Soybean silage in dairy heifers' diets: ruminal fermentation, intake and digestibility of nutrients

This study was designed to determine the effects of soybean silage (SS) in diets of dairy heifers on nutrient intake and digestibility, feeding behaviours, rumen fermentation, N utilisation, and microbial N synthesis. Twelve Jersey heifers (307 +/- 3 kg body weight and 15 +/- 3.2 months of age) were assigned to a 4 x 4 Latin square design experiment with 21 d-periods, 14 d for adaptation and 7 d for sampling. Treatments were: 1) control (0), diet without SS and containing 750 g/kg DM corn silage (CS); 2) 250: diet with 250 g/kg DM SS and 500 g/kg DM CS; 3) 500: diet with 500 g/kg DM SS and 250 g/kg DM CS; and 4) 750: diet with 750 g/kg DM SS and without CS. The level of SS quadratically affected DM, crude protein, and neutral detergent fibre intake and digestibility. Soybean silage decreased linearly ruminal acetate concentration and quadratically affected the ruminal concentration of propionate and total volatile fatty acids. A linear increase was observed for microbial N synthesis as the dietary level of SS increased. Soybean silage may be used at levels between 325 and 395 g/kg DM, instead of CS to maximise DM intake and digestibility.