Estimates of Genetic Parameters and Genetic Trends for Productive and Reproductive Traits of Doyogena Sheep in Southern Ethiopia
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Kebede H. Giorgis. (11/11/2019). 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.