c Protein-mineral-vitamin mixd a

BMRb

Leafy

CONV1

CONV2

60.4 7.3 9.3 10.8 12.2

53.8 7.3 14.9 11.8 12.2

56.7 7.3 12.5 11.3 12.2

60.2 7.2 11.0 9.5 12.1

Forage was included in diet to provide 1.05% of cow BW as forage NDF. BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c SBM-48 = Soybean meal (48% CP). d Protein-mineral-vitamin mix from Agway, Inc., Syracuse, NY. Mix was 38.20% (minimum) CP (with not ≤12.2% equivalent CP from non-protein nitrogen), 0.80% crude fat (minimum), 13.50% crude fiber (maximum), 17.00% ADF (maximum), 3.55 % Ca (minimum), 4.55% Ca (maximum), 0.62 P (minimum), 2.19 ppm added Se (minimum) and 44,840 IU/kg vitamin A (minimum). Ingredients include plant protein products, roughage products, hydrolyzed poultry feathers meal, animal blood meal (conventional cooker dehydrated), methionine supplements, poly (2-vinylpryidine-co-styrene), calcium sulfate, ground limestone, salt, urea, monocalcium phosphate, magnesium oxide, calcium carbonate, sodium selenite, iron oxide, DL-methionine, corn starch, manganese sulfate, zinc sulfate, copper sulfate, ferrous sulfate, calcium iodate, cobalt sulfate, vitamin A supplement, vitamin D-3 supplement, and vitamin E supplement. b

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TABLE 3. Chemical analysis of total mixed rations (TMR; % of DM). Differences of least squares meansa

Item

BMRb BMR BMR Leafy Leafy CONV1 P≤c vs vs vs vs vs vs BMR Leafy CONV1 CONV2 SED leafy CONV1 CONV2 CONV1 CONV2 CONV2 Period

DM CP Soluble CP, % of CP ADF NDF NFCd NSCd Starch Sugar Fat TDN Lignin, % of NDF NDICPd, % of CP ADICPd, % of CP Ash

42.4 19.2 35.0 18.3 31.1 42.7 36.5 31.1 5.4 2.8 71.7 10.0 13.7 2.8 6.7

TMR

43.8 20.4 35.8 18.2 30.7 41.4 34.8 29.2 5.6 3.4 72.9 10.8 13.1 2.9 6.8

43.7 19.3 35.5 20.2 32.1 40.7 34.8 29.3 5.5 2.7 71.1 7.9 14.0 3.4 7.9

42.2 19.2 37.4 19.2 32.3 41.9 34.3 28.7 5.7 2.8 71.3 10.1 13.1 3.4 6.3

0.52 0.67 1.75 0.74 0.94 1.40 1.00 1.02 0.47 0.31 1.25 1.08 0.77 0.12 1.01

0.02 0.09 0.68 0.90 0.69 0.35 0.11 0.09 0.79 0.12 0.38 0.48 0.49 0.14 0.94

0.03 0.87 0.78 0.02 0.31 0.17 0.11 0.57 0.91 0.56 0.66 0.06 0.73 0.15 0.28

0.67 0.95 0.20 0.20 0.21 0.57 0.05 0.03 0.59 0.82 0.74 0.90 0.46 0.89 0.68

0.91 0.12 0.89 0.02 0.16 0.65 0.96 0.61 0.87 0.04 0.19 0.02 0.30 0.56 0.32

0.01 0.10 0.37 0.16 0.11 0.71 0.65 0.56 0.77 0.08 0.23 0.56 0.97 0.95 0.63

0.01 0.93 0.30 0.21 0.81 0.41 0.69 0.99 0.65 0.73 0.92 0.05 0.28 0.17 0.14

0.01 0.26 0.01 0.43 0.30 0.13 0.05 0.03 0.35 0.63 0.11 0.27 0.03 0.01 0.06

a

Paired comparisons between hybrids. BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c Significance of differences among weeks for the duration of the experiment. d NFC = Non-fibrous carbohydrates, NSC = non-structural carbohydrates, NDICP = neutral detergent insoluble CP, and ADICP = acid detergent insoluble CP. b

