Effect of soybean roasting and monensin on microbial protein synthesis, ruminal parameters and plasma metabolites of lactating dairy cows

Abstract

This study was conducted to evaluate the effects of inclusion of roasted whole soybean seed and monensin (MO) in the diets of lactating dairy cows on plasma metabolites, ruminal parameters, and microbial protein synthesised in the rumen. Four multiparous Holstein lactating dairy cows (third parity; 656 ± 55 kg of liveweight; 83 ± 10 days in milk; 35 ± 4 kg/day milk yield) were assigned to a balanced 4 × 4 Latin square design. Each experimental period lasted 21 days with 14 days of treatment adaptation and 7 days of data collection. The control diet (C) was a total mixed ration consisting of 40% forage and 60% concentrate mixture on a dry matter (DM) basis. These cows were randomly assigned to one of the four dietary treatments. The first treatment was the C diet of unprocessed whole soybean seed, second was the C diet supplemented with 24 mg of MO/kg of DM (M), the third was roasted whole soybean seed (R) and the fourth treatment was R diet supplemented with 24 mg of MO/kg of DM (RM). Urinary excretion of creatinine and purine derivatives, microbial protein synthesised in the rumen, rumen pH and rumen concentrations of volatile fatty acids and ammonia were similar among the dietary treatments (P > 0.05). Orthogonal contrasts showed that the rumen concentration of acetate was lower in MO-supplemented cows than non-supplemented cows (P < 0.05). Dietary treatments had no effects on plasma concentrations of glucose, total cholesterol, triglycerides and total protein (P > 0.05). Plasma concentration of urea was significantly lower in cows fed with the RM diet compared with cows fed the C and M diets (P < 0.05). In conclusion, dietary treatments had no effect on microbial protein synthesised in the rumen, plasma metabolites (except for plasma concentration of urea) and ruminal parameters of dairy cows.