Strategic elements for genetic improvement of survival traits in Timahdite lambs

• Genetic study for improvement of survival traits in Timahdite lambs.
• Genetic analysis using logistic, probit, and complementary log–log link functions.
• Rate risk of mortality related to each level of explanatory fixed effects.
• Improvement of flock management practices will increase the lamb’s survival rate.
• Improvement of survival traits by indirect selection using the average daily gain.

Lamb survival in Timahdite sheep was analyzed using survival records from 79,565 lambs born between 2001 and 2012 in 37 flocks in the breeding program of National Association of Sheep and Goats (ANOC) in Morocco. Traits analyzed were lamb survival from birth to 10 (S10), 30 (S30), and 70 days of age (S70) and to weaning age (SW). The corresponding averages of survival were 97, 96, 90, and 86%, respectively. Hazard ratios obtained by the Cox model showed that male lambs, twin-born lambs and winter-born lambs were less likely to survive than female lambs, single-born lambs and autumn-born lambs, respectively. The heritability estimates obtained using the logistic and probit scales were low to moderate (0.01–0.18), while they were low (0.01–0.08) using the complementary log–log scale. Phenotypic and genetic correlations between lamb survival traits varied from 0.10 to 0.82 and from 0.09 to 0.90, respectively. The phenotypic correlations between lamb survival traits and average daily gains (ADG) between the last two weights above mortality were low and they increase from −0.02 for S10 to 0.24 for SW. At the genetic level, a negative correlation but weak was recorded between ADG and S10 (−0.19). ADG was slightly correlated with S30 (rg = 0.08) and S70 (rg = 0.24) and moderately correlated with SW (rg = 0.41). Annual genetic change for lamb survival, expressed relatively to overall means, amounted to +0.0014, −0.0105, and −0.0176% per annum from birth to 30 days, to 70 days and to weaning age, respectively. The results of this study suggest that to improving survival, it is necessary to combine the direct selection and improvement of breeding conditions of lambs.