Estimates of environmental and genetic parameters influencing milk and growth traits of Awassi sheep in Cyprus

Abstract

Data on 1213 ewes and 1382 lambs of both sexes, born between 1978 and 1991 at the Orites Livestock Unit, were used in a study of environmental and genetic factors affecting ewe productivity and lamb growth in the Awassi breed. Genetic and phenotypic parameters were estimated for some production and reproductive traits in ewes and for growth traits in lambs. Year and season of lambing significantly affected all production and reproductive traits in ewes and growth traits in lambs. Lamb birth weight was not affected by season of lambing. Parity (lactation number) had a significant quadratic effect on all ewe and lamb traits except postweaning lamb growth rate, which is probably free from maternal effects. Type of birth and sex were the most important sources of variation in lamb growth with the exception of postweaning daily gain, which was not influenced by type of birth. Estimated heritabilities for ewe production and reproductive characters were modest, but most were high enough to justify selection procedures for their improvement. In particular, the estimates for prolificacy (0.30 ± 0.08) and part (0.58 ± 0.12) or total (0.56 ± 0.11) lactation milk yield indicated that both traits can be improved and particularly prolificacy, which is one of the weaknesses of the breed. The results of the present study indicate that postweaning growth rate is probably the best criterion of selection to improve lamb performance. This criterion, or the 105-day weight, should be superior to weaning weight or preweaning growth rate since they are probably much less influenced by maternal effects that mask the genetic potential of the lamb for fast growth. The absence of genetic antagonisms among ewe or lamb traits indicated that correlated responses in other traits from selection on milk production or postweaning growth would not be negative.