Effects of Heat Stress on Reproductive Parameters, Milk Quality, and Cow Activity in Lactating Holstein and Jersey Dairy Cows

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Coleman, Erin
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University Honors College, Middle Tennessee State University
Heat stress can negatively affect pregnancy rate, conception rate, and milk quality in dairy cattle. Heat stress is one of the major challenges dairy farms face due to the negative effects heat stress plays on production. The objective of this study was to determine if there is a relationship between heat stress and cow reproductive parameters, cow activity, and milk quality in Holstein and Jersey cows. Two groups of cattle consisting of both Holstein and Jersey cows were evaluated over 2 seasons: summer (July and August) and winter (December and January) for heat stress. Cows were monitored through DHIA data to analyze somatic cell count, milk yield, conductivity, average rest time, average rest bouts, and average activity. Temperature Humidity Index (THI) was also calculated to show if the lactating herd was suffering from heat stress. Cows were under mild to moderate heat stress during the summer months of July and August. During the winter months of December and January, cows did not suffer from heat stress. In the summer, cows had increased restless activity due to heat stress which can have negative effects such as lower milk production and increased chances of lameness.