In Vitro Rumen Fermentation Characteristics, Estimated Utilizable Crude Protein and Metabolizable Energy Values of Grass Silages, Concentrate Feeds and Their Mixtures

SIMPLE SUMMARY: We report the in vitro rumen fermentation characteristics, utilizable crude protein, and energy values of four different formulations of concentrate feeds, three contrasting qualities of grass silages, and mixtures thereof (45% concentrate, 55% silage, dry weight basis) using the ANKOM RF wireless gas production system. The concentrates were two pelleted diets (control concentrate for dairy cows and alkaline concentrate with ammoniated barley) and two mash forms (concentrate with ingredients of the alkaline diet prior to alkalization and concentrate with basal ingredients as in the alkaline diet with feed-grade urea). The grass silages were early cut, late cut, and a 1:1 mix thereof. For mixed diets, no interaction effects of the concentrate feeds by silage quality were observed for the tested parameters. For concentrates, the pelleted diets were higher in in vitro dry matter digestibility and molar proportion of propionate. The alkaline pelleted concentrate produced a higher utilizable crude protein value than others. For silages, estimated protein and energy values, total short-chain fatty acids, and molar proportions of propionate and branched-chain fatty acids decreased with increasing stage of maturity. Results for silages and their mixtures with concentrates highlight the importance of silage quality in dietary energy and protein supply for ruminants. ABSTRACT: Four formulations of concentrate feeds, three contrasting qualities of grass silages, and mixtures of the silages (55%) and concentrates (45%, dry weight) were tested for in vitro fermentation kinetics, in vitro dry matter degradation (IVDMD), utilizable crude protein (uCP), and metabolizable energy (ME) values. The concentrates were pelleted control concentrate for dairy cows (CONT-P); pelleted alkaline concentrate with ammoniated cereal grains (ALKA-P); mash form concentrate with ALKA-P main ingredients but with feed-grade urea and barley replacing ammoniated cereal grain (UREA-M); and mash form of ALKA-P ingredients prior to alkalization (ALKA-M). The grass silages were early cut, late cut, and a mixture (1:1) of early and late cut. The objectives were to test if the feeds differed in the tested parameters within each feed category and assess the modulatory effect of concentrate feeds on the grass silage fermentation characteristics in the mixed diets. No interaction effects of the concentrate feeds by silage quality were observed for the tested parameters in the mixed diets. For concentrates, the pelleted diets were higher (p < 0.05) in IVDMD and molar proportion of propionate but lower in butyrate. The ALKA-P produced the highest estimated uCP (p < 0.01). For silages, uCP, ME, total short-chain fatty acids (VFAs), and molar proportions of propionate and branched-chain VFAs decreased (p < 0.05) with increasing stage of maturity. In conclusion, the ALKA-P could match the CONT-P in uCP and ME values and fermentation characteristics. Results for silages and their mixtures with concentrates highlight the importance of silage quality in dietary energy and protein supply for ruminants.