Analysis of survival curves in seasonally mated pastoral goat herds in northern Kenya using logistic regression techniques |
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| Authors: | Ingo Hary |
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| Institution: | Institut für Nutztierwissenschaften, Fachgebiet Nutztierökologie, Humboldt-Universität zu Berlin, Philippstraße 13, 10099, Berlin, Germany |
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| Abstract: | In order to assess the effect of controlled seasonal breeding on survival performance of pastoral goat flocks, a systematic breeding programme was initiated in a herd of small East African goats over a period of 4 years in Isiolo District, northern Kenya. This papers presents an analysis of survival rates observed in six different mating seasons. The statistical analysis is based on modelling hazard functions parametrically over time using logistic regression and polynomial spline functions. With respect to kid survival, litter size and parity of dam failed to reach statistical significance after adjustment was made for the effects of birth weight and milk yield until weaning. Highly significant interactions were found between time factors and the effect of mating season, indicating non-proportionality of death risks across mating seasons. Confining mating to the period between June and November is likely to confer a distinctive advantage in terms of young livestock survival. In contrast, joining does during the short dry season leads to kid mortality rates of about 50%, and should therefore be avoided. Doe survival was evaluated in terms of mating season, production cycle, parity, and reproductive status. The ranking of mating season groups with respect to doe survival was similar to that observed in kids, although the differences were much smaller and non-significant. The lowest annual mortality rate was observed when breeding females were mated during the long dry season. It is concluded that confining breeding to the long dry season can be an effective management intervention to reduce mortality rates in pastoral goat flocks. |
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| Keywords: | seasonal breeding goats survival performance pastoral systems northern Kenya |
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