NY) in vitro incubator and the ANKOM 200/220威 fiber analyzer (ANKOM Technology Corp.). The buffer contained urea. Ruminal fluid inoculum was obtained from fistulated cows during d 14 of each period described previously. Duplicate samples (0.25 g) were incubated for 48 h at 39°C, followed by treatment of the undigested residue with neutral detergent solution. Incubation times for digestion kinetic determination were 0, 6, 9, 12, 24, 36, 48, 72, and 96 h. Estimates for kinetic parameters of digestion were determined using a direct nonlinear least squares estimating procedure using the Marquardt option of procedure NLIN in SAS. The model for kinetics of digestion was a simple first-order kinetic equation with a discrete lag time (Mertens and Loften, 1980). Data were analyzed using repeated measures analysis models in PROC MIXED in SAS, version 7.0 software, according to Templeman and

Douglass (1999). The design for this study was an incomplete 4 × 4 Latin square (three periods). Ruminal fluid was collected from the cow fed the Pioneer 35P12 diet each period; thus, period and diet of the cow were confounded.

Results and Discussion The four TMR were formulated to be similar in chemical composition and predicted daily milk yield (Table 1). This resulted in lesser forage in the diet for the leafy and CONV1 hybrids. Because alfalfa silage was included at a constant 7.3% of the diet, the lesser forage in the diets was accomplished through reductions in the corn silage (Table 2). High moisture corn accounted for the majority of the increase in concentrate. We formulated diets to be greater than NRC (2001) recommendations for CP to en-

sure that responses would not be limited by ruminal NH3. Crude protein, soluble CP, NDF, and NFC of actual TMR fed were similar to what we formulated (Table 3).The NSC were greater in the BMR TMR than in CONV2 TMR (P≤0.05). Starch tended to be greater in actual TMR than was formulated. In general, the four TMR were very similar in chemical composition. Dry matter was slightly greater in the leafy and CONV1 TMR. The greater DM would be expected, as the leafy and CONV1 TMR had slightly less forage-to-concentrate ratios than the BMR and CONV2 TMR (Table 3). The CONV1 TMR was slightly greater (P≤0.02) in ADF than the BMR and leafy TMR. The lignin content, expressed as a percentage of NDF, was less in the CONV1 TMR than in the CONV2 and leafy TMR (Table 3). This was due to not only the lesser forage-toconcentrate ratio of the CONV1

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TABLE 4. Chemical and fementation analysis of silages. Differences of least squares meansa Silage Item

BMR Leafy CONV1 CONV2

SED

Chemical analyses DM CP Soluble CP, % of CP ADF NDF NFCd NSCd Starch Sugar Lignin NEl TDN Crude fat Ash Fermentation analyses pH Ammonia, % Lactic acid (L), % Acetic acid (A), % L:A Total acids, %

BMRb BMR BMR Leafy Leafy CONV1 P≤c vs vs vs vs vs vs leafy CONV1 CONV2 CONV1 CONV2 CONV2 Period (% of DM)

