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Title: DIFFERENCES IN BREED OF SIRE DIFFERENCES FOR WEIGHTS OF MALE AND FEMALE CALVES

Author
item VAN VLECK, LLOYD
item CUNDIFF, LARRY

Submitted to: Beef Improvement Federation Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/4/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Differences between breeds of sire in weights of calves may be different for bull and heifer calves. A second question is whether expression of a sire's genotype will be the same in bull and heifer calves. A third question is whether heritability is the same for bull and heifer calves. Records from USMARC of calves of bulls of 12 breeds out of Hereford and Angus dams were used to address these questions. In general, differences due to breeds of sire were similar for bull and heifer calves for birth, weaning, and yearling weights. A major exception was that Brahman sired bull calves were much larger relative to bull calves of other sire breeds as compared to the differences for heifer calves. Adjustment factors to use to convert within-breed EPD to across-breed EPD averaged equally over both sexes were almost identical to adjustment factors computed from sex- adjusted records. The conclusion is that bull and heifer weights do not need to be considered to be separate traits for the calculation of across- breed adjustment factors. Calculation of across-breed adjustment factors, however, should not be done unless calves of both sexes are included in the calculation.

Technical Abstract: Weights of male and female calves can be considered to be correlated traits with different averages and variances. This study attempted to determine if defining traits as expressed in males or in females would change estimates of breed of sire differences needed to calculate across-breed factors for adjustment of within-breed EPD to across-breed EPD. Records of progeny of Hereford and Angus dams mated to 12 sire breeds previously used to calculate breed of sire adjustments were used. Breeds of sire were HEreford, Angus, Shorthorn, Brahman, Simmental, Limousin, Charolais, Maine- Anjou, Gelbvieh, Pinzgauer, Tarentaise, and Salers. Female and male records for birth, weaning and yearling weights were considered separate although correlated traits. Heritability estimates for expression as females and males were: .44 and .47 for BWT, .25 and .19 for WWT, and .55 and .49 for YWT with genetic correlations between sexes of .85, 1.00 and .92. Phenotypic standard deviations were slightly larger and coefficients of variation slightly smaller for males than for females with largest differences for YWT. Breeds ranked similarly for female and male weights with major exceptions being Brahman for BWT and WWT; Simmental for WWT and YWT; Tarentaise for BWT; Hereford for WWT, and Limousin, Maine-Anjou and Gelbvieh for YWT. Averages of breed of sire contrasts for expression in females and males were almost identical to contrasts from analyses of combined male and female records. Largest differences between averaged and combined breed of sire contrasts were about 2 lb for BWT and WWT and about 4 lb for YWT. The conclusion is that considering male and female weights as separate traits is not needed in calculation of across-breed adjustment factors from MARC records.