Effects of corn silage, alfalfa hay, and oat-vetch mixed silage combinations on milk production, rumen fermentation, and nutrient digestibility in high producing dairy cows.

The objective of this study was to explore the effects of corn silage, alfalfa hay, and oat-vetch mixed silage combinations on milk production, rumen fermentation, nutrient digestibility, and feeding cost in dairy cows. Nine multiparous Holstein dairy cows (DIM: 94.11 ± 9 d, milk yield: 41.0 ± 2.5 kg) were each fed 3 experimental diets in a replicated Latin square design. The experimental diets contained corn silage, alfalfa hay, and mixed silage in 3 different forage proportions (diet 1, 40:10:0; diet 2, 30:5:15, and diet 3, 20:0:30; DM basis). Cotton seed meal (CSM) or soybean meal (SBM) were used as the protein source to balance the CP content. The mixed silage was made from oats and vetch grown together in a 50:50 ratio, and all diets were formulated to contain 16% CP and 50:50 forage-to-concentrate ratio (DM basis). Cows fed diet 3 had a 9% reduction in DMI compared with diet 1. Associated with this reduction in DMI, cows fed diet 3 also had reduced yield of milk protein (22.0%), fat (15.7%), and lactose (18.5%) compared with cows fed diet 1. Characteristics of rumen fermentation were similar among diets; however, cows fed diet 3 had lower rumen fluid valerate and higher acetate: propionate ratios compared with diet 1. The N intake was not different among cows fed the 3 diets, but cows fed diet 3 excreted 0.2% less urinary N compared with diet 1. The combinations of corn silage and mixed silage reduced the cost of the diets (diet 1, $0.543; diet 2, $0.503; diet 3, $0.465/kg DM), and whereas milk production was reduced, the feed cost per milk yield was lowest for cows fed diet 3 ($0.404) and highest for cows fed diet 1 ($0.407). We conclude that cows fed diets with combinations of corn silage, alfalfa hay, and mixed silage, consumed less feed and produced less milk but also produced less urinary N and had a lower cost of feed for milk production than cows fed corn silage diets. This demonstrated that partial displacement of expensive corn silage, alfalfa hay, and SBM with mixed silage and CSM reduced costs, but due to the reduced DMI and milk yields, more research on these diets will be needed before they can be recommended as viable options to replace corn silage and SBM diets.