32.9 8.4 51.2 22.8 40.3 43.6 38.8 35.0 3.7 2.15 0.75 71.5 3.4 3.3

32.8 8.6 58.8 24.4 44.5 39.6 35.0 29.8 5.2 3.0 0.72 70.0 3.2 3.1

32.7 8.3 59.3 25.2 44.7 39.8 34.0 30.5 3.5 2.4 0.72 70.3 3.1 2.6

32.5 8.8 58.7 24.5 43.7 40.4 33.9 28.9 4.9 3.0 0.72 70.0 3.0 2.8

0.59 0.18 1.57 0.93 0.06 1.38 2.02 1.99 0.27 0.18 0.012 0.63 0.19 0.19

0.81 0.48 0.01 0.12 0.02 0.02 0.08 0.02 0.01 0.02 0.02 0.04 0.38 0.53

0.74 .56 0.01 0.03 0.65 0.02 0.04 0.04 0.44 0.26 0.04 0.09 0.17 0.05

0.45 0.23 0.01 0.09 0.03 0.04 0.03 0.01 0.01 0.02 0.02 0.04 0.11 0.10

0.94 0.21 0.75 0.42 0.41 0.88 0.63 0.72 0.01 0.04 0.68 0.61 0.50 0.08

0.62 0.61 0.92 0.89 0.54 0.58 0.58 0.66 0.37 0.99 0.89 0.99 0.29 0.19

0.68 0.09 0.68 0.50 0.87 0.68 0.94 0.44 0.01 0.04 0.58 0.61 0.64 0.39

0.20 0.18 0.01 0.03 0.75 0.25 0.67 0.54 0.01 0.39 0.06 0.01 0.99 0.73

3.65 0.61 6.4 1.1 5.9 7.50

3.68 0.68 6.7 0.9 7.0 7.62

3.58 0.68 7.3 1.2 6.3 8.46

3.67 0.68 7.5 1.0 7.8 8.55

0.050 0.025 0.33 0.08 0.01 0.308

0.51 0.02 0.39 0.05 0.48 0.70

0.20 0.02 0.02 0.54 0.22 0.01

0.74 0.03 0.01 0.10 0.07 0.01

0.07 0.95 0.07 0.02 0.63 0.02

0.74 0.85 0.02 0.71 0.03 0.01

0.12 0.90 0.49 0.03 0.23 0.80

0.01 0.06 0.01 0.32 0.29 0.01

a

Paired comparisons between hybrids. BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c Significance of differences among weeks for the duration of the experiment. d NFC = Non-fibrous carbohydrates; NSC = non-structural carbohydrates. b

TMR, but also to the fact that the CONV1 silage contained less lignin than the CONV2 and leafy silages (Table 4). Daily milk production was greater for cows fed the leafy TMR than for those fed either of the conventional hybrid diets, and milk production of cows fed the BMR TMR tended to be greater than that for cows fed the conventional hybrid TMR (Table 5). There was an effect of day (Table 5), but, in general, cows fed the conventional TMR did not produce as much milk as those fed the BMR and leafy TMR (Figure 1). Dry matter intake generally followed milk production (Table 5) and likely accounted for some of the differences observed in

milk production. There was a significant effect of day and a day × hybrid interaction (P≤0.01). As with milk production, cows fed the BMR and leafy TMR had generally greater intakes than those fed the conventional TMR (Figure 2). Greater DMI can result from greater digestibility, greater rate of digestion, and/or faster rate of passage. In our study, the BMR silage had greater in vitro true digestibility (IVTD) than the other hybrids (P≤0.05) at all time points (Figure 3). The leafy silage tended to be greater in IVTD than the conventional hybrids, but was generally less than the BMR silage. Although not significant (P>0.05), the IVTD of the CONV1 tended to be less

than all other hybrids. Oba and Allen (1999) suggested that increased NDF digestibility would increase DMI. Our data support this conclusion for BMR silage, in that BMR silage had the greatest digestible NDF from 30 h on (Figure 4). The leafy hybrid, although numerically greater than the conventional hybrids, was not significantly greater than the other hybrids. Cows fed a diet high in NDF digestibility had greater DMI than those fed a lesser digestible diet (Robinson and McQueen, 1997). Oba and Allen (1999) and Cherney et al. (2004) also reported that enhanced NDF digestibility increased DMI. In addition, Ketelaars and Tolkamp (1992) suggested that greater quality forage increased

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TABLE 5. Influence of diet on intake and milk production. Item

Milk

SEMa

DMI

SEM

BMRb Leafy CONV1 CONV2

41.7 42.1 39.0 39.2

0.95 0.91 0.98 0.98

22.7 22.9 21.8 20.9

(kg/d) 0.40 0.44 0.42 0.43

Hybrid Week Hybrid × week

0.05 0.01 0.07

NDF intake

SEM

NDF intake

SEM

7.0 7.0 6.9 6.7

0.10 0.09 0.10 0.10

(% of BW) 1.38 1.41 1.43 1.31

0.035 0.033 0.037 0.036

P
0.01 0.01 0.01

0.08 0.01 0.01

Comparison between hybrids (P<)

