Browsing by Author "Compton, Christopher William Raymond"

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    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
    (Massey University, 2018) Compton, Christopher William Raymond
    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.
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    Epidemiology of mastitis in peripartum dairy heifers : a dissertation presented in partial fulfilment of the requirements for the degree of Masters of Veterinary Studies in Epidemiology at Massey University, Palmerston North, New Zealand
    (Massey University, 2006) Compton, Christopher William Raymond
    An observational field study was conducted on 708 heifers in 30 spring-calving dairy herds in the Waikato region of New Zealand. The aim of the study was to describe patterns and determinants of intramammary infection (IMI) and clinical mastitis (CM) in the peripartum period. Mammary secretion samples for bacteriological testing were taken from all quarters approximately 3 weeks prior to the planned start of the calving period and within 5 days following calving, in addition to quarters diagnosed with CM within 14 days of calving. Pre-calving IMI was diagnosed in 18.5% of quarters, and of these coagulase negative staphylococci (CNS) were the predominant isolate (13.5% of quarters). Post-calving, Streptococcus uberis (S. uberis) prevalence increased four-fold to 10.0% of quarters. Prevalence of all pathogens decreased rapidly following calving. Clinical mastitis cases were predominantly associated with S. uberis. The hazard of diagnosis was higher in heifers than other parity groups combined and highest in the first 5 days of lactation. Intramammary infection was associated with an increased risk of removal from the herd and high somatic cell count (> 200 000 cells/ml) at subsequent herd tests, but neither CM nor IMI were associated with reduced milk yield or milk solids production. Multilevel logistic regression models in combination with path analysis were used to investigate postulated causal pathways between risk factors for CM and subclinical mastitis (SCM) post-calving. Significant risk factors for SCM were found to be pre-calving intramammary infection (IMI), low minimum teat height above the ground and poor udder hygiene post-calving. Significant risk factors for CM were pre-calving IMI, Friesian breed, low minimum teat height above the ground, udder oedema, and low post-calving non-esterified fatty acid serum concentration. Possible causal pathways for SCM and CM are discussed, and preventive measures against both environmental exposure and host factors recommended.