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Phenotypic Relationships within Angus and Hereford Females. II. Repeatabilities of Progeny Weaning Weights¹

Oklahoma State University, Stillwater 74074

Abstract

Weaning weights (WW) and their herd-year ratios (WWR) of 2,664 Angus calves of 680 cows and 634 Hereford calves of 183 cows were used to determine if calves raised in consecutive years were more alike than more distantly separated maternal half-sibs. Intraclass (cow) correlation WW and WWR repeatabilities of .27 ± .02 and .27 ± .02 for Angus and .50 ± .04 and .50 ± .04 for Herefords, respectively, were different between breeds (P<.01). As years of rearing of maternal half-sib pairs became farther apart (1 to 8 years), linear regression WW repeatabilities of each later on each earlier record of the same cow pooled across herds and within years of separation of record pair subclasses decreased from .29 ± .02 to .14 ± .10 for Angus and from .53 ± .04 to .12 ± .30 for Herefords. Within breed, no differences approaching significance were found between repeatabilities of WW and WWR. Pooled regressions of both traits for maternal half-sib pairs reared each of 1 through 6 and 1 through 5 years apart for Angus and Herefords, respectively, were significant (P<.05) and for those 1, 2, 3 and 4 years apart were different between breeds (P<.05). Pooled regressions for progeny records 5 and 4 years or less apart for Angus and Herefords, respectively, were of approximately the same magnitudes as the corresponding intraclass correlation of each trait. These results indicate that progeny WW's and WWR's are both good indicators of a cow's subsequent productivity through 5 years, particularly in the case of Herefords; but both have limited predictive value for cow productivity beyond that time.

¹ Journal article 2817 of the Agricultural Experiment Station, Oklahoma State University, Stillwater. This research was conducted in cooperation with the U.S.D.A. Agricultural Research Service, Southern Region.

² Present address: Department of Animal Science, Louisiana State University, Baton Rouge 70803.