The main objectives of the present study were to assess the genetic diversity, population structure and to appraise the efficiency of ongoing selective breeding program in the closed nucleus herd of Nellore sheep through pedigree analysis. Methods: Information utilized in the study was collected from the pedigree records of Livestock Research Station, Palamaner during the period from 1989 to 2016. Genealogical parameters like generation interval, pedigree completeness, inbreeding level, average relate dness among the animals and genetic conservation index were estimated based on gene origin probabilities. Lambs born during 2012 and 2016 were considered as reference popu lation. Two animal models either with the use of F i or ∆F i as linear covariables were evaluated to know the effects of inbreeding on the growth traits of Nellore sheep. Results: Average generation interval and realized effective population size for the reference cohort were estimated as 3.38±0.10 and 91.56±1.58, respectively and the average inbreeding coefficient for reference population was 3.32%. Similarly, the effective number of founders, ancestors and founder genome equivalent of the reference population were observed as 47, 37, and 22.48, respectively. Fifty per cent of the genetic variability was explained by 14 influ ential ancestors in the reference cohort. The ratio f e /f a obtained in the study was 1.21, which is an indicator of bottlenecks in the population. The number of equivalent generations obtained in the study was 4.23 and this estimate suggested the fair depth of the pedigree. Conclusion: Study suggested that the population had decent levels of genetic diversity and a nonsignificant influence of inbreeding coefficient on growth traits of Nellore lambs. However, small portion of genetic diversity was lost due to a disproportionate contribution of founders and bottlenecks. Hence, breeding strategies which improve the genetic gain, widens the selection process and with optimum levels of inbreeding are recommended for the herd.

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The objective of the present study was to estimate variance components and genetic parameters for average daily gain from birth to weaning (ADGa), birth to 6 months (ADGb) and 3 to 6 months (ADGc) and corresponding Kleiber ratios (Ka, Kb, and Kc) in Nellore sheep. Data were collected from the records maintained at Livestock Research Station, Palamaner, for analysis and the data spread from 1993 to 2016 (23 years). Lambing year, sex of lamb, season of lambing, and parity of dam were included in the model as fixed effects, and ewe weight was kept as a covariate. Six animal models were fitted with various combinations of direct and maternal genetic effects using restricted maximum likelihood procedure. The Akaike's information criterion was employed to determine the best model for each trait. Direct heritability estimates obtained in the study for ADGa, ADGb, ADGc, Ka, Kb, and Kc were 0.37, 0.41, 0.34, 0.48, 0.46, and 0.37, respectively, and their corresponding maternal heritabilities ranged from 0.11, 0.21, 0.11, 0.24, 0.22, and 0.11, respectively. (Co)variance among the direct and maternal effects were found to be negative in all the traits. Direct genetic correlations among the studied traits were positive with few exceptions, and they ranged from - 0.03 (Ka-Kc) to 0.99 (ADGa-Ka); similarly, the phenotypic correlations ranged from low to high - 0.18 (ADGa-Kc and Ka-Kc) to 0.95 (ADGa-Ka). These results indicated the importance of maternal effects in affecting the growth rate and efficiency of feed utilization traits and also suggested the possibility of moderate genetic progress for these traits through selection.

The objective of this study was to obtain (co) variance components and genetic parameter estimates for post-weaning body measurements such as body length, height at withers and chest girth recorded at six (SBL, SHW and SHG), nine (NBL, NHW and NHG) and twelve (YBL, YHW and YHG) months of age along with yearling weight (YW) in Nellore sheep maintained at livestock research station, Palamaner, Andhra Pradesh, India and also the association among body measurements with yearling weight was studied. Methods: Data on 2,076 Nellore sheep (descended from 75 sires and 522 dams) recorded between 2007 and 2016 (10 years) were utilized in the study. Lambing year, sex of lamb, season of lambing and parity of dam were included in the model as fixed effects and ewe weight was kept as a covariate. Analysis were conducted with six animal models with different combinations of direct and maternal genetic effects using restricted maximum likelihood procedure. Best model for each trait was determined based on Akaike's Information Criterion. Results: Moderate estimates of direct heritability were obtained for the studied traits viz., BL (0.02-0.24), HW (0.31-0.49) and CG (0.08-0.35) and their corresponding maternal heritability estimates were in the range of 0.00-0.07 (BL), 0.13-0.17 (HW) and 0.07-0.13 (CG), respectively. Positive direct genetic and phenotypic correlations among the traits and they ranged from 0.07 (YBL-YW) to 0.99 (SBL-SHG, SHG-YW and NBL-YBL) and 0.01 (SBL-YBL) to 0.99 (NBL-NHG), respectively. Further, the genetic correlations among all the body measurements and yearling weight were positive and ranged from 0.07 (YW and YBL) to 0.99 (YW and SHG). Conclusion: Strong association of chest girth at six months with yearling weight. Further, it is indicated that moderate improvement of post-weaning body measurements in Nellore sheep would be possible through selection.