Effects of soybeans roasting and monensin on milk production and composition and milk fatty acids profile of lactating dairy cows

This study was conducted to evaluate the effects of inclusion of roasted whole soybeans seed and monensin in the diets of lactating dairy cows on feed intake, milk production and composition, milk fatty acid profile, efficiency of nitrogen (N) and net energy (NEL) utilization for milk production and nutrient digestibility. Four multiparous Holstein lactating dairy cows (third parity; 656±55 kg of live weight; 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 was a total mixed ration (TMR) consisting of 40% forage and 60% concentrate mixture on dry matter (DM) basis. These cows were randomly assigned to one of the four dietary treatments as their main source of fatty acids (FA). The first treatment was the control diet (C) of unprocessed whole soybeans seed, second was control diet supplemented with 24 mg of monensin/kg of DM (M), the third was roasted whole soybeans seed (R) and the fourth treatment was R diet supplemented with 24 mg of monensin/kg of DM (RM). Dietary supplementation with whole roasted soybeans seed or monensin had no effect on milk production, milk fat, protein and lactose concentrations, utilization efficiency of N and NEL, and DM and nutrient intake (P>0.05). The digestibility of organic matter (OM), ether extract (EE) and neutral detergent fiber (NDF) were not affected by the dietary treatments (P>0.05). The digestibility of DM and crude protein (CP) tended to be lower in cows fed with the RM diet compared with cows fed the other diets (P=0.08 and 0.06, respectively). Orthogonal contrasts showed that the digestibility of DM and CP was lower in roasted soybean-fed cows than raw soybean-fed cows (P<0.05). While feeding the R diet decreased milk fat concentration of 6:0 (P<0.05), the milk fat concentration of c9, t11 conjugated linoleic acid (CLA) tended to be increased (P=0.08). Dietary treatments had no effect on milk fat concentrations of saturated, unsaturated, short chain, medium chain and long chain FA (P>0.05). Although inclusion of roasted whole soybeans seed in the diet tended to elevate the milk fat concentration of c9 and t11-CLA, it also lowered the digestibility of DM and CP so the overall milk production was not improved.