All animals have a surrounding temperature that is the most comfortable for them to live in; for adult cattle their thermoneutral zone ranges from 45-55°F. When an animal is above their thermoneutral zone, stored body energy must be released to try and dissipate heat. The hotter the animal gets, the more energy used to try and stay near their thermoneutral zone.
Cows naturally generate and absorb heat from digestion, milk production, and their environment. Heat stress occurs when cows generate and absorb more heat than they can easily get rid of through respiration, sweating, and from air ventilation. Heat stress leads to increased respiration rates, body temperatures, and sweating which in turn can lead to reduced breeding efficiency, low milk production, decreased feed intake, lower weight gains, and an increased chance of sickness as the immune system requires a lot of energy to function properly.
High temperatures can cause great concern when working cattle, especially when paired with high humidity; in combination, these can strongly increase the risk of heat stress in cattle. Cows experience heat stress at much lower temperatures than humans. In general, mild heat stress starts around 72°F with 50% humidity although the hide color can affect the amount of heat stress cattle can go through; black hided cattle’s surface temperature can be 10-15°F warmer on average than white or red cattle.
Respiration rates and body temperature are both good ways to monitor how your herd is managing their heat production. If more than 5-10% of cows have an elevated body temperature or increased respiration rate, it is considered an emergency and immediate action should be taken.
|Heat stress level||Temperature humidity index (THI)||Respiration (breaths per minute)||Body temperature (degrees Fahrenheit)|
|No heat stress||Less than 68||40-60||101.5-102.5|
|Mild to moderate||72-79||75-85||103-104|
|Moderate to severe||80-90||85-100||104-105|
Cattle’s core temperature peaks 2 hours after the peak environmental temperature and takes at least 6 hours to dissipate their heat load. Meaning, if peak temperature occurred at 4 PM, cattle will not have recovered from that heat load until after 12 AM and it will be even longer before cattle have fully recovered for the entire days heat load. For this reason cattle should not be worked in the evenings, even if it has cooled off a little. When working your herd pay close attention to the forecast, if possible work early in the mornings to help reduce the risk of heat stress. Providing a source of shade such as trees, buildings, or sunshades as well as improved ventilation with fans or windows and a constant water supply are some easy management options that can be implemented, as well as an adequate source of cool, clean drinking water. (Increased water temperature can more than double total water requirements for your cattle.)
Be smart when working your herd – if you are hot, your cattle are even hotter.
-Work in the morning
-Provide shade and or ventilation
-Have a water source available
These are some of the easiest ways to combat and hopefully prevent heat stress in your cattle. If you begin to notice any of these signs or symptoms, halt and contact your local veterinarian if symptoms persist.