Genetic Parameters for Direct and Maternal Effects on Pre-Weaning Growth and Efficiency-Related Traits in Inter-Cross Lamb.

The objective of this investigation was to estimate the (co)variance components and genetic parameters for pre-weaning growth traits in inter-cross sheep maintained at NTRS, ICAR-CSWRI, Garsa, India. Data records of 1891 lambs for birth weight (BW) and 1763 lambs for weaning weight (WW) descending from 183 rams and 667 dams, born between 2012 and 2023, were utilised in the study. The live weight was used for the calculation of pre-weaning average daily weight gain (PDWG), pre-weaning Kleiber ratio (PKR), pre-weaning growth efficiency (PGE) and pre-weaning relative growth rate (PGR). The fixed effects used in the model were birth year, genetic group, sex, type of birth, and parity of dam. Estimation of covariance components was carried out by fitting a series of animal models using the average information restricted maximum likelihood (AIREML) algorithm. The best-fitting model was determined after testing for improvement in log-likelihood values. The overall LSM ± SE for BW, WW, PADG, PKR, PGE, and PGR were 3.29 ± 0.04 kg, 14.83 ± 0.22 kg, 127.87 ± 2.46 g, 16.78 ± 0.13, 357.53 ± 7.13, and 1.66 ± 0.02, respectively. Analysis revealed that pre-weaning traits were significantly (p < 0.05) affected by year of birth, parity of dam, type of birth and sex of the lamb. Direct heritability estimates were 0.11 ± 0.04, 0.16 ± 0.04, 0.16 ± 0.04, 0.15 ± 0.06, 0.18 ± 0.06 and 0.17 ± 0.06 for BW, WW, PADG, PKR, PGE, and PGR, respectively. The corresponding maternal heritability estimates for BW, PKR, PGE, and PGR traits were 0.19 ± 0.03, 0.11 ± 0.04, 0.13 ± 0.04, and 0.12 ± 0.04, respectively. For WW and ADWG, only direct effects were significant. The correlations of WW with efficiency-related traits and among the other traits were quite high and positive. Significant impact of maternal care for early growth traits in this breed indicates the importance of considering both direct and maternal effects for genetic evaluation. The moderate estimate of heritability for WW with high and positive genetic correlations with other traits, makes this trait a candidate for selection in the present flock. We therefore recommend the use of WW as a single trait selection criterion for the overall improvement of the growth traits in the sheep flock.