BMR vs leafy BMR vs CONV1 BMR vs CONV2 Leafy vs CONV1 Leafy vs CONV2 CONV1 vs CONV2

Milk (kg/d)

SEDd

DMI (kg/d)

SED

NDF intake (kg/d)

SED

NDF intake (% BW)

SED

0.76 0.06 0.08 0.03 0.04 0.88

1.32 1.36 1.36 1.33 1.34 1.38

0.81 0.11 0.01 0.07 0.01 0.14

0.56 0.58 0.59 0.57 0.58 0.60

0.85 0.90 0.44 0.76 0.33 0.52

0.29 0.30 0.30 0.29 0.29 0.30

0.47 0.23 0.18 0.59 0.04 0.02

0.048 0.051 0.050 0.050 0.049 0.06

a

Standard error of the mean. BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c Probability coefficient for model effects. d Standard error of the difference. b

Figure 1. Milk production per day for cow diets containing four corn silage hybrids: Brown midrib = Mycogen BMR F407威 (Mycogen Seeds, Indianapolis, IN; 䊉; SEM = 2.1), leafy = Mycogen TMF 100威 (Mycogen Seeds; ▼; SEM = 2.0), conventional hybrid 1 = Pioneer 36B08威(Pioneer Hybrid International, Inc., Des Moines, IA; 䉮; SEM = 2.1), and conventional hybrid 2 = Pioneer 35P12威 (Pioneer Hybrid International, Inc.; 䊊; SEM = 2.2).

the rate of passage of indigestible fiber. In our study, BMR had less indigestible residues than the other silages and a greater extent of NDF digestion; the leafy hybrid tended to have less indigestible residues than CONV1 (Table 6), which would further account for the differences in DMI observed in this study. Because DMI was as high or greater by cows fed leafy TMR as compared with those fed the BMR TMR, differences in digestible NDF are not likely to account for all differences in DMI. Concentrates typically increase milk production by allowing for greater DMI (Weiss, 1995; Robinson and McQueen, 1997, Cherney et al. 2002); it is likely that this contributed to greater milk production of cows fed the leafy TMR. Milk fat and lactose percentages were not influenced by corn silage hybrid (Table 7). There was some week-to-week variation, but no hy-

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Cherney et al.

Figure 2. Dry matter intake per day for cows fed diets containing four corn silage hybrids: brown midrib = Mycogen BMR F407威 (Mycogen Seeds, Indianapolis, IN; 䊉; SEM = 0.89), leafy = Mycogen TMF 100威 (Mycogen Seeds; ▼; SEM = 0.86), conventional hybrid 1 = Pioneer 36B08威(Pioneer Hybrid International, Inc., Des Moines, IA; 䉮; SEM = 0.93), and conventional hybrid 2 = Pioneer 35P12威 (Pioneer Hybrid International, Inc.; 䊊; SEM = 0.95).

brid × week interaction for these components. Milk true protein was greater for cows fed the BMR TMR than for cows fed the CONV2 TMR (P≤0.03) and tended to be greater than that for cows fed the leafy TMR (P≤0.06), probably because of the greater NSC content of the BMR TMR. Ruiz et al. (1995) reported that milk true protein increased with increasing NFC. The

milk urea nitrogen of cows fed the BMR TMR was less than that for cows fed the other TMR, significantly for the leafy and CONV1 TMR (Table 7). Ruminal pH was least in fistulated cows fed BMR and CONV1 TMR and greatest in those fed the leafy TMR (Table 8). There was a period effect; Period 2 was greater than Period 1 (Table 6), most likely

