Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/21/2006
Publication Date: 10/1/2006
Citation: Brito, A.F., Broderick, G.A. 2006. Effect of varying dietary ratios of alfalfa silage to corn silage on production and nitrogen utilization in lactating dairy cows. Journal of Dairy Science. 89:3924-3938. Interpretive Summary: Alfalfa silage is high in total protein but this protein is very degradable in the rumen. Corn silage, although low in total protein, is high in rumen-available energy. This makes these forages potentially complementary feedstuffs that could work well together in diets fed to dairy cows. To help determine the optimal level of each for milk production and feed utilization, 28 Holstein cows were fed diets containing four different ratios of alfalfa silage to corn silage, 51:0, 37:13, 24:27, and 10:40. Soybean meal was added as alfalfa was decreased to maintain similar total protein in the diet and high moisture corn (a major feed ingredient fed to US dairy cows) made up most of the rest of diet. Feed intake, yield of milk and fat, and fiber digestibility all decreased when corn silage replaced alfalfa silage in the diet. Fiber digestion may have fallen because the rumen (the first compartment of the cow’s stomach) was too acid when insufficient alfalfa was fed. Protein efficiency improved when corn silage plus soybean meal replaced some of the dietary alfalfa silage because the cows excreted less urinary nitrogen (the form of excretory nitrogen that is most polluting to the environment). However, milk protein yield eventually declined when too much corn silage was fed. This research showed that milk and protein yield were highest on diets containing about 30% alfalfa silage and 20% corn silage but the best production with least nitrogen loss to the environment occurred with about 24% alfalfa silage and 26% corn silage (approximately half of the forage from each silage). This also means that dairy farmers can capitalize on the complementary nature of alfalfa and corn silages to reduce the expense of purchasing protein supplements and to reduce nitrogen pollution.
Technical Abstract: Twenty-eight (8 ruminally cannulated) lactating, multiparous Holstein cows were blocked by days in milk and randomly assigned to 7 replicated 4 x 4 Latin squares (28 d periods) to investigate the effects of different dietary ratios of alfalfa silage (AS) to corn silage (CS) on production, N utilization, apparent digestibility, and ruminal metabolism. The 4 diets contained [dry matter (DM) basis]: A) 51% AS, 43% rolled high-moisture shelled corn (HMSC), and 3% solvent soybean mean (SSBM), B) 37% AS, 13% CS, 39% HMSC, and 7% SSBM), C) 24% AS, 27% CS, 35% HMSC, and 12% SSBM), and D) 10% AS, 40% CS, 31% HMSC, and 16% SSBM). Dietary crude protein contents were 17.2, 16.9, 16.6, and 16.2% for diets A, B, C, and D. Intake of DM, yield of milk, 3.5% FCM and fat, milk fat content, and apparent digestibility of NDF and ADF all decreased linearly when CS replaced AS. Effects on fiber digestion and milk fat may have been due to increasing fluctuation in ruminal pH and time pH remained <6.0 when CS replaced AS. Milk protein content increased linearly with increasing CS, but there were no differences in protein yield. There were linear increases in apparent N efficiency, and decreases in N excreted in urine and feces, when CS replaced AS. Production was depressed on diet D. Quadratic analysis indicated milk and protein yields were maximal at dietary AS:CS ratios of, respectively, 37:13 and 31:19. No diet minimized N excretion without negatively affecting production. Diet C, with AS:CS ratio of 24: 27, was the best compromise between improved N efficiency with sustained production. Because it is complementary with AS, it is recommended that CS be fed in AS-based diets to maintain milk yield while improving N utilization.