As the mercury rises and summer swings to full tilt, now’s a good time to think about how ambient heat and humidity can affect the health of our farm animals. Let’s review the signs of heat stress in livestock.
Because the rumen in cattle, sheep and goats is a giant fermentation vat, it generates a lot of heat. Acting as an innate furnace, this is an obvious advantage in the winter but can be a burden in the summer.
For this reason, ruminant livestock (especially cattle) can experience even mild heat stress in temperatures that humans would consider relatively comfortable–upper 70s and 80s F. An additional factor is that cattle do not sweat as much as humans do and lack other means to shed excess body heat.
As humidity increases, this makes things worse.
Researchers with the USDA’s Agricultural Research Service (ARS) have determined that respiratory rate is a good indicator of the level of heat index cattle are experiencing. Normal bovine respiratory rates should typically be under 90 breaths per minute (bpm). Breathing rates above this signify:
- alert for heat stress (90 to 110 bpm)
- danger of heat stress (110 to 130 bpm)
- an emergency situation (above 130 bpm).
This is a very handy method to quickly assess your animals.
Other clinical signs of heat stress in ruminants include:
- changes in behavior, such as agitation and reluctance to lay down
- foaