Abstract :
Reproductive records of 5373 Lori-Bakhtiari ewes were collected from a research flock at the Lori-Bakhtiari sheep breeding station
during 1989–2005. Genetic parameters were estimated for six basic and six composite traits. The basic traits were conception rate
(CR), total number of lambs born (NLB), number of lambs born alive (NLBA), number of lambs alive at weaning (NLAW), litter
mean weight per lamb born (LMWLB) and litter mean weight of lambs at weaned (LMWLW). The composite traits were number
of lambs born per ewe exposed (NLB/EE =CR×NLB), number of lambs weaned per ewe exposed (NLW/EE =CR×NLWA), total
litter weight at birth (TLWB= NLB×LMWLB), total litter weight at weaning (TLWW=NLAW×LMWLW), total litter weight at
birth per ewe exposed (TLWB/EE =CR×TLWB) and total litter weight at weaning per ewe exposed (TLWW/EE=CR×TLWW).
A derivative-free algorithm was used to obtain REML estimates of genetic parameters. Fitting a multi-trait animal model included
fixed effects and also random effects due to animal direct genetic effects, permanent environment effects due to repeated record of
ewe and residual effects. Estimates of heritabilities for animal genetic effects were mainly small (0.01–0.19) due to the typical high
influence of environmental factors on reproductive traits and non-normal distributions of some traits. Estimates of repeatabilities for
animal permanent environmental effects were small to medium (0.09–0.24). Genetic correlations ranged from −0.58 to 0.98 among
traits. Phenotypic correlations ranged from −0.25 to 0.38 among traits. Some estimates of genetic correlations (such as CR with
some traits) do not seem to have a biological explanation. These estimates of genetic parameters may provide a basis for deriving
selection indexes for reproductive traits.
© 2007 Elsevier B.V. All rights reserved.
