泌乳牛蛋白质利用效率的研究

试验选用日产奶量相近、泌乳60￣100d、平均体重650±10kg、3￣5胎的中国荷斯坦奶牛76头,应用营养模型对日粮蛋白质利用效率进行分析,探讨限制IDCP利用率的因素。结果表明:①日粮RDP的利用效率67.7%;NY/T34-2004与NRC(2001)估测的IDCP分别为2338.1与2505.4.8g/(头·d),差异较大的重要原因是,NY/T34-2004是假定所有原料的RUP的消化系数为0.65。这一假定值不适合选用RUP消化率高的原料配合的高产奶牛日粮;②依据NRC(2001)的营养需要模型,试牛IDCP的需要量为2143.8g/(头·d),而日粮供给的IDCP为2505.4g/(头·d),IDCP利用效率只有85.6%。选用乳蛋白质中EAA含量作参照,利用理想蛋白质理论,进一步对IDCP中EAA与蛋氨酸含量分析显示,两者降低了IDCP利用效率的12.3%。结果提示,对成年泌乳牛,适宜的IDCP中EAA含量应接近乳蛋白质中EAA含量。

Studies on the Efficiency of Utilization of Dietary Protein by Milking Cows

Seventy-six Chinese Holstein cows (with similar daily milk production, 60~100 days after parturition, at an average body weight of 650±10 kg, and at parities 3~5) were used in a feeding trial, where the efficiency of utilization of dietary protein was studied by means of nutrition models. It was shown that the efficiency of utilization of dietary RDP reached 67.7%, indicating that it was an important means for improving dietary protein utilization to reasonably select protein supplements and reduce dietary RDP. The IDCPs estimated by NY/T34-2004 and NRC (2001) were 2338.1 and 2505.4 g/d per cow, respectively, the big difference for which partly resulted from the assumption of the coefficient of RUP digestion at0.65 for all ingredients by NY/T34-2004. Such an estimate was not suitable for high-producing cow rations formulated with RUP highly digestible ingredients. The IDCP requirement for experimental cows was 2143 g/d per cow based upon the NRC (2001) nutritional requirement models. However, the supply of dietary IDCP was 2505.4 g/d per cow, and the efficiency of IDCP utilization was only 85.6%. An analysis of the contents of total EAA and methionine in IDCP showed that they caused a reduction of 12.3% in IDCP utilization.