Abstract:
The data set employed in this study was comprised of a number of 6,800 records of
lamb’s longevity and their survival rate, collected from 1989 through 2009, from the LoriBakhtiari
experimental flock at the Shooli Station in Shahrekord, Iran. The data were
analyzed using linear models and proportional hazard models with Weibull function.
These models included fixed factors and direct additive genetic, maternal additive genetic,
maternal common environmental and residual random effects. Genetic parameters were
estimated using Restricted Maximum Likelihood (REML) procedure fitting a sire model
as well as animal models including different combinations of direct and maternal effects.
Estimates of direct heritabilities of longevity and survival rate from different linear
models were low (0.01 to 0.09). The maternal heritability ranged from 0.00 to 0.04, and
decreaced with increase in the age of lambs. The estimates of heritability in logarithmic
scale, original scale and effective heritability obtained from the sire and animal models
with Weibull function were medium to high (0.08 to 0.55) and were higher than those
estimated through different linear models. The maternal heritability estimated through
Weibull models decreased with the age of lambs (0.25 to 0.01). These results indicated that
the accuracy of the Estimated Breeding Values (EBV) of lambs’ survival rate from birth
up to yearling age, using linear animal models vs. proportional hazard models, would be
low vs. medium to high, respectively. Both animal and maternal genetic effects should be
considered in the models for improving the survival rate up to 4 months of ages.
Keywords: Heritability, Linear model, Lori-Bakhtiari lamb, Survival, Weibull function.
