Predicting 365-day hip height in performance tested bulls

A total of 226 bulls, with pre-test, initial, on-test and final variables recorded, were used to derive stepwise regression equations for predicting 365-day hip height.

The first prediction equation, using pre-test and initial variables, contained breed, initial hip height, initial age, month of birth, weight per day of age to weaning and initial weight, which entered the equation in that order. The coefficient of determination was .80. The second equation, using on-test variables, contained the variables pre-weaning management, final hip height, initial age, average daily gain on test, initial hip height and month of birth, which entered in that order. These accounted for 92 percent of the variation in 365-day hip height. The third equation, using all variables, contained the same variables as the second equation. The only difference was its entry of the variable number of days from weaning to start of test, in the final step, and this equation accounted for 93 percent of the variation in 365-day hip height. An analysis of variance was performed on each of these equations to determine which variables should be included in the equations. In the third equation, number of days from weaning to start of test was not significant, so the second and third equations were the same. Including pre-test variables did not increase the effectiveness of the on-test equation in predicting 365-day hip height.

Values for 365-day hip height predicted by the two regression equations and the two algebraic equations, one recommended by the Beef Improvement Federation, were compared to actual 365-day hip height values. Means, variances and minimum and maximum values were compared. An analysis of variance was performed with the predicted and actual 365-day hip height values as the dependent variable and the type of equation as the independent discrete variable. The algebraic equation was found to be significantly different from the actual value and other prediction equation values. These analyses indicated that the pre-test and initial regression equation can satisfactorily predict 365-day hip height and should be used if an earlier prediction is desired, although it does not predict extreme values as well as those close to the mean. The on-test regression equation was the most accurate predictor of 365-day hip height but required the most data and was not as easily calculated. The equation recommended by the Beef Improvement Federation was the easiest to calculate but had a tendency to over predict 365-day hip height.

Results of the analysis of variance of average daily gain on test showed age of dam, month of birth, breed, change in hip height on test and initial age all to have significant effects.