Survival Analysis Of The Red Maasai And Dorper Lambs

Abstract

The Red Maasai and Dorper lambs born from 1991-1996 in Coastal region of Kenya (Diani Estate) were compared using survival analysis. The Red Maasai lambs had a lower risk of death (i.e., relative risks of 0.28 and 0.26 in pre-weaning and post-weaning periods respectively) compared to the Dorper (i.e., the standard) when a standard Cox model was fitted to the data. When a frailty term was fitted, there was little change in the value of the parameter estimates. The deaths of the Dorper lambs were higher compared to those of the Red Maasai with the contribution of mis-mothering being about 32% for Dorper lambs and about 30% for Red Maasai and endoparasites being about 16% for Dorper and about 9% for Red Maasai lambs in pre-weaning period. In post-weaning period, the proportions of deaths for endoparasites were about 41% for Dorper and about 33% for Red Maasai while pneumonia contributed about 17% of the deaths of the Dorper and about 7% of the deaths of the Red Maasai lambs. There were significant effects due to birth weight and weaning weight. The age of the dam was not significant in pre-weaning period but from the standard and frailty Cox models, the lambs born to older ewes had a lower risk of death compared to those born to younger ewes. The most frail lambs tend to die m~re as compared to the stronger lambs in both the pre-weaning and post-weaning periods with these differences in deaths becoming more pronounced in post-weaning period.