Changing cow care in hot weather

By MaryBeth Matzek
MAA Editor

It is summer in the Midwest and that means hot and humid weather. Unfortunately, dairy cows do not like the heat and see their production and health decline.
The Missouri Dairy Industry Alliance (MDIA) and the University of Missouri-Extension recently held a field day to educate nearly 100 farmers on how they can make their cows more comfortable in hot weather and improve their overall health.
“Dairy cows are very vulnerable to heat stress,” said Reagan Bluel, an Extension dairy specialist. “In addition to lost milk in the lactating herd, recently released research from Florida shows that heat stress during the last 42 days of the dry period causes changes to the unborn calf with lasting impact. During parturition, the calf of a heat stressed dam is more likely to be delivered stillborn. Additionally, she is born about 10 pounds lighter and is more likely to be culled during the first year of life.”

To combat heat stress, Bluel said there are several steps farmers can take including:

  •  Increasing water intake for all animals. Make sure it is plentiful and clean.
  •  Cooling dry cows since developing fetuses are affected by heat stress
  • Changing nutrition and rations as temperatures increase. As it gets warmer, cows tend to eat less and prefer feed wet in nature.
  • Improving air movement inside holding pens via fans
  • Adding sprinklers to pens

Bluel said heat can cause milk production to drop 20 percent. She said farmers not only need to figure in the heat temperature, but also humidity levels. Combining the two creates a Temperature Humidity Index or THI. A cow begins to experience heat stress once THI hits 68.
In addition to decreased milk production, Bluel said farmers need to also think about heat affects fetal health.
“These calves born to summer-heat-stressed dams that make it to breeding, experience compensatory gains and will catch up with the cooled-control calves as a bred heifer. So, at a glance, body weight and condition would appear the same,” she said. “However, once they calve there is an immediate difference in milk production. The Florida researchers followed this group of animals for 35 weeks and saw an 11-pound/cow/day difference in milk production.”
MDIA is nearly two years old and the heat-stress educational session was the group’s third event. Chairman Sean Cornelius said partnering with the University of Missouri Extension to educate farmers has been successful.
While heat stress was the focus of this year’s sessions, Cornelius said, “last year’s events concentrated on reproductive strategies and milk quality issues respectively and were held at the University of Missouri Foremost dairy farm. Going right to the dairy farm for interactive learning is something dairy farmers enjoy and let them see successful strategies for managing their cows.”
Cornelius said MDIA will offer another learning opportunity this year for farmers.