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Effects of Environment on Phenotypic and Genetic Variation in Sheep

University of California, Davis

Abstract

Five years' data on an experiment conducted at two locations using whiteface Targhee-type sheep have been used to study genotype-environment interaction and the effects of environment on phenotypic and genetic variation. The traits studied include birth and 120-day weights, gain from weaning to fall and from fall to shearing, 450-day weight, grease fleece weight, staple length, fleece grade, conformation score and face score.

The results indicate that for most traits, including the trait under selection (120-day weight), the phenotypic variance is higher in the "good" than the "poor" environment, with the result that the selection differentials are also higher for the former. The higher variance is not explained by higher means, since it was found for traits for which the means did not differ. Even though the average paternal half-sib heritability estimates for both 120-day weight and yearling traits are higher in the better environment, the realized heritability estimates for 120-day weight from the response to 3 years of selection are not.

There was no evidence of large genotype-environment interactions.

Estimates of genetic correlations indicate that the only characters likely to be affected by selection for 120-day weight are 450-day weight and conformation score. Both will be affected favorably. No important genetic correlations were found between 120-day weight and fleece traits.

¹ Present address: Faculty of Veterinary Science, P.O. Box 32, Khartoum North, Sudan.

² Department of Animal Husbandry.

³ The authors acknowledge the assistance of D. T. Torell and G. M. Spurlock. The assistance of the Davis Computer Center, partially supported by NIH grant FR-00009, is also acknowledged.