Heat stress is hard on livestock, especially if it is in combination with high humidity and low wind speed. The degree of heat stress is dependent on the animal’s activity, body condition, coat cover and color, and disposition.
Signs of heat stress (depends on specie) may include animals bunching, seeking shade, panting, slobbering or excessive salvation, foam around the mouth, open mouth breathing, lack of coordination, and trembling. If these symptoms are observed, assume the animal has a heat load. Immediately try to minimize the stress to the animal, especially handling or movement of the animal. Previous health of individual animals is an important risk factor; animals that have had past health problems will be more affected by heat stress than animals with no prior health problems. These animals will generally be the first to exhibit signs of heat stress and be the most severely affected.
Effects of heat stress
Hot weather and high humidity can reduce feed intake, weight gain, reproductive efficiency, milk production; while increasing susceptibility to disease. Changes in behavior and even death can also occur.
The comfort zone for animals varies depending on age. Young animals generally have a narrow comfort zone between 45 degrees F and 80 degrees F; while the range in temperatures of the comfort zone of mature animals can be wider. For example, feedlot animals and mature cows the comfort zone can range from below zero in the winter to about 75 degrees F in the summer. Bos indicus cattle do have better heat coping capabilities and can easily tolerate temperatures above 90 degrees F.
What is a heat index?
Environmental stress is dependent on temperature, humidity, wind speed, and solar radiation; which is best determined by an index. The index that is most commonly used is called the Heat Index, which is commonly reported by many media outlets during the summer. This index, which is used for humans, has a threshold that is very close to the livestock temperature-humidity index.
The following guidelines should be followed for show animals:
Heat index above 100: still stressful for the animal, but they will be able to tolerate it if shade is available and/or wind speed is at least 10 mph. Thus show animals should be provided shade and/or moving air via fans.
Heat index above 110: stressful for the animal regardless of wind speed. Show animals should be in the shade with fans, especially market ready animals, and have plenty of access to water. If a heat index above 110 is predicted, livestock shows should be completed by noon. In addition, livestock that need to be moved or transported should be out of the facilities by early morning but certainly by noon, if possible.