Genetic Variability of Bharat Merino Sheep Derived from Pedigree Information

Background: The genetic variability in a population is the raw material for selection, because the estimation of genetic parameters depends on the variability present within the population. The pedigree analysis is a method to assess population genetic variability. An increase in the level of inbreeding disturbs the production performance of the animals. Hence, it is essential to assess the effect of inbreeding on production performance of the animals at regular intervals. The present study was conducted on data of Bharat Merino (BM) sheep with twin objectives of evaluating the population structure by pedigree analysis and possible effect of inbreeding on lamb growth and heritability estimates. 
Methods: The study was conducted on data consisting of a total of 9688 pedigree records of BM sheep born from 1975 to 2018 (43 years), out of which 9050 formed population reference (with both the parents known). ENDOG ver 4.8 program was used to generate different measures of genetic diversity. General Linear Model of SPSS 25.0 was used to ascertain the effect of inbreeding (Fi) or change in inbreeding (ÄFi) on the lamb live weights. Using animal model with software WOMBAT, single trait linear mixed model analyses were performed. The heritability estimates and breeding values were obtained by including or excluding the inbreeding coefficient in the model to observe how the estimates of heritability varied with inclusion or exclusion of the inbreeding coefficient. 
Result: Effective number of founders (fe) was 56, constituting 11.39% founders in the population reference, while the effective number of ancestors (fa) was 43.The genetic contribution of the 15 most influent ancestors explained 50% of the genetic variability in the dataset. The ratio fe/fa, representing the effect of population bottleneck, was 1.302. The average inbreeding coefficients for the whole pedigree was 2.36%, while it was 3.84% for inbred animals. It was found that the inbreeding coefficient (Fi) increased with the addition of each generation to the pedigree. The average relatedness coefficient was 4.53% between members of the population.The effect of individual inbreeding (Fi) or the change in inbreeding (DFi) was not significant on the lamb live weights, except the effect of individual inbreeding (Fi) on three-month body weight and average daily gain (0-3month) and of change in inbreeding (DFi) on three-month body weight. From the analysis of the pedigree data of Bharat Merino sheep, it was found that the most of the measures of genetic diversity were within acceptable limits and the pedigree data was reasonably well maintained. When inbreeding was accounted for in the model, there were reductions in h2 estimates as well as the estimates of breeding values for both 3WT and ADG1 and consequently there were changes in ranking of animals for both 3WT and ADG1.