Growth Performance of Crossbred Lambs and Productivity of Kurdi Ewes as Affected by the Sire Breed under Extensive Production System

Crossbreeding of four Iranian fat-tailed sheep breeds, namely Kurdi (K), Chaal (C), Afshari (A) and Sanjabi (S) was carried out to determine the ram breed effects on productivity of Kurdi fat-tailed ewes (K) under extensive production system. A total of 475 Kurdi ewes were mated to 24 rams from the above four breeds resulting in 454 lambs. Ram breed had a significant influence on early growth traits of the lambs. Lambs sired by C rams were heavier than the other lambs (P< 0.05) at birth and weaning. Body weight at 160 days of age (W160) in crossbred lambs was significantly higher than that of the purebred lambs while crossbred lambs for W160 were similar (P> 0.05).Greasy fleece weight of lambs at first shearing (GFW) and fat-tail measurements were significantly affected by ram breed. Number of lambs born and number of lambs weaned per ewe lambed or per ewe joined were similar among the four groups, whereas there was significant effect on productivity. In general, ewes mated to Chaal ram had higher productivity than those mated to other ram breeds.