Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/23/1997
Publication Date: N/A
Citation: Interpretive Summary: In the U.S., most alfalfa is fed to dairy cows as silage because harvesting silage requires much less manual labor than harvesting hay. However, the protein in alfalfa silage is subject to extensive breakdown in the rumen, the first compartment of the cow's stomach. The rumen microbes both form and degrade protein; they reduce the value of the protein in alfalfa silage eby forming less protein than they degrade. Dietary energy stimulates protein formation by the rumen microbes. High moisture corn is one of the principal energy sources fed to dairy cows in the U.S. There is a major controversy about whether processing of high moisture corn increases its energy availability enough to improve protein formation in the rumen and milk and protein yield in the cow. A feeding trial was conducted to test the value of grinding of high moisture corn fed with alfalfa silage. Four diets were fed: two with conventional high moisture corn and two with high moisture corn that was ground through a 3/8 inch screen. One diet with eac type of corn was supplemented with a protein known to escape breakdown in the rumen and one diet was not. All diets contained the same level of alfalfa silage as the sole forage. Feeding added protein increased milk and protein yield on both types of high moisture corn. Grinding was 64% as effective as feeding protein in increasing milk yield and 100% as effective in increasing protein yield. A laboratory trial conducted with rumen fluid confirmed that grinding increased rate of digestion and protein formation by the rumen microbes. Grinding of high moisture corn, an effective strategy for improving milk and protein yield of dairy cows fed alfalfa sileage, can be used by farmers to increase utilization of protein and reduce the amount of nitrogen lost to the environment.
Technical Abstract: Thirty-six multiparous (eight with ruminal cannulae) and 16 primiparous dairy cows were blocked by DIM and parity and assigned to one of four TMR containing 53% (DM basis) alfalfa silage plus: 1) high moisture ear corn; 2) high moisture ear corn + expeller soybean meal; 3) ground high moisture ear corn; 4) ground high moisture ear corn + expeller soybean meal. The high moisture ear corn was rolled before ensiling at 68% DM; ground high moisture ear corn was prepared by grinding through a 9.5 mm screen. Grinding reduced geometric mean particle size of high moisture ear corn from 4.33 to 1.66 mm. Diets contained 1.69 Mcal NEL/kg DM. Relative to diet 1, milk yield was 4 kg/d greater for diet 2 and about 2 kg/d greater for diets 3 and 4. Yield of milk components also was greater on diets 2 and 3, but not on diet 4. Dry matter intake and yield of 4% FCM was greatest in cows fed diet 3 and lowest in cows fed diet 1. Digestibilities of DM, OM, starch, NDF, and ADF were increased, and ruminal ammonia concentration depressed, by grinding of high moisture corn; feeding expeller soybean meal increased ruminal ammonia. Total VFA concentration was not different among treatments but molar proportion of acetate decreased and propionate increased on diet 3. Grinding of high moisture corn significantly decreased pH, increased total VFA concentration and increased the rate of decline of ammonia concentration in ruminal in vitro incubations. Grinding improved utilization of high moisture corn by lactating cows by stimulating ruminal fermentation.