The epidemiology of culling and mortality of New Zealand dairy cows : a thesis presented in partial fulfilment of the requirements for the degree of PhD in Veterinary Epidemiology at Massey University, Manawatu, New Zealand

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Massey University
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Culling of dairy cattle for non-production causes and on-farm mortality have adverse consequences for farm profitability and animal welfare. Farmers face increasing pressures to improve farm profit and to answer concerns from the public and consumers about the welfare of their animals and ethics of their management systems. Farmers in New Zealand need new information to both develop control programs to reduce losses that arise from non-production culling and mortality, and to promote and defend their farming system. Our main aims were to define the current and past trends in the incidence of culling and mortality in New Zealand dairy cows, and investigate their associated risk factors. Our secondary aims were to review the incidence of culling and mortality in dairy cattle in other modern dairy industries against which the findings from New Zealand studies could be compared, to evaluate any limitations for analysis of electronic database records of culling and mortality of New Zealand cows, and, to estimate the financial consequences for herd owners of reduced incidence of non-production culling and mortality. We found no trend over the last two decades in the incidence of culling of dairy cows, either internationally or nationally, whereas, over the same period, the incidence of mortality in cows has increased internationally, but not in New Zealand. Additionally, we identified several disorders especially common in the period immediately following calving associated with increased rates of culling and mortality; that electronic database records of cows that had been culled or died were suitable for analysis when they came from a large population, but could be biased from individual herds; and that farm profits were increased when the incidence of culling and mortality was reduced. These findings provide new information to support New Zealand dairy farmers to develop their own performance targets and control programs to reduce the incidence of mortality and non-production culling of cows.
Dairy cattle, Mortality, New Zealand