Heat stress in dry cows creates problems generations later

Wednesday, August 19, 2020

Heat stress in dry cows today affects dairy herds decades later.  

Offspring of heat-stressed cows show health problems in future generations, said Reagan Bluel, University of Missouri Extension dairy field specialist.

Bluel highlights research from Jimena Laporta at the University of Florida in the third edition of Dairy Science Digest, a podcast for dairy producers. See https://extension2.missouri.edu/programs/dairy-extension.

"Research from the University of Florida helped paint a picture of the long-term impact of heat stress,” Bluel said.

When a dry cow is heat stressed, the calf inside her suffers, as well as profits. Ten years of data from the research team showed dramatic milk production losses in the offspring and the granddaughter of the heat-stressed dam. Florida researchers studied cows during their 45-day dry period. They compared the health of heat-stressed cows to those provided with shade, sprinklers/soakers and fans.

“Looking exclusively at the first generation born to the heat-stressed dam, the calf born from the heat-stressed dam averages daily milk losses of 4.8, 5.1 and 14.3 pounds over the first, second, and third lactation respectfully,” Bluel said. “The collective reduction in just milk production is more than 6,000 pounds, over three lactations. This is in addition to lower survivability rates, reduced reproductive success and increased health issues.”

Prevention matters, Bluel said, especially during the hottest part of Missouri summers.

“On average, Missouri farms experience 97 days a year when the heat could reach damaging levels,” she said. “By cooling your dry cows you’re allowing the herd to express its full genetic potential.”

Researchers found the developing heifer calf inside the heat-stressed dam was 4.1 times more likely to be stillborn, 10 pounds lighter at birth and had a lower weaning weight. Producers cull these offspring more because of comprised immunity and reduced reproductive success. 

Not only does the heat-stressed dam yield less milk, her heifer and granddaughter produce less lifetime milk five years later, Bluel said. The lasting effect can be catastrophic for the cow family.

Researchers say fetal programming is to blame for the difference in performance between the heat-stressed embryo and those that are cooled. Bluel explains that gene expression of the calf born from a heat-stressed dam changes permanently to be metabolically different from its cooled peers.

To learn more about dairy cattle heat stress effects and abatement visit dairy.missouri.edu/stress, https://extension2.missouri.edu/g3620 or https://extension2.missouri.edu/news/five-ways-to-help-cows-beat-the-summer-heat-4067.

For more information, people may contact Bluel at 417-847-3161 or BluelRJ@missouri.edu or MU Extension dairy specialist Ted Probert at probertt@missouri.edu.