Changes in the metabolic profile and performance of dairy cows fed two dietary crude protein concentrations

According to a 2 × 2 cross-over design, 14 lactating Holstein–Friesian cows were fed two isofibrous and isoenergetic diets based on either 14.5 % of crude protein (LOW CP diet) or 16.5 % (HIGH CP diet). Milk yield and quality and metabolic profile were detected during the third week of each experimental period. Dietary treatment had no effect on dry matter (DM) intake (21.0 kg/d on average), milk yield (34.7 kg/d on average), and milk protein content (3.48 % on average). LOW CP fed cows showed a lower milk urea content (19.4 vs. 29.7 mg/dl; P< 0.01). In LOW CP treatment, it was observed a significant increase of plasma globulins, glucose, and creatinine meanwhile the urea level was significant lower. The efficiency of CP utilization was higher (0.39 vs. 0.34; P<0.05) for the LOW CP group.