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Correlation between Purebred and Crossbred Half-Sibs in Sheep

Iowa State University, Ames

Abstract

The main purpose of this investigation was to evaluate rams by means of both purebred and crossbred progeny performance and to study the relationship between the two evaluations. The character studied was weaning weight.

Data were available on 1,006 lambs collected during the period from 1958 through 1962 from the U.S.D.A. sheep flock of the Agricultural Research Center, Beltsville, Maryland. Breeds involved were Hampshire, Shropshire, Southdown and Merino. There were 452 and 554 purebred and crossbred progeny, respectively, from these sires.

The model used included breed of sire, sire within breed, sex, type of birth, age of dam, band and the regression of weight on age at weaning. Analyses were carried out within years separately on purebreds and crossbreds and pooled across years.

From the pooled analysis ²_s was estimated as 1.16 and .57 in the purebreds and crossbreds, respectively. The covariance between sire performance in the purebreds and crossbreds was calculated as .67. Thus, the correlation coefficient was estimated to be .82.

Heritability estimates calculated from purebreds and crossbreds were .26±.14 and .12±.10, respectively.

Heritability estimates and the correlation above were used to calculate the ratio of indirect response in the crossbred progeny when selection was based on the performance of the purebreds to direct response. The ratio was 1.12 on the basis of progeny testing with 10 progeny per sire in each purebred and crossbred group. The assumption was made that selection intensities are equal in both cases.

In general, the investigation indicated that selection on the performance of the purebred progeny will also improve crossbred offspring.

¹ Present address: Department of Animal Production, College of Agriculture, University of Ain-Shams, Shubra AIKhaima, Cairo, Egypt, U.A.R.

² Present address: Sheep and Fur Animal Research Branch, A.H.R.D., U.S.D.A., Beltsville. Maryland 20705.