Abstract
This study was conducted to estimate genetic parameters and trends for reproduction traits using data collected at the breeding station of Iran-Black sheep during 1980 to 2004. The traits included in the analyses were litter size at birth (LSB) and weaning (LSW) and litter mean weight per lamb born (LMWLB) and weaned (LMWLW) as basic traits, and total litter weight at birth (TLWB) and weaning (TLWW) as composite traits. Direct heritability estimates for LSB, TLWB, LMWLB, LSW, TLWW and LMWLW were 0.11, 0.07, 0.33, 0.08, 0.09 and 0.11, respectively. The permanent environmental effects had significant impact on all traits and ranged from 0.05 to 0.16. Effect of service sire was highly significant (p < 0.01) for all traits except LMWLW. Estimates of genetic correlations ranged from -0.76 (LSB-LMWLB) to 0.98 (LSB-LSW). Phenotypic and environmental correlations were generally lower than those of genetic correlations. Environmental correlations ranged from -0.55 (LSW-LMWLW) to 0.99 (LSB-LSW). Also, the estimated correlation for the effect of service sire ranged from -0.77 (LMWLB-TLWW) to 0.96 (LSB-LSW and LSB-TLWW). The results suggest that selection based on TLWB could be more effective than the other traits to enhance reproductive performance in Iran-Black ewes.
Highlights
There are many native sheep breeds in Iran (27 breeds)
Traits considered as basic were litter size at birth (LSB, the number of lambs born alive per ewe lambing within a year (1, 2 or 3)), litter size at weaning (LSW, the number of lambs weaned per ewe lambing within a year (0, 1 or 2)), litter mean weight per lamb born (LMWLB) and litter mean weight per lamb weaned (LMWLW).Composite traits were total litter weight at birth per ewe lambing (TLWB, refers to the sum of the birth weights of all lambs born per ewe lambed) and total litter weight at weaning per ewe lambing (TLWW, refers to the sum of the weights of all lambs weaned per ewe lambed)
The estimated service sire correlation for LSB, LSW and LMWLB and LMWLB and TLWW in the present study indicates that undesirable service sire effects have a tendency to reduce numbers of lambs born and weaned
Summary
There are many native sheep breeds in Iran (27 breeds). Iranian native sheep are composed mainly of fat tailed, carpet-wool breeds unique to different regions (Farid, Makarechian, & Sefidbakht, 1977). Iran-Black sheep, originating from a crossing of Balouchi ewes with Chios rams, is a composite breed developed in 1975 at the Abbasabad sheep breeding station located in northeast of Mashhad, RazaviKhorasan province. This new breed is well adapted to harsh conditions (Rashidi, 2013). The most important component of the overall productivity of sheep is ewe productivity efficiency In such case, improving the number of lambs weaned and weight of lambs weaned per ewe per year has been proposed to be the most economically important (Duguma, Schoeman, Cloete, & Jordaan, 2002; Olivier, Cloete, Schoeman, & Muller, 2005; Snyman, Olivier, Erasmus, & Van Wyk, 1997)
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