Estimates of Genetic Parameters and Genetic Trends for Productive and Reproductive Traits of Doyogena Sheep in Southern Ethiopia

Abstract

The objective of this study was to estimate the genetic parameters and genetic trends for growth and reproductive traits of Doyogena sheep. Records used in the study were collected over a period of 6 years (2013-2018) from the ongoing Doyogena sheep community-based breeding program (CBBP). Studied traits were birth weight (BWT), 3-month weight (WWT), 6-month weight (6WT), average daily gain from birth to weaning (ADG0-3),average daily gains from weaning to 6-month age(ADG3-6), average daily gain from birth to 6-month age(ADG0-6), litter size(LS), lambing Interval(LI), age at first lambing(AFL) and annul reproductive rate(ARR). (Co) variance components and genetic parameters were estimated using the restricted maximum likelihood (REML). The analyses were carried out using WOMBAT programme. Mixed animal models of univariate and repeatability analyses were applied to estimate genetic parameters. 6 different animal models were fitted by including or excluding maternal additive genetic effects, maternal permanent environmental effect, and covariance between direct-maternal additive genetic effects. A log-likelihood ratio test (LRT) and Akaike’s Information Criterion (AIC) were used to select the most appropriate univariate model for each trait. Bivariate and multivariate analysis were applied for correlation estimates. The overall least square mean ± standard errors (LSM±SE) of lamb body weight for BWT, WWT and 6WT were 3.05±0.02 kg; 14.8±2.49 kg and 22±0.22 kg respectively. The overall LSM±SE of ADG0-3, ADG3-6, and ADG0-6 were 130.37±2.27gm, 80.59±3.62gm and 106.18±1.7gm respectively. The least square means for reproductive traits in terms of LI, ARR, LS and AFL were 281.22 ±8.8 days, 2.16 ± 0.06 lamb, 1.75±0.02 lamb and 437.43±31 days respectively. Based on the best fitted models, the direct heritability estimates, for BWT, WWT, 6WT, ADG0-3, ADG3-6 and ADG0-6 were 0.33±0.06, 0.31±0.06, 0.14±0.06, 0.13±0.04, 0.11±0.07, and 0.023±0.05 respectively. Direct heritability estimates for LS, LI and AFL were 0.28±0.12, 0.20±0.51 and 0.001±0.56 respectively. The maternal heritability estimates for BWT and WWT were 0.24±0.12 and 0.6±0.07 respectively. BWT has weak genetic and phenotypic correlation almost all the traits. The estimate of genetic correlations between WWT and 6WT, WWT and ADG0-3, WWT and ADG3-6, WWT and ADG0-6 were 0.52±0.09, 0.95±0.03, -0.23±0.13 and 0.53±0.12 respectively. The genetic correlations between LI with LS was moderate and negative (-0.44±0.9). All growth traits were negatively correlated with LS. Repeatability estimated for LS and LI were 0.61 and 0.26 respectively. Genetic changes over the selection period were 0.00085 kg,0.30 kg,0.151 kg 2.56gm, -0.37gm,0.09 gm, for BWT, WWT, 6WT, ADG0-3, ADG3-6, and ADG0-6, respectively. The genetic changes for LS, LI and AFL over the selection period were 0.002 lambs, -1.69 days and 0.09 days respectively. Genetic progress for most of studied traits has shown promising improvements. Thus, continuation of selection therefore recommended for bringing further improvement in the performance of Doyogena sheep. Estimated direct heritability for growth traits decrease as lamb age increase thus, selection based on earlier body weight will be more efficient. The LS trait suggest that selection based on litter size/number of lambs born per ewe can be effective in improving reproductive performance in Doyogena ewes.