Summer heat and humidity can cause stress on your calves, leading to pneumonia. Healthy cattle can handle some heat stress but too much heat along with high humidity can result in excessive stress and can even lead to death.  The increased respiratory rate along with the stress of heat can overwhelm the natural defense system.  Dr. Karl Hoppe from North Dakota State says in Beef Magazine that once cattle start to pant, you know heat stress has already occurred.  Cattle can get some relief from the stress if the nighttime temperature falls below 72°F, which may happen in North Dakota but usually does not happen in much of the Texas summer. 

If calves did not get adequate colostrum when first born, the risk is even greater.  Calves with pneumonia can be recognized by rapid respiration, lethargy, drooped ears, and a dam with a full udder.  Adult cattle and yearlings can also develop heat stress pneumonia, especially if they had some respiratory issues as calves, and may already have scarring in their lungs.  You may find calves that appear to be having a really difficult time breathing, all of a sudden, on the first really hot and humid day, and this may be because their lungs were damaged early in life but it was undetectable until they were stressed.  Usually, healthy cattle do not die from heat stress initially but after a few days, some cattle can’t handle the stress and cumulative days without night cooling make it very difficult on these individuals. 

Cattle are at danger from heat exposure when:

• the heat index is 75°F or greater for three consecutive days
• the heat index during a 48-hour period is not lower that 79°F during the day and 75°F at night
• the daytime heat index reaches 84°F or higher for two consecutive days, all of which are common in Texas summers.