Statistical Methods for Improving Sensitivity in Dairy Cattle Feeding Experiments

This study compares four methods of statistically analyzing performance data from a dairy cattle feeding experinmnt. The basic design (modified switch-back) involved a pre-experimental (Period I), an experimental (Period II), and a postexperimental (Period III) period. Periods I and III were standardization, or control periods, during which all cows were fed the same. Thirty-sLx Holsteins were used to determine the effect of six treatments (2 X 3 factorial) on milk and solids-corrected milk yield, milk fat and solids-not-fat percentage, dry matter and estimated net energy intake, and estimated net energy/solidscorrected milk. The four methods of analysis ntilized different data as follows: (A) average performance in Period II, (B) average performance in Period II adjusted by covariance for average performance in Period I, (C) average performance in Period II adjusted by covariance for both average performance in Period I and body weight at the end of Period I and (D) difference in average performance in Period II relative to that in Periods I and III.