Heat stress in dairy cattle is one of the leading causes of decreased production and fertility in Nebraska dairy cattle during summer months. These losses are apparent in the decreased amount of milk shipped, increased days open and decreased breedings per conception. Some heat stress is unavoidable, but effects can be minimized if certain management practices are followed. Once the temperature goes above 80 degrees F cattle reduce feed intake, which has a negative impact on production. At 90 degrees F or above, one can usually notice a dramatic decrease in milk production ranging from 3 to 20 percent.
Humidity also plays a significant part in heat stress.
There are three temperature-humidity ranges of concern. A temperature of 100 degrees F and 20 percent humidity is the range in which you begin serious measures to ease the stress on the cattle. Some type of cooling should be started. The danger occurs as the temperature nears 100 degrees F and 50 percent humidity. The lethal range for cattle is 100 degrees F and 80 percent humidity.