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An Epidemiologic Study of the Summer Rise in Bulk Milk Somatic Cell Count in Ontario Dairy Herds

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Title: An Epidemiologic Study of the Summer Rise in Bulk Milk Somatic Cell Count in Ontario Dairy Herds
Author: Shock, Daniel
Department: Department of Population Medicine
Program: Population Medicine
Advisor: Kelton, DavidLeBlanc, Stephen
Abstract: Study objectives were to: a) explore and describe the seasonal SCC fluctuation, over several years, in Ontario dairy herds; b) describe the relationship between on-farm summer weather conditions with that of the closest official meteorological station, and determine the appropriateness of using meteorological station data as a surrogate for on-farm environment monitoring; c) conduct a prospective case-control study to evaluate farm-level risk factors contributing to a summer rise in somatic cell count (SCC); d) describe attitudes, motivations, and perceptions held by a subset of Ontario dairy producers towards udder health. A working definition of what constitutes a high summer increasing (HSI) herd was developed. Herds that were smaller, produced low average BMSCC, filled less of their production targets, and had a recent history of high seasonal variability had higher odds of high summer elevations. Environmental conditions measured inside dairy facilities exhibited a wide degree of variability when compared to measurements made at the closest meteorological station. Tie stall housing, pasture access, and inadequate ventilation strategies all contributed to higher daily mean and maximum daily temperature-humidity index (THI) readings within the barn. After controlling for these factors, THI within the barn environment remained higher than conditions recorded at weather stations. Using weather station environmental data is not an accurate proxy for on-farm conditions. When evaluating on-farm risk for experiencing HSI, increased time in the pen of intended calving, both pre- and post- calving, was associated in decreased odds of experiencing an elevation in SCC over the summer, along with an increased number of cows milked per hour and inconsistent application of premilking udder preparation. The diagnosis of clinical and subclinical Streptococcal infections increased the odds of experiencing an elevation in SCC. Participating dairy producers generally had high levels of self-efficacy beliefs when it came to udder health management, although there was still the perception that, under certain situations, mastitis is uncontrollable. Participants identified financial benefits and penalties as potent motivators to lower their herd SCC. Finally, the results bring to light the effects that increased regulations can have on the level of frustration and isolation perceived by dairy producers.
Date: 2014-06
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