Cattle Heat Stress

The past week the weather has been HOT, and the forecast is calling for some very warm temperatures for the next week. These hot days can make us uncomfortable but have you thought about how your cattle feel about it?

Bos taurus cattle, the type generally used in Colorado beef production, do not tolerate heat and humidity as well as humans do. The young beef animal has a thermal comfort zone that ranges from 45 to 80°F. When you look at the thermal comfort zone for mature cows and feedlot cattle you can expect it to range from 0 to 75°F. Additionally, you must take into consideration the animal’s nutrition level, body condition, hair length and coat color; as these can all shift the animal’s comfort zone levels.

Anytime that the temperature hits 90°F you can expect that your cattle may be suffering from some level of heat stress. An increase in humidity can make this threat greater, even at more moderate temperatures. I would recommend that cattle producers acquire a Temperature Humidity Index (THI) table and use it as a heat stress monitoring tool. You can use this table to compare temperature and humidity to see what combinations are dangerous and critical. Whenever a THI value on the table indicates 79 or higher, extra diligence in observing the condition of your cattle is warranted.

When temperature and/or humidity begin to rise, monitor your cattle for signs of heat stress. These animals may move about looking for a more comfortable area. Additionally, they may begin to slobber and have a respiration rate of more than 100 breaths per minute. Often times heat stressed cattle will hold their head high in an effort to breathe easier and stand facing into the sun, limiting the amount of solar radiation that hits their body. Another important heat stress factor is the low temperature for the 24-hour period. Cattle rely on a cool down at night to be able to remove heat from their bodies. A six hour period below 70°F is needed to regulate body temperature following a critical heat stress day.

Cattle that are suffering from heat stress may consume two to three gallons of water for every 100 pounds of body weight. These large amounts of water allow cattle to sweat and urinate more than usual. This is considered to be the quickest and most efficient way that cattle have to cool themselves. The increased water need may require that the manager provides additional water tanks. Research conducted with feedlot animals has suggested that providing an additional three linear inches of water space per animal can be a lifesaving management practice during a heat wave. As always, make sure that the water is clean. During a period of heat stress you do not want to take any chances that cattle will refuse water.

Other important management practices to consider during critical periods of heat stress are airflow manipulation, shifting of schedules (early am cattle handling and late evening feedings), and possibly even building shade and providing a water mist, in extreme situations.