Mortality rate of Boer, Central Highland goat and their crosses in Ethiopia: Nonparametric survival analysis and piecewise exponential model.

BACKGROUND

Analysis of survival data by linear or logistic model ignores censoring and skewness inherent in the mortality data. The objective of this study is to estimate the morbidity and mortality rates of kids and adult goats, identify important risk factors for mortality using survival analysis and summarise important causes of goat death.

METHODS

Nonparametric survival analysis and a piecewise exponential model (PEM) were used.

RESULTS

The mortality rates of kids and adult goats were 0.629 and 0.302 per animal year, respectively. The 25th, 50th and 75th percentiles of survival time of kids were 5, 162 and 1300 days, respectively, and those of adults and goats were 280, 828 and 1,735 days, respectively. Gastrointestinal-related diseases, pneumonia, weak kid, agalactia, mismothering and heartwater (cowdriosis) were the most important causes of mortality. Constant piecewise exponential regression analysis of risk factors indicated that breed, kid birth weight, doe post-partum weight (PPWT), birth type, birth year and precipitation variables were associated with (p-value < 0.05) kid mortality rate. Pure Boer kids compared with Central Highland goat cross with Boer goats were 2.505 times at a higher probability of mortality (p-value < 0.001). A 1-kg increase in kid birth weight and dam PPWT reduces mortality probability by 32.5% (p-value = 0.000) and 6.4% (p-value < 0.001), respectively. Twin birth kids had a 1.512 times higher rate of mortality (p-value = 0.001) than single-born kids. A 1-ml increment of 15 days of average precipitation significantly reduced kid mortality by 7.8% (p-value < 0.001).

CONCLUSION

Vaccination, extensive control of ticks and the use of proper comfortable housing to reduce the stress of goats are recommended. Scheduling a mating programme (May to early July) to match the kidding period to the less kid mortality seasons (end of the long rainy season) of flocks is also important to reduce kid mortality.