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Title: SEX EFFECTS ON BREED OF SIRE DIFFERENCES FOR BIRTH, WEANING, AND YEARLING WEIGHTS

Author
item Van Vleck, Lloyd
item Cundiff, Larry

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Records at USMARC of progeny of 12 breeds of sire are used as the basis to determine factors to be added to breed association EPD so that EPD of bulls of different breeds can be compared for birth, weaning, and yearling weights and for maternal weaning weight. Calves of both sexes are combined in these analyses. Weights of male and female calves can be considered as separate but correlated traits. Such an analysis resulted in similar estimates of heritability for the two sexes and genetic correlations between genetic expression in males and females of .85 to 1.00. Breeds of sires ranked similarly for male and female weights in general. The greatest exception was for Brahman calves for birth and weaning weights. Breed of sire effects averaged for male and female calves were almost identical to breed of sire effects for the two sexes combined. These results show that considering male and female weights as separate traits is not necessary when calculating across-breed adjustment factors from MARC records. The results also suggest that for combined analysis that the records be adjusted for sex of calf by age of dam effects rather than for separate sex and age of dam effects. This conclusion implies the effect of age of dam is different for male and female calves.

Technical Abstract: Weights of males and females 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 from MARC of progeny of Hereford and Angus dams mated to 12 sire breeds that had been used to calculate breed of sire adjustments in 1996 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 (BWT), weaning (WWT) and yearling (YWT) weights were considered to be 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. Corresponding genetic correlations between expression in males and females were .85, 1.00 and .92. Phenotypic standard deviations were slightly larger and coefficients of variation slightly smaller for males than for females with the 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. 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.