The Corn Feed

Here are some of the latest research findings pertaining to silage and dairy production presented at the 2011 American Dairy Science Association/American Society of Animal Science Joint Annual Meeting in New Orleans, La.:

M319 Independent effects of diet chemical fiber and physical measurements on dairy cows

D. Sauvant, W. Z. Yang, D. R. Mertens and K. A. Beauchemin

Fiber effectiveness has been defined by physically effective neutral detergent fiber (peNDF), which is the product of neutral detergent fiber (NDF) and the fraction retained on a 1.18-mm sieve. To evaluate the concept of using an index (product of fiber and particle size) for predicting cow responses, a meta-analysis was performed to assess the independent and interaction effects of chemical fiber (NDF) and alternative physical measurements (PM). A database was compiled from 24 published experiments using lactating dairy cows and 104 (n) treatments where dietary NDF and PM were reported. Forages were long, chopped or grounded. Dietary NDF averaged 35.3 ± 7.1 percent of dry matter (DM). Three PM were considered: mean particle size (MPS; 3.72 ± 2.02 mm, n = 44), particles retained on a 2-mm sieve (P2; 42.4 ± 15.5 percent DM, n = 40) or on 19-mm and 8-mm sieves of the Penn State Particle Separator (P8; 49.5 ± 12.7 percent DM, n = 36). As the PM was not measured with the same criteria across the experiments, a dummy variable (0 or 1) was created to systematically code the short or long PM, respectively. The effects of NDF and PM were tested on chewing index (CI; 37.5 ± 11.9 min/kg DMI, n = 78), rumen pH (6.08 ± 0.26, n = 60), acetate to propionate ratio (A:P; 2.70 ± 0.73, n = 52), milk yield (MY; 29.0 ± 10.6 kg/d, n = 96) and milk fat percentage (MF; 3.75 ± 0.62 percent, n = 82). Meta-analyses were carried out using GLM procedure including the effects of experiment, NDF, PM and the interaction. NDF was a continuous co-variable. The mean differences between treatments were: NDF = 4.3 percent DM; MPS = 1.31 mm; P2 = 7.5 percent DM; and P8 = 8.6 percent DM. Experiment was systematically significant (P < 0.01). For CI, pH and A:P, influences of NDF and PM were significant (P < 0.01), but there was no interaction between them. For MY and MF, only the effect of NDF was significant (P < 0.01). As expected, MF was negatively affected (P < 0.01) by pH (MF = −1.05 + 0.76 pH, n = 48, RMSE = 0.05 percent). In conclusion, the effects of NDF and PM appeared to be additive in published trials, which questions the principle and the validity of their product (peNDF) for predicting lactating cow responses.

82 Production response to corn silage produced from normal, brown midrib or waxy corn hybrids

J. S. Barlow, J. K. Bernard and N. A. Mullis

The starch in waxy corn hybrids is 100 percent amylopectin, which has been suggested to be more digestible than that of normal corn hybrids, but the production response to feeding silage produced from these hybrids has been inconsistent. In contrast, brown midrib (BMR) corn varieties have lower lignin concentrations and have been shown to support higher dry matter intake (DMI) and milk yield. The objective of this study was to evaluate the nutrient intake and milk production response of lactating dairy cows to diets based on corn silage produced from three different types of corn hybrids. Thirty-six multiparous and primiparous Holstein cows (77 DIM and 37.1 kg/d milk) were used in an 11-week completely randomized design trial during the fall of 2009. Experimental diets contained 36.4 percent of the dietary dry matter (DM) from corn silage from either a normal (Agratech 1021), BMR (Mycogen F2F797) or waxy (Master’s Choice 590) hybrid. All cows were fed the diet containing normal corn silage during the first two weeks of the trial before being assigned to one of three treatments for the following nine weeks. Data collected during the first two weeks were used as a covariate in the statistical analysis. No difference (P = 0.81) was observed in DMI among treatments which averaged 22.6 kg/d. Milk yield was highest (P = 0.03) for cows fed BMR (37.6 kg/d) compared with waxy (35.2 kg/d) but similar to control (36.2 kg/d). Milk fat percentage tended to be lower (P = 0.10) for cows fed control (3.28 percent) compared with BMR (3.60 percent) or waxy (3.55 percent) corn silage. Milk protein percentage (P = 0.07) tended to be lower for cows fed normal (2.79 percent) compared with waxy (2.89 percent) but similar to BMR (2.85 percent). No differences were observed in yield of milk components. Energy-corrected-milk (ECM) yield, dairy efficiency (ECM/DMI) and body weight change did not differ among treatments. Results of this trial are consistent with previous reports in which cows fed diets based on corn silage produced from BMR hybrids have higher milk yield compared with other hybrids. Corn silage produced from the waxy hybrid supported similar yield of ECM because of higher milk components, but milk yield was not improved compared with the normal.

