Abstract
ABSTRACTThe objective of this study was to estimate genetic parameters for longevity and survival traits from birth to yearling in Moghani breed of sheep. The data set comprised of 4580 lamb survival records collected during 1994 to 2012 in the breeding station of Moghani sheep. Traits studied were cumulative lamb survival from birth up to 3 (S1), 6 (S2), 9 (S3) and 12 (S4) months of age, and corresponding longevity of lambs (L1, L2, L3 and L4, respectively). The linear and threshold animal model analyses were run using a restricted maximum likelihood method and average information algorithm (AIREML) of the WOMBAT software and MATVEC program, respectively. Also, cumulative survival traits were analysed using the sire model through the Weibull proportional hazard function of the MATVEC program. Direct heritability estimates obtained from different linear models varied from 0.004–0.021, 0.014–0.023, 0.058–0.069 and 0.006–0.061 for L1, L2, L3 and L4, respectively. Also, heritability estimates on the logarithmic scale for S1, S2, S3 and S4 obtained from the Weibull sire model were 0.57, 0.40, 0.08 and 0.03, respectively. Medium to high estimates of heritability for survival traits, employing proportional hazard models, suggest that lamb survival could be improved through direct selection within the flock.
Highlights
Survival of lambs is a compound character affected by many various effects connected to weather conditions, management, lamb and ewe behaviour, and other environmental factors (Smith 1977; Christley et al 2003; Everett-Hincks et al 2005; Tomaszyk et al 2014; Aktaş et al 2015; Moraes et al 2016)
Low survival rates of lambs may perform as a hindrance to obtaining greater reproductive efficiencies because the profit of increasing the litter size at birth is frequently neutralized by lamb survival decreases related to an increase in multiple births (Slee et al 1991)
Estimates of direct and maternal heritabilities, ratio of maternal permanent environmental variance to phenotypic variance, correlation between direct and maternal genetic effects and AIC values for longevity and survival traits from birth up to yearling obtained under different linear models are shown in Tables 1 and 2, respectively
Summary
Survival of lambs is a compound character affected by many various effects connected to weather conditions, management, lamb and ewe behaviour, and other environmental factors (Smith 1977; Christley et al 2003; Everett-Hincks et al 2005; Tomaszyk et al 2014; Aktaş et al 2015; Moraes et al 2016). Breeding programmes with the objective of enhancing reproductive efficiency should be improved to keep the rate of alive births (increasing survival rate) (Brien et al 2010). Lamb survival and ewe longevity would be improved by implementing genetic selection programmes and through improved management interventions In this regard, understanding the genetic parameters of longevity and lamb survival is necessary to evaluate the possibility of including these traits into the selective breeding programmes within sheep populations. The objective of current study was to estimate genetic parameters of the longevity and survival traits from birth to yearling in Moghani breed of sheep using proportional hazard models through the Weibull function, linear and threshold models of analysis
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