MacNeil M D, Mott T B
Fort Keogh Livestock and Range Research Laboratory, ARS, USDA, Miles City, MT 59301, USA.
J Anim Sci. 2000 Sep;78(9):2299-304. doi: 10.2527/2000.7892299x.
The maintenance energy required to sustain the cow herd is a major cost of beef production. This work proposes modifying parameter estimates for a population-specific lactation curve with genetic evaluations for the maternal genetic effect on calf gain from birth to weaning to provide inputs for a commonly used prediction of energy requirement. Daily milk production (y) was modeled as a function of stage of lactation (T, d) using the function y = AT(B)exp(-CT) modified to incorporate effects of genetic evaluation for the maternal effect on calf gain from birth to weaning and age of dam. A 1-kg increase in predicted maternal breeding value for calf gain from birth to weaning from within-herd genetic evaluation increased the lactation curve parameter A by 10.3+/-4.6% and reduced the B parameter by 1.0+/-0.6%. Similarly, a 1-kg increase in maternal breeding value for gain from birth to weaning from national cattle evaluation increased the A parameter by 1.7+/-0.2%. Corresponding estimates of peak milk yield and time of peak lactation were derived for individual animals from their genetic evaluation. Additional inputs for predicting maintenance energy requirements were derived from genetic evaluations for birth weight and mature size. The methodology is demonstrated using genetic evaluations of sires from the Miles City Line 1 Hereford population. Further refinement and application of this methodology may facilitate characterization of beef cattle seedstock for their potential genetic contributions to profitability.
维持牛群所需的维持能量是牛肉生产的一项主要成本。这项工作提出，利用对母牛从出生到断奶期间对犊牛增重的母系遗传效应的遗传评估，修改特定群体泌乳曲线的参数估计值，以为常用的能量需求预测提供输入。每日产奶量（y）被建模为泌乳阶段（T，天）的函数，使用的函数为y = AT(B)exp(-CT)，并进行了修改，以纳入对母牛从出生到断奶期间对犊牛增重的母系效应和母牛年龄的遗传评估影响。在牛群内部遗传评估中，从出生到断奶期间犊牛增重的预测母系育种值每增加1千克，泌乳曲线参数A增加10.3±4.6%，参数B降低1.0±0.6%。同样，在全国牛群评估中，从出生到断奶期间增重的母系育种值每增加1千克，参数A增加1.7±0.2%。从个体动物的遗传评估中得出了峰值产奶量和泌乳高峰期时间的相应估计值。预测维持能量需求的其他输入值来自对出生体重和成熟体型的遗传评估。使用米尔斯城1号赫里福德牛群种公牛的遗传评估展示了该方法。该方法的进一步完善和应用可能有助于表征肉牛种畜对盈利能力的潜在遗传贡献。
