RAPESEED MEAL VERSUS SOYBEAN MEAL AS THE ONLY PROTEIN SUPPLEMENT FOR LACTATING COWS FED CORN SILAGE ROUGHAGE RATIONS

Digestion, nitrogen balance, and a 112-day lactation trial were conducted with Holstein–Friesian cows fed corn silage as the only roughage, and concentrate rations containing either rapeseed meal (RSM) or soybean meal (SBM) as the only source of supplemental protein. The RSM and SBM consumed in the lactation trial represented 11.8 and 10.6% of the total daily dry matter intake, respectively. Digestibility of total ration crude protein was lower (P < 0.05) for RSM- than SBM-supplemented cows; nitrogen retention and efficiency of nitrogen utilization, however, was comparable for cows in the two treatment groups. Daily milk production, 4% fat-corrected milk production, percent milk fat, protein, and nonfat solids were greater (P < 0.05) for cows fed concentrate containing SBM than for those fed RSM as the source of supplemental protein. Milk production declined more for cows fed RSM compared with those fed SBM during the 112-day trial.