Effect of Frequency and Spacing of Sampling on Accuracy and Precision of Estimating Total Lactation Milk Yield and Characteristics of the Lactation Curve

Dally milk weights of 255 cows in seven herds were sampled using different frequencies and spacings of samples to investigate accuracy and precision of estimating total yield. There were four sampiing methods with equal intervals and six methods with unequal intervals. Unequally-spaced samples were placed according to varying degrees of relative emphasis on peak production period of a lactation, which was defined as 15 to 90 d postpartum. For each sampling method, total lactation yield was estimated by linear interpolation and by fitting a nonlinear function to the lactation curve. Fixed factors affecting biases in estimators of total yield and of parameters of the lactation curve were analyzed by a multivariate linear model.