Tyrrell H F, Brown A C, Reynolds P J, Haaland G L, Bauman D E, Peel C J, Steinhour W D
Ruminant Nutrition Laboratory, U.S. Department of Agriculture, Beltsville, MD 20705.
J Nutr. 1988 Aug;118(8):1024-30. doi: 10.1093/jn/118.8.1024.
Effects of exogenous bovine somatotropin (bST) on energy and nitrogen utilization by high producing dairy cows were examined. Nine cows received bST (51.5 IU/d) or exipient (control) in a single reversal design involving 14-d treatment periods. Energy and nitrogen balances were measured in open-circuit respiration chambers. Yield of 4% solids-corrected milk was increased by 22% with bST treatment. Dry matter intake and the apparent digestibilities of dry matter, energy and nitrogen were not altered by treatment. The only significant component of nitrogen utilization that was altered by bST treatment was an increase in milk nitrogen secretion. Cows were in negative tissue nitrogen balance during the control period (-21 g/d) and tended to become more negative during the bST treatment period (-34 g/d). Heat energy loss and milk energy secretion were increased with bST treatment. Tissue energy balance was -1.1 Mcal/d during the control treatment period and the use of energy reserves with bST treatment decreased tissue energy balance to -9.8 Mcal/d. Changes in heat production with bST treatment were equal to those predicted from the changes in milk and body tissue. Overall, the results demonstrated that bST treatment increased yield of milk and milk components even when cows were in negative nitrogen and energy balance. Effects of bST were predominantly associated with nutrient partitioning, and observed heat loss (associated with maintenance and partial efficiencies of milk synthesis and tissue utilization) did not differ from predicted heat loss.
研究了外源性牛生长激素（bST）对高产奶牛能量和氮利用的影响。9头奶牛采用单反转设计，接受bST（51.5 IU/天）或赋形剂（对照），每个处理期为14天。在开路呼吸室中测量能量和氮平衡。bST处理使4%固体校正乳产量提高了22%。处理对干物质摄入量以及干物质、能量和氮的表观消化率没有影响。bST处理改变的唯一显著的氮利用成分是乳氮分泌增加。在对照期，奶牛处于负组织氮平衡状态（-21克/天），在bST处理期趋于更负（-34克/天）。bST处理使热能损失和乳能量分泌增加。对照处理期组织能量平衡为-1.1兆卡/天，bST处理时能量储备的利用使组织能量平衡降至-9.8兆卡/天。bST处理引起的产热变化与根据乳汁和身体组织变化预测的结果相当。总体而言，结果表明，即使奶牛处于负氮和能量平衡状态，bST处理仍能提高牛奶和乳成分的产量。bST的作用主要与营养分配有关，观察到的热损失（与维持以及乳汁合成和组织利用的部分效率有关）与预测的热损失没有差异。