146 Spoilage yeasts in silage have the potential to directly impact rumen fermentation

M. C. Santos, A. L. Lock, G. D. Mechor and L. Kung Jr.

Yeasts associated with aerobic spoilage of high-moisture corn (HMC) and corn silage (CS) were isolated and characterized to determine their potential for direct effects on rumen fermentation. Samples were obtained from 21 U.S. dairy farms; HMC averaged 6.3 and CS averaged 5.4 log₁₀cfu of yeasts/g of fresh forage. Candida valida (CV) was the most predominant species accounting for 35 and 31 percent of total isolates in HMC and CS, respectively. One isolate of CV was added to in vitro culture tubes containing total mixed ration (TMR), buffer and rumen fluid at theoretical concentrations of 0, 4.4, 6.4 and 8.4 log₁₀cfu/ml; the 6.4 dose was equivalent to a cow consuming 30 kg of fresh CS with 7.0 log₁₀cfu/g. After 12 and 24 hours of incubation at 39°C, samples were analyzed for pH, yeast number, neutral detergent fiber digestibility (NDF-D), volatile fatty acids (VFA) and fatty acids (FA). Culture pH declined from 6.8 at 0 hours to 6.4 and 6.3 after 12 and 24 hours, respectively (P < 0.01). After 24 hours, numbers of viable yeasts for the control treatment decreased from 2.4 to 0.4 log₁₀cfu/ml. For the other levels, the measured numbers at time zero decreased from 4.0, 5.9 and 8.1 to 2.2, 3.9 and 5.3 log₁₀cfu/ml after 24 hours, respectively. Inoculation with CV caused a linear decrease in NDF-D at 12 and 24 hours (P < 0.01). After 12 hours, NDF-D for the highest CV addition was 34 versus 44 percent for control and after 24 hours NDF-D was 52 versus 58 percent. At 24 hours, the concentration of total VFA, acetate and propionate was 106, 57 and 29 mM for the highest CV dose whereas for control the concentrations were 98, 53 and 25 mM, respectively (P < 0.05). FA analysis of CV indicated that it contained ~25 percent saturated fatty acids (SFA), 60 percent cis monounsaturated fatty acids, and 15 percent cis polyunsaturated fatty acids. Overall, the biohydrogenation (BH) of unsaturated FA was not altered across treatments and declined over time with an increase in the accumulation of SFA, especially stearic acid; under the conditions tested, CV did not alter the formation of BH intermediates. The results of this study indicate that the addition of CV, especially in high levels, can decrease NDF-D and may alter the concentration of propionate and acetate. However, no changes in the production of BH intermediates were detected under the in vitro conditions tested.

T122 Relationships of fermentation characteristics in corn forage

R. Ward and D. R. Mertens

Our objective was to study factors affecting the fermentation characteristics of corn forage using a database of analyses from Cumberland Valley Analytical Services, Inc. The initial database contained 4,712 samples over four years from 41 states with analyses including fermentation characteristics such as titratible acidity (TA), ammonia (NH₃), acetic (Ac), lactic (La), and propionic (Pr) acids (measured chemically). Components such as dry matter (DM), crude protein (CP), ash, neutral detergent fiber (NDF), acid detergent lignin (ADL), starch (St) and sugar (Su) were determined by chemical or NIR methods. Non-ammonia N (NAN) was calculated by difference between CP and NH₃. Data was analyzed using Proc MIXED in SAS. In order, TA was affected by Ac, La, Pr, NAN, St, Su, NH₃, ash and ADL (P < 0.0001). Intercept, Ac and La accounted for 0.61, 0.20 and 0.18, respectively, of the variation explained by the model. The coefficients for Ac, La and Pr were positive and all other variables had negative coefficients. Average TA was 7.2 in October, increased to 8.0 by January and was maximum (8.9) in April (all different P < 0.005). Corn silage NH₃ (percent DM) was related (in order) to Ac, La, CP, St, ADL and Pr (R² = 0.54). Intercept, Ac and La accounted for 0.40, 0.22 and 0.19 of model variation, respectively. All coefficients were positive. Average NH₃ was 0.77 in October increased to 0.90 by January and was maximum (1.08) in May (all different P < 0.0001). When TA replaced individual acids (La, Ac, Pr) in the model, NH₃ was related (in order) to TA, CP, St and ADL (R² = 0.52); TA accounted for 0.73 of model variation. Expressing NH₃ as percent of CP reduced the R² (= 0.45) and the influence of CP (P = 0.093). When months in storage was added to the NH₃ model with TA, CP, St and ADL, the R² increased to 0.56, and the linear and quadratic effects of storage were significant (P < 0.0001). When Ac was grouped by level, DM, St and Su decreased, and fiber and NH₃ increased, as group Ac increased. Region or year had limited effects on any of the results. We concluded that NH₃ in fermented corn forage is related not only to the extent of fermentation as indicated by TA or acids (Ac, La, Pr), but also to time in storage. Fermentation relationships can explain changes in corn forage that affect utilization.