|Brito, A - UW-MADISON|
Submitted to: International Silage Conference
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2005
Publication Date: July 4, 2005
Citation: Broderick, G.A., Brito, A.F. 2005. Effects of varying dietary ratios of lucerne to maize silage on production and microbial protein synthesis in lactating dairy cows. Proceedings of XIVth International Silage Conference. p. 172. Technical Abstract: Lucerne silage (LS) is high in total CP and rumen-degraded protein (RDP) but low in fermentable energy while maize silage (MS) is a good source of fermentable energy but low in RDP. Thus, these silages are complementary and feeding them at optimum ratio should increase nutrient efficiency in lactating cows. The objective of this experiment was to optimise the dietary LS:MS ratio for production, microbial protein and N utilisation. Twenty-eight (8 with rumen cannulae) multiparous Holstein cows were blocked by days-in-milk and assigned to replicated 4 x 4 Latin squares (28 d periods). The 4 diets were: A [51% LS, 43% high-moisture shelled maize (HMSM), and 3% solvent soyabean meal (SSBM)], B (37% LS, 13% MS, 39% HMSM, and 7% SSBM), C (24% LS, 27% MS, 35% HMSM, and 12% SSBM), and D (10% LS, 40% MS, 31% HMSM, and 16% SSBM). Dietary CP was 17.2, 16.9, 16.6, and 16.3%, respectively. Intake and yield of milk and milk components were determined during the last 14-d of each period. Rumen digestion and metabolism, including microbial protein yields, were quantified using omasal sampling. Dry matter intake, yield of milk and fat, and milk fat content decreased linearly when MS replaced LS. Depressed fat yield may have resulted from lower rumen acetate. Milk protein content increased linearly with increasing MS; however, there was a quadratic effect of LS:MS on protein yield with maximum at 31% dietary LS. Nitrogen efficiency increased because N excreted in urine and feces decreased linearly when MS replaced LS. Production was significantly depressed on LS:MS of 10:40 and microbial NAN flow was lowest on this diet. A quadratic effect also was observed on microbial protein synthesis with maximum at 38% LS, suggesting that maximal microbial protein formation required a balance between fermentable energy and RDP supply. The results of this study diets indicate that maximal milk protein yield and microbial protein supply occurred at dietary LS:MS ratios of 31:19 to 38:12.