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Cows feel the heat

Animal Behavior

Climate Change Analysis
Photo: HOT COWS: Climate change can cut milk production by 280 litres of milk annually for each cow.
March 05, 2007
Six years ago, CSIRO scientists Roger Jones and Kevin Hennessy studied the potential impact of heat stress caused by climate change on dairy cattle at farms around Muswellbrook in the Hunter Valley of NSW.
Cool cows produce more milk, and when summer temperatures soar above 35 degrees, hot cows are less able to cool themselves by increasing their respiration rate or dilating blood vessels. A hot dairy cow is a very distressed cow, and severe heat stress can kill dairy cattle and their embryonic calves.
According to a study by dairy scientists at Virginia State University in the United States, heat stress in dairy herds is "associated with difficult births, heat exhaustion, fatty liver and mastitis, as well as adverse reactions to vaccinations leading to abortions and death". The study also found heat stress "can contribute to lameness, perhaps due to acidosis or increased output of bicarbonate".
Heat-stressed cattle eat less frequently and feed during cooler times of the day, but they eat more at each feeding. As temperatures rise, the cows' respiratory rate increases "with panting progressing to open-mouth breathing" and a rapid loss of carbon dioxide.

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