Watch cattle closely as high heat continues

News
Jun 29, 2012

The heat situation for cattle continues to reach into the ‘danger’ and ‘emergency’ areas, according to USDA’s Meat Animal Research Center. The estimates of heat stress are based on four specific weather factors: temperature, wind speed, humidity, and solar radiation.

“Compared to other animals, cattle rely on respiration more than sweating to cool down. Wind and cool nights can help, but when temperatures are this high, producers must also consider other ways to keep their livestock comfortable,” said Matt Deppe, CEO for the Iowa Cattlemen’s Association.

Iowa State University’s Extension beef veterinarian, Dr. Grant Dewell, recommends these protective measures:

• Clean, fresh water—consumption of water can double during heat events. Cattle need at least 2 gal./100 lbs/day during heat events. Additionally, make sure there is adequate room for cattle to drink and that supply lines can provide water fast enough.

• Shift to feeding a higher percentage of feed in the afternoon and consider lowering the energy content by 5 percent.

• Provide shade if possible. UV radiation is many times the critical factor for livestock losses due to heat stress.

• If necessary, begin sprinkling cattle with water if signs of heat stress are evident.

Deppe says producers who start using fans or providing water sprinklers on their cattle should be prepared to use that process until more moderate temperatures return.

Feedlots need to monitor environmental temperatures throughout the summer. Any time the Temperature-Humidity Index (THI) is above 80, cattle will be under heat stress. Hot weather following precipitation can increase the THI dramatically. Deppe says if overnight temperatures are above 70°F, cattle will have increased heat stress. Several factors influence heat stress in cattle, including:

• Genetic components including breed, temperament, and color can play a part in heat stress. Breeds, breed crosses, or composite breeds from cattle with historical origins in the tropics or subtropics tend to be more heat tolerant relative to those cattle of 100 percent European origin.

• Color plays an important role in heat tolerance. Dark colors absorb more heat than light colors. As a result, a black animal will be more susceptible to heat stress than a white or tan animal.

• It has recently been shown that temperament also plays a small role in heat tolerance. Animals that are calmer are more heat tolerant than animals that are more excitable.

The current general health of the animal will influence its ability to withstand additional stress, including heat stress. The effects of pneumonia are long lasting. An animal that has been treated for pneumonia at any time in its past has a higher risk of heat stress symptoms during hot weather than those animals that have not had the disease. Animals which have had pneumonia and have not been treated could be at even higher risk.

Finished cattle that are ready to go to market, cattle in poor condition, and cattle that have recently arrived at the feedlot are among the most vulnerable.

Cattle that have not been preconditioned to hot weather will have a greater stress response (higher breathing rate, higher body temperature). Cattle become preconditioned to heat stress when they have prior exposure to hot weather. Moving cattle from a cool region of the country to a hot environment can increase the animal’s susceptibility to heat stress.

According to USDA reports, in the last 10 years, there have been several heat events in the Midwest; direct and indirect financial losses for these events are estimated at over $75 million for the cattle industry alone.

Cattle producers can monitor the forecasted heat stress index and find tips for cooling cattle at http://www.ars.usda.gov/ Main/docs.htm?docid=21306. More information on preventing heat stress in cattle is available at http://vetmed.iastate.edu/.

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