Heat stress has lasting effects on dairy cows

Two years after birth, cows from heat-stressed cattle produce less milk.

If lactating dairy cattle get too hot, they don’t produce as much milk, and that can add up to economic losses of more than $1 billion a year in the U.S. alone, according to University of Florida researchers.

This loss easily can double if dry cows — those in late pregnancy that are not lactating — suffer from heat stress. That stress causes cows to produce less milk during their next lactation and also affects the growing fetus, said Jimena Laporta, an assistant professor of animal sciences at the University of Florida Institute of Food & Agricultural Sciences (IFAS).

So, it’s just as important to keep the pregnant dry cows cool during hot months, Laporta said.

A new IFAS study found that, two years after birth, cows born from heat-stressed mothers produced less milk. The research delves into why dairy calves that experience heat stress in the womb, particularly during the last trimester, produce less milk later.

IFAS researchers looked at the mammary glands from cows that were born from heat-stressed mothers and found that excessive heat in the womb limited the optimal growth and development of those glands, according to an announcement from the university. This exposure to heat stress in the uterus likely leads to less dairy production in adulthood, Laporta said.

However, if pregnant dry cows go through systems that relieve the heat — such as shade, fans and water soakers — the mammary glands of their offspring are normal. Thus, by cooling a pregnant dry cow, dairy farmers can avoid lower milk production of the cow in her next lactation and her offspring two years later, Laporta said.

For the past eight years, IFAS researchers have shown that when pregnant cows are exposed to too much heat before they calve, they produce less milk in their next lactation.

“Now, we know that heat exposure in the womb compromises normal mammary gland development and reduces the milk production of their offspring two years later,” Laporta said.

“This research can have a significant impact for the dairy industry, particularly in Florida and the Southeast, which experience more than 200 days of hot weather annually,” she said.

The study, led by Laporta and IFAS animal sciences professor Geoffrey Dahl, was published in the journal PLOS ONE.