Standard deviations of differences between estimated and actual yields are shown in Table 3. The standard deviations of differences between either BP method and both measures of actual yield were smaller than for differences between TIM and actual yield for all testing environments. For comparisons of estimated yield with 305-d actual yield, standard deviations of differences for both BP methods were 4%smaller than for TIM for MN testing, 6% smaller for AP testing, and 10% smaller for TRI testing, which indicates that both BP methods have a mod rate advantage over TIM despite correlations between TIM and BP estimates of nearly 1.0. The advantage increased for testing environments in which weights and samples were recorded at less optimal intervals and frequencies. The main advantage of a BP method over TIM is that lactation records are regressed toward a population mean when few weights or samples are available. A regressed TIM might rival a BP method. However, TIM cannot be used to predict missing values for correlated traits, and a method to regress the lactation yield is not obvious, particularly when the testing intervals are not equally spaced throughout the lactation. The opportunity to increase the accuracy of predicting 305-d yield by 4 to 10% is important and could result in large economic returns in the efficiency of milk yield. Often, culling decisions are based on a cow’s actual yield, real producing ability, or predicted producing ability (13). Because the repeat abilities of milk and component yields are near 50%, greater accuracy in calculating those rankings for early parities would mean that cows selected for survival by herd managers would yield more during later lactations than if the rankings had been based on less accurate TIM estimates
Comparison of Test Interval and Best Prediction Methods for Estimation of Lactation Yield from Monthly, a.m.–p.m., and Trimonthly Testing (PDF Download Available). Available from: https://www.researchgate.net/publication/13221765_Comparison_of_Test_Interval_and_Best_Prediction_Methods_for_Estimation_of_Lactation_Yield_from_Monthly_am-pm_and_Trimonthly_Testing [accessed May 8, 2016].