Response from selection in a herd of Brahman and Hereford cattle

Abstract

Responses from selection in a Brahman herd and a Hereford herd at the Livestock and Forage Research Center at McGregor, Texas, were estimated from data collected since 1950. Records on 390 Brahman and 1450 Herefords were included in analyses to obtain least-squares constants for fixed sources of variation. Birth weight, weaning weight, average daily gain and weight per day of age records were adjusted for environmental effects by use of the constants. Means and standard deviations were computed from the adjusted data for each sex and pooled to obtain overall estimates. Records of Brahman and records of Herefords eligible for registration were most suited for this study. The two groups of data were analyzed separately but in a similar manner. Annual means were regressed on time expressed in years to obtain an estimate of average phenotypic change per year. Repeated matings from all breeds and crosses raised at the Research Center were used to estimate yearly environmental trends. The environmental difference between any two consecutive years was taken as the average of the differences between adjusted weights of calves produced by consecutive repeated matings. The regressions of means of differences in consecutive time periods yielded estimates of environmental trends. ...