because of the addition of the sodium bicarbonate to all TMR at d 21. Low ruminal fluid pH of sampled cows prompted health concerns for the cows. To not jeopardize the welfare of the cows, about 0.1 kg/d of sodium bicarbonate was added to all diets. Low ruminal pH in cows fed corn silage is consistent with results reported previously (Greenfield et al., 2001). Lesser ruminal pH in cows fed CONV1 is consistent with those cows, which were fed the least forage-to-concentrate ratio. Ruminal acetate concentrations did not change in response to TMR (P>0.05; Table 8). Ruminal concentrations of propionate were greater in cows fed BMR than in those fed other hybrids (Table 8). Greenfield et al. (2001) reported greater propionate concentrations in cows fed BMR silage. Butyrate concentrations were numerically least in cows fed BMR, although this was significantly less only with butyrate concentrations for cows fed CONV2 TMR. There were no differences in total acids or acetate-topropionate ratios among cows fed the different hybrids (Table 8). A greater ruminal propionate concentration in BMR-fed cows could be

TABLE 6. Digestion kinetics as influenced by silage. Differences of least squares meansa Silage Item d

Do , % of DM kd lagd, h IRd, % of DM Extentd, % of NDF a

BMR

Leafy

25.4 0.0598 10.5 13.3 65.8

25.6 0.0585 10.0 17.8 58.8

CONV1 CONV2 20.8 0.0706 11.0 21.6 48.9

22.7 0.0720 12.1 19.9 53.3

SED 1.51 0.00040 0.80 1.09 3.00

BMRb BMR BMR Leafy Leafy CONV1 P≤c vs vs vs vs vs vs leafy CONV1 CONV2 CONV1 CONV2 CONV2 Period 0.99 0.99 0.90 0.02 0.19

0.08 0.12 0.93 0.01 0.01

0.37 0.09 0.29 0.01 0.03

0.07 0.08 0.61 0.06 0.06

0.31 0.06 0.13 0.35 0.35

0.62 0.98 0.55 0.47 0.52

0.78 0.03 0.03 0.53 0.94

Paired comparisons between hybrids. BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c Significance of differences among weeks for the duration of the experiment. d Do = Potentially digestible residue at time = 0, k = rate of digestion, lag = time before digestion begins, IR = indigestible residue (NDF − d0), and extent = (d0/NDF) × 100. b

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Corn Silage Hybrids for Dairy Cows

TABLE 7. Influence of diet on milk components. Item

Milk fat

SEMa

Milk protein

0.078 0.075 0.080 0.081

2.87 2.74 2.77 2.71

(%) BMRc Leafy CONV1 CONV2

3.26 3.30 3.32 3.28

SEM

MUNb

SEM

Lactose

0.048 0.047 0.049 0.050

(mg/dL) 12.6 14.0 14.1 13.5

0.37 0.36 0.38 0.38

4.78 4.67 4.69 4.68

(%)

SEM

(%) 0.043 0.042 0.044 0.044

P
BMR vs leafy BMR vs CONV1 BMR vs CONV2 Leafy vs CONV1 Leafy vs CONV2 CONV1 vs CONV2

0.95 0.01 0.89

0.11 0.01 0.02

0.03 0.01 0.07 Comparison between hybrids (P<)

0.23 0.01 0.09

Milk fat (%)

SEDe

Milk protein (%)

SED

MUN (mg/dL)

SED

Lactose (%)

SED

0.72 0.56 0.83 0.82 0.89 0.72

0.108 0.111 0.112 0.110 0.111 0.114

0.06 0.16 0.03 0.63 0.66 0.37

0.067 0.069 0.069 0.068 0.068 0.070

0.02 0.01 0.09 0.76 0.44 0.30

0.53 0.55 0.55 0.54 0.54 0.55

0.06 0.17 0.10 0.64 0.83 0.80

0.060 0.062 0.061 0.060 0.062

a

Standard error of the mean. MUN = Milk urea nitrogen. c BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). d Probability coefficient for model effects. e Standard error of the difference. b

TABLE 8. Influence of diet on ruminal pH and volatile fatty acids. Differences of least square meansa BMRb BMR BMR Leafy Leafy CONV1 P≤c vs vs vs vs vs vs Leafy CONV1 CONV2 SED leafy CONV1 CONV2 CONV1 CONV2 CONV2 Period Silage

Item

BMR

pH 5.3 5.5 5.3 5.4 Acetate:propionate ratio 1.87 2.22 2.17 2.11 Acetate, mmol/L 77.3 77.1 76.6 77.4 Propionate, mmol/L 44.1 35.4 37.0 38.5 Butyrate, mmol/L 18.4 20.7 19.1 22.0 Total acids, mmol/Ld 142.7 136.1 135.7 140.8 a

0.05 0.15 2.11 1.75 0.75 3.10

0.01 0.19 0.95 0.02 0.11 0.23

0.86 0.20 0.81 0.03 0.54 0.15

0.21 0.28 0.98 0.06 0.02 0.68

0.01 0.84 0.87 0.54 0.19 0.92

0.02 0.28 0.91 0.25 0.26 0.32

0.29 0.64 0.81 0.61 0.05 0.34

0.01 0.10 0.07 0.15 0.05 0.26

Paired comparisons between hybrids. BMR = Brown midrib hybrid (Mycogen F407BMR威; Mycogen Seeds, Indianapolis, IN), leafy = Mycogen TMF100威 (Mycogen Seeds); CONV1 = conventional hybrid 1 (Pioneer 36B08威; Pioneer Hybrid International, Inc., Des Moines, IA), and CONV2 = conventional hybrid 2 (Pioneer 35P12威; Pioneer Hybrid International, Inc.). c Significance of differences among weeks for the duration of the experiment. d Total acids = acetate + propionate + butyrate + lactate + iso-butyrate (mmol concentrations). b

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Cherney et al.

Figure 3. In vitro DM digestibility (IVTD; %) for diets containing four corn silage hybrids: Brown midrib = Mycogen BMR F407威 (Mycogen Seeds, Indianapolis, IN; 䊉), leafy = Mycogen TMF 100威 (Mycogen Seeds; ▼), conventional hybrid 1 = Pioneer 36B08威(Pioneer Hybrid International, Inc., Des Moines, IA; 䉮), and conventional hybrid 2 = Pioneer 35P12威 (Pioneer Hybrid International, Inc.; 䊊).

the result of the greater starch concentration of the BMR silage. Greater starch in the diet usually results in more propionate production, which could also result in greater milk production.

Implications Because of high farm land costs, dairy producers are faced with the challenge of harvesting the most

Figure 4. Digestible NDF (dNDF; %) for diets containing four corn silage hybrids: Brown midrib = Mycogen BMR F407威 (Mycogen Seeds, Indianapolis, IN; 䊉), leafy = Mycogen TMF 100威 (Mycogen Seeds; ▼), conventional hybrid 1 = Pioneer 36B08威(Pioneer Hybrid International, Inc., Des Moines, IA; 䉮), and conventional hybrid 2 = Pioneer 35P12威 (Pioneer Hybrid International, Inc.; 䊊).

milk production per acre of land. Hybrids selected for improved forage quality traits, such as BMR and leafy, should result in greater DMI and milk production. Improved forage quality is not without cost, however. The BMR hybrids typically produce 10 to 15% lesser yields than normal hybrids and also exhibit more stress under marginal environmental conditions (Cox and Cherney, 2001). Greater seed costs also are generally associated with improved hybrids. Dairy producers must evaluate the benefits and risks associated with improved forage quality varieties. The results of this trial will help dairy producers decide the cost effectiveness of using more digestible forages.

Acknowledgments This research was supported in part by the Cornell University Agricultural Experiment Station federal formula funds, Project No. NYC-1277431, received from Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture, and in part by the Northeast Dairy Producers Association. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the U.S. Department of Agriculture. This study would not have been possible without the assistance of the staff of the Cornell University Teaching and Research Facility. The assistance of Gladys Birdsall, Samuel Beer, and Agripina Gonzales is especially appreciated.

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