Cattle Plus Extreme Heat Equals A Bad Combination

JOHNNY MORGAN

BATON ROUGE, LOUISIANA

This summer’s extreme heat has been and continues to be brutal on Louisiana cattle.

When the temperature at night remains above 80 degrees, it’s really hard for cattle to cool down.

During an average year, August is the worst month for heat stress in cattle. But this year, high temperatures arrived early in June.

LSU AgCenter veterinarian Dr. Christine Navarre said this summer has been especially bad.

“Extreme heat exposure day after day for months on end is debilitating to production and the health of cattle,” she said.

According to Navarre, with these scorching temperatures, poor forage quality from the drought adds to the problem.

“Poor quality forage is harder for them to digest, which causes an even higher body temperature,” she said.

Cattle can dissipate heat in only four ways: radiation, convection, conduction and evaporation.

“The first three mechanisms only work if air temperature is less than their body temperature,” she said. “During summer, when air temperatures are either approaching or above body temperature, evaporation through sweating and respiration is the only mechanism left. And at high humidity, evaporative cooling decreases.”

There is not a lot that can be done. But two things are mandatory: fresh, clean water and shade.

“It’s also very important to provide water close to the shade since they may not leave the shade to drink and will actually die of dehydration,” she said.

Heat stress affects some animals differently. In mature cattle, the biggest negative influence is likely on body condition and reproduction.

With calves, heat stress leads to decreased weight gain from a combination of decreased dry matter intake and decreased milk yield in dams.

“Heat stress-induced infertility in bulls can be permanent, so breeding soundness exams each year on breeding males is essential to make sure they have recovered,” Navarre said.

Genetic selection of heat-tolerant cattle is also important.

“Bos indicus cattle, like Brahmans, are more heat tolerant than Bos taurus breeds because they have more sweat glands, lots of loose skin and their sweat glands are larger,” she said. “Body temperature starts to increase in Bos taurus cattle between 70 and 79 degrees and in Bos indicus cattle at 90 degrees.”

If Bos indicus genetics do not fit your business model, then consider selecting Bos taurus cattle from herds that have been developed over several years in the South, Navarre said.

Navarre added that it is better to have light-colored cattle in extreme heat because black-hided cattle absorb more solar radiation and have a harder time managing the heat load. ∆

JOHNNY MORGAN: LSU AgCenter