Within-Cow Regression of Milk-Energy Yield on Age and Liveweight

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Abstract
The independent influence of age and live weight on milk-energy yield is derived by the adjustment of an equation by least squares, within cow. Two within-cow equations are FCM =[long dash]1.69 + (0.0413 [plus or minus] 0.0045) W + (0.001 [plus or minus] 0.022) A and 1000 FCM/W = 38.30 + (0.0012 [plus or minus] 0.0032) W + (0.004 [plus or minus] 0.016) A. FCM is daily milk-energy yield in pounds of 4% milk for the 243-day partial lactation; W is live wt. in pounds within 31 days after calving for the same lactation; A is conceptual age at calving in months. It is concluded that the correction of milk yield for age is biologically unsound because age has no significant effect on yield, independent of live wt.