Effects of high ambient temperature and restricted feed intake on nitrogen utilization for milk production in lactating Holstein cows.

摘要

Effects of high ambient temp. and feed restriction on N utilization for milk production in lactating cattle were investigated in a series of 3 experiments. In the 1st experiment, N utilization in 4 cattle fed ad libitum in a 2 x 2 crossover design under constant moderate (18°C) or high (28°C) ambient temp. was investigated. Milk N secretion and protein concn. were found to decrease under high ambient temp. (P < 0.01 and P < 0.05, respectively). The 2nd experiment investigated N utilization in 4 cattle under constant moderate ambient temp. in a 2 x 2 crossover design with ad libitum or 70% ad libitum feed intake. Both milk N secretion and protein concn. decreased with feed restriction (P < 0.05). The 3rd experiment investigated N utilization in 4 cattle fed 70% ad libitum in a 2 x 2 crossover design under constant moderate or high ambient temp. Milk protein concn. decreased under high ambient temp. (P < 0.01). A tendency for reduced milk N secretion under high ambient temp. was also observed (P < 0.10). It is suggested that reduced N utilization for milk production at high ambient temp. is mainly caused by reduced feed intake and the high ambient temp. itself.