August 15, 2017

Cows conceived under cooler temperature produces more milk

A new study conducted by US researchers has found that heat stress undergone by conceiving cows have lifelong effects on their offspring, which have to do with the latter's milk production and quality.

The study, titled "Season of conception is associated with future survival, fertility, and milk yield of Holstein cows" and published in the August 2017 issue of the Journal of Dairy Science, studies the effects of heat stress on calves conceived during summer.

Pablo J. Pinedo, of the Colorado State University, and Albert De Vries, of the University of Florida, examined data from more than 152 herds of dairy cattle in Florida, where cows experience hot summers and mild winters. They assessed seasonal effects on pregnancy by examining more than 667,000 records from Holstein cows calving in Florida between 2000 and 2012.

Using environmental data from the US National Oceanic and Atmospheric Administration, the researchers estimated the resulting heat stress on each of the 152 herds by comparing milk yield during summer and winter months to identify which herds were most likely to suffer from heat stress during the summer.

The researchers found that milk production was greater for cows born to a mother that conceived in the winter compared with cows born to a mother that conceived in the summer. Moreover, their milk yielded greater milk fat and protein.

It was also found that the odds of survival to a second calving were 1.15 to 1.21 times greater for cows arising from a winter-time conception than a summer-time conception.

"Our results showed that cows that arose from a pregnancy conceived in winter had, on average, better survival, better reproduction, and greater milk production than cows arising from a summertime pregnancy," lead author Pinedo said. "These effects were more pronounced among first-parity cows compared with older cows."

The authors noted that although previous studies reported the effects of heat stress during late pregnancy, results from their study suggested that heat stress at the time of conception may permanently programme the genetics of the adult animal by affecting epigenetic processes within the early embryo.