Heat stress affecting cows' fertility, study finds
Higher temperatures have a major impact on cows' fertility, according to new research that reveals the potential impact of climate change on livestock. Since the mid 1980s, the reproductive efficiency of dairy herds has fallen sharply, despite advances in genetics and the management of herds. Many factors affect the fertility rate of cattle, and in this latest study, scientists from the Autonomous University of Barcelona in Spain studied the impact of heat stress on conception rates. Heat stress occurs when the environmental temperature, radiant energy, humidity and wind speed create conditions that are hotter than those of the temperature range of the animal's thermal neutral zone. The scientists analysed data from over 10,000 inseminations from four herds over a three year period. Using climate data from a nearby weather station, they worked out levels of heat stress in the days immediately before and after each insemination. They found that high levels of heat stress at key points reduced the likelihood of a successful conception. For example, high heat stress three days before insemination reduced fertility, probably due to ovulation failure. Ovulation failure was 3.9 times higher in cows inseminated during the warm period (May to September) than the cooler part of the year. Heat stress on the day of insemination itself is also important, as heat stress could affect eggs, sperm and embryos. Furthermore, a high maximum temperature the day after insemination also reduced conception rates. The researchers conclude that climate factors seem to be highly relevant for conception rate. They recommend that farmers check both temperature (including maximum temperature) and humidity and know when to put cooling measures in place. In the study, only maximum daily temperatures of 20°C and below led to an increase in fertility. The study is published in the journal Theriogenology.
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