Genetic parameter estimates for reproductive traits in Chokla ewes of India

Genetic evaluation of early reproductive traits of Harnali sheep

The aim of this study is to examine early reproductive traits and assess genetic parameters associated with them in Harnali crossbred ewes through Bayesian inference. The dataset encompasses 555 reproduction records spanning 24 years from 1998 to 2021. The traits under investigation include age at first lambing (AFL), weight at first lambing (WFL), and first lambing interval (FLI). First, least-squares modeling was conducted, incorporating fixed effects such as the period of birth and the dam's weight at lambing for the targeted traits. Subsequently, Bayesian estimation involved a series of animal models that accounted for direct additive effects, with or without maternal effects, along with significant fixed effects. The overall least-squares mean for AFL, WFL and FLI was observed as 851.49 ± 12.20 days, 27.5 ± 0.16 kg, 455.04 ± 10.66 days, respectively. The period of birth significantly influenced AFL and WFL, while the dam's weight at lambing showed a significant association with WFL only. Bayesian estimates revealed low direct heritability for AFL, WFL, and FLI, ranging from 0.12, 0.16 and 0.04, suggesting limited potential for improvement through selection. However, maternal effects accounted for a proportion of phenotypic variance ranging from 0.04 to 0.14 across these traits. It was concluded that enhancing reproductive efficiency in Harnali ewes would require a greater focus on management aspects, particularly feeding and breeding practices, while also considering maternal influences within the existing breeding plan.

Influence of maternal and additive genetic effects on lamb survival in Harnali sheep

Lamb survival is a critical aspect in the sheep industry as it increases the chances of economic gain in the flock. The objective of the current study was to assess the incidence of lamb mortality in Harnali sheep and to estimate maternal and additive genetic effects of lamb survival using the data of 2057 lambs born to 134 sires and 623 dams for the period of 20 years (2001-2020). The genetic evaluation was carried out using threshold animal models comprising direct and maternal effects using THRGIBBS1F90 and POSTGIBBSF90 programs. Cumulative mortality (95% CI (confidence interval)) for the S1 (lambs which died up to weaning age), S2 (lambs which died from birth to 6 months of age) and S3 (lambs which died from birth to 12 months of birth) groups was 8.41 (7.21-9.61), 14.10 (12.59-15.60) and 17.70 (16.05-19.34) %, respectively. The logistic regression analysis revealed significant (p < 0.05) influences of non-genetic factors and indicated that the female lambs, heavier dam and higher birth weight of lamb were associated with better survival as compared to their counterparts. The estimates of direct additive heritability for S1, S2 and S3 were 0.04 ± 0.01, 0.07 ± 0.03 and 0.11 ± 0.04, respectively. In addition to this, significant influences of the maternal permanent environmental effects were observed for lamb survival up to weaning as well as six months of age. Thus, the present findings suggest that lamb survival could be improved through better management practices but consideration of maternal permanent environmental effects is important for initial survival of the lamb.

Bayesian estimation of the genetic relationship of survival traits from birth to yearling age with birth weight in Guilan sheep

This study aimed to estimate genetic parameters for cumulative survival traits from birth to yearling age and to estimate their genetic relationship with birth weight in Guilan sheep. The dataset used in this study comprised 41,037 survival records of Guilan lambs born from 496 sires and 10,256 dams, collected by the Guilan Province Agricultural Jihad Organization (in Rasht, Iran) during 1990-2013. The data included complete pedigree information; gender; year, month, and day of death; dam age; year, month, and day of birth; birth type; and birth weight. Cumulative survival traits from birth to yearling age were analyzed using threshold animal models via the Bayesian method. Also, linear-threshold animal models were used to study the genetic relationship between survival at different ages and birth weight. Direct heritability estimates of cumulative survival from birth to 60, 90, 180, 270, and 365 days of age were low and equal to 0.17, 0.16, 0.08, 0.04, and 0.04, respectively, and the corresponding maternal heritability estimates were 0.21, 0.18, 0.15, 0.08 and 0.08, respectively. Mean estimates of direct genetic correlations between birth weight and survival traits were medium (from 0.22 to 0.28). To improve the survival traits, more emphasis must be put on the amelioration of the non-genetic factors affecting it. Indirect selection based on traits high genetically correlated with survival could increase the survival rate in Guilan lambs.