Effects of inbreeding on reproduction and fitness traits in a closed flock of Nilagiri sheep, an endangered Indian breed

The objective of this study was to investigate the effect of inbreeding on reproductive and fitness traits in Nilagiri sheep. Information on pedigree of 6430 animals collected during the year of 1965-2015 by Sheep Breeding Research Station (SBRS) in Sandynallah were used for analysis. Inbreeding coefficient (F) was calculated from pedigree information using Wright's method. The average inbreeding per cent was 1.82% in the whole popu-lation studies (6430 animals). The average inbreeding per cent was 3.9% for 3007 no. of inbred animals. The effect of inbreeding on most of the reproduction and fitness traits were significant and depression due to inbreeding was evident.The significant effect of inbreeding on reproduction traits viz., age at first service (AFS), weight at first service (WFS), age at first lambing (AFL) and fitness traits viz., tupping percent (TP), number of lambs weaned per ewe mated (NLWEM), number of lambs weaned per ewe lambing (NLWEL) and total lambs weaned per ewe over lifetime (TLWE) was studied using a general linear model, with individual inbreeding coefficient as covariate. The partial regression coefficient for AFC, WFS, AFL, TP, NLWEM, NLWEL and TLWE were 1.28 days,-0.25 kg, 8.13 days, -0.02%, -0.028,-0.017 and-0.182 per 1 per cent increase in inbreeding for Nilagiri sheep. Survival and litter size were not affected by inbreeding. In general, inbreeding had a depressive effect on most of the reproduction and fitness traits. Inbreeding in the population has to be restricted through methods such as introduction of unrelated animals or following co-ancestry based mating system.