Lamb survival in sheep breeds on New Zealand hill country

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Abstract
Data on lamb survival (lambs weaned/100 lambs born) on hill country from 1969–76 were analysed. The breeds were Romney, Coopworth, Perendale, Cheviot, Dorset-Romney, Drysdale, High Fertility Perendale, Corriedale, Merino, and Merino-Romney. Not all breeds were present in each year. Birth weight, year born, breed, and sex of lamb had significant effects on survival, as did age of dam. Birth rank effects on survival could be explained by birth weight, as could much of the variation caused by age of dam. Overall mean survival was 83% for singles and 73% for multiples. Most lambs died at birth or at 1 to 3 days of age. Within birth ranks the most frequent causes of death were dystocia among singles and starvation-exposure among multiples. Incidence of dystocia tended to increase with increasing birth weight whereas incidence of loss due to starvation-exposure increased with decreasing birth weight. Breed differences were apparent in dystocia but they were small compared with birth rank effects, Lambs of birth weight from 3.5 to 5.5 kg and from the older age groups of dams (4-year and 5-year) survived best.

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