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, northeast
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 (Fi) 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
−7 g per 1% Fi.
Maternal inbreeding depressions were estimated as
−17 g,
−37 g,
−346 g and
−62 g per 1%
Fi for BW, TLWB and TLWW