Pedigree analysis of Iran-Black sheep and inbreeding effects on growth and reproduction traits

Abstract

Pedigree information and data on growth and reproduction traits in Iran-Black sheep breed, collected during a period of 28 years (1980–2008) in Abbasabad breeding station, north-east of Iran, were used to genealogical characterization of the breed using pedigree analysis and investigation the effect of inbreeding on growth related traits including birth weight (BW) and weaning weight (WW) and reproduction traits including litter size at birth per ewe lambing (LSB), litter size at weaning per ewe lambing (LSW), total litter weight at birth per ewe lambing (TLWB) and total litter weight at weaning per ewe lambing (TLWW). The Iran-Black is a composite breed; the first cross of Chios rams with Iranian Baluchi ewes. Inbreeding depression was investigated for all the studied traits by fitting individual increase in inbreeding coefficient (ΔFi) of the lambs and the ewes as linear covariates under univariate animal models. The average inbreeding coefficient during the study period for all and inbred animals were 8.08% and 9.90%, respectively. The animals born in the last 3 years (2006–2008) were considered as reference population and genealogical analysis was performed. The values of effective population size estimated from the individual increase rate in coancestry and the individual increase in inbreeding were 28 and 27, respectively. Genealogical parameters estimated based on the probabilities of gene origin including the effective numbers of founders, the effective numbers of ancestors, the effective numbers of founder genomes (founder genome equivalents) and the effective numbers of non-founder genomes were estimated as 13, 11, 6 and 12, respectively. Generation interval (in years) and the average equivalent complete generation were 3.39 and 7.10, respectively. Significant individual inbreeding depression was only found for BW (P<0.05) as −7g per 1% ΔFi. Maternal inbreeding depressions were estimated as −17g, −37g, −346g and −62g per 1% ΔFi for BW, TLWB and TLWW (P<0.01) and WW (P<0.05), respectively.