Evaluation of models for estimation of genetic parameters for post-weaning body measurements and their association with yearling weight in Nellore sheep.

Objective: 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.