Abstract
The adjusted 205-day weaning weights of 13,937 Hereford and Angus calves recorded in the Oklahoma Beef Cattle Improvement Program from 1959 through 1962 were used in this study. Each calf was classified according to age of dam, sex, breed, type of pasture, area of the state, month of birth and type of management. The data were analyzed by least squares to investigate the main effects of these seven factors. To investigate two-way interactions least-squares analyses were computed within each sex, breed, type of pasture, season of birth and type of management. The importance of interactions was examined by comparing least-squares constants computed for a given level of one factor within different levels of another factor. The criterion for assessing the significance of interaction was whether or not 95% confidence intervals for the least-squares constants overlapped. The results of the analysis of main effects indicated that age of dam, sex, area, month of birth and type of management had significant (P<.01) and important influences on weaning weight, each accounting for more than 5% of the total variance. The least-squares estimates for age of dam indicated that weaning weight increased 22 kg. as cows increased in age from 2 to 4 years, suggesting that classifying cows into 3- to 5-month increments between 2 and 4 years of age would result in more accurate corrections than those that result from yearly increments. The results of interaction analyses indicated that the effect of age of dam was essentially the same regardless of sex, breed, type of pasture, season of birth or type of management. Sex by type of management, month of birth by type of pasture and month of birth by type of management appear important enough to be taken into account in adjusting weaning weights. Copyright © 1966. American Society of Animal Science. Copyright 1966 by American Society of Animal Science