Submitted to: Animal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/26/2011
Publication Date: 4/1/2012
Publication URL: http://handle.nal.usda.gov/10113/56948
Citation: Krizsan, S.J., Broderick, G.A., Promkot, C., Colombini, S. 2012. Effects of alfalfa silage storage structure and roasting corn on ruminal digestion and microbial CP synthesis in lactating dairy cows. Animal. 6:624-632. Interpretive Summary: In the U.S., alfalfa usually is fed to dairy cows as silage rather than hay because harvesting silage is much more rapid and requires less manual labor. Among the common silo structures used to ensile alfalfa are plastic bags, bunkers and oxygen-limiting silos. However, it is not known whether there is a clear advantage to using any one of these 3 different silos for conserving the feeding value of alfalfa. Moreover, there is an additional problem with alfalfa silage in that its protein is extensively degraded in the rumen, the first compartment of the cow's stomach. Microbes in the rumen both form and degrade protein, but they usually reduce the value of protein in alfalfa silage because they form less protein than they degrade. Dietary energy stimulates the rumen microbes to form more protein. Corn grain is the principal dietary energy supplement fed to U.S. dairy cows; heating corn increases its rate of digestion in nonruminants. This study examined whether feeding roasted corn as the energy supplement for cows eating alfalfa ensiled in plastic bags, bunkers or oxygen-limiting silos would improve digestion or microbial protein formation in the rumen. Results indicate a small increase in energy digestion in the rumen when cows were fed diets containing roasted corn; however, no differences were discovered in microbial protein formation due to roasting corn or due to feeding any of the different silages. Fiber digestion in the rumen was lower in cows fed alfalfa silage from the bunker versus the bag and oxygen-limiting silos. Also, there was reduced wastage of silage from the oxygen-limiting silo versus the other 2 silos. These results indicate that ensiling alfalfa in the oxygen-limiting silo would improve recovery of alfalfa’s nutrients, as well as rumen fiber digestion in dairy cows. Greater milk yield per unit feed consumed would mean better protein utilization and reduced nitrogen pollution in the environment, but the economic advantage to the dairy farmer depends on the relative cost of the silos. Because the small increases in energy value gained by roasting corn was not enough to pay for the fuel and equipment, these results indicated that corn roasting would not result in an economic or environmental advantage for dairy farmers.
Technical Abstract: The objective of this experiment was to determine the effects of unroasted ground shelled corn (GSC) or roasted GSC (RGSC), when fed with alfalfa, ensiled in bag, bunker, or O2-limiting tower silos on ruminal digestion and microbial protein synthesis in lactating dairy cows. The roasted corn was heat-treated in a propane-fired roasting system. Alfalfa was harvested as second cutting from fields with regrowth of the same maturity. A portion of each field was allotted to each silo. The diets with a 3 x 2 factorial arrangement of treatments were fed to 6 multiparous Holstein cows in a cyclic change-over design with five 21-d periods. Experimental diets were comparable and averaged (on dry matter basis): 41% alfalfa silage (AS), 15% corn silage, 35% ground shelled corn, 5% soybean meal, 4% roasted soybeans, 17.7% crude protein, 26.4% neutral detergent fiber, and 25.0% starch. Nutrient flow was quantified by the omasal sampling technique with use of three markers (Co + Yb + indigestible neutral detergent fiber). Continuous infusion of 10% atom excess (15NH4)2SO4 was used to label microbial protein. None of the interactions between storage structure of dietary AS and corn type was significant. Dry matter intake and omasal flow were not different among dietary treatments, averaging 24.5 and 17.0 kg/d across diets. Dry matter and OM apparently digested in the rumen were 1.48 and 1.38 kg/d higher, respectively, for cows fed RGSC than cows fed GSC. The means of acid detergent fiber apparently digested in the rumen for cows fed diets with AS from bag, bunker, and O2-limiting silo were 2.08, 1.69, and 2.10 kg/d, respectively, and was lower in cows fed AS from the bunker silo. The results from the previous companion trial showed that feeding AS from the O2-limiting tower silo resulted in greater yields of fat and 3.5% fat-corrected milk, which is in agreement with the increased ruminal digestibility of acid detergent fiber in this trial. Small increases in yield of milk protein and lactose observed in the production trial of cows fed RGSC were explained by greater supply of fermentable substrates on those diets.