Population structure and effect of inbreeding on lamb growth in Bharat Merino sheep

The objective of present study was to evaluate the population structure and genetic variability in the Bharat Merino, a synthetic sheep evolved and maintained under standard farm management conditions and also to observe any possible effect of inbreeding on lamb growth and heritability estimate. The pedigree of 5723 animals born between 1975 and 2006 was available, out of which 5115 were in the population reference for which estimates were obtained. Effective number of founders (fe) was 55, representing 12.79% of the potential number of founders in population reference. The effective number of ancestors (fa) was 40 and the genetic contribution of the 14 most influent ancestors explained 50% of the genetic variability. The realized effective population size of the flock was 89.29 ± 2.13. The ratio fe/fa which expresses the effect of population bottlenecks was 1.375. The average inbreeding coefficient for the whole analyzed pedigree and for inbred animals was 2.32% and 4.8%, respectively. The average relatedness coefficient between individuals of the population was estimated to be 4.23%. The inbreeding coefficient increased with the addition of each generation to the pedigree. In the reference population, 6.69% individuals had more than 6.25% Fi. Although the levels of inbreeding in the flock were under control, looking in to the closed structure of the flock, accumulation of higher inbreeding in some individuals was inevitable. Study revealed non-significant effect of individual inbreeding or change in inbreeding on the lamb live weights, except birth weight where every one percent increase in inbreeding (Fi) was found to negatively affect the birth weight in lambs by 0.019 kg. Estimate of heritability for birth weight was little higher (0.27 ± 0.03) when inbreeding was included in the model as compared to little lower estimate (0.26 ± 0.03) where inbreeding was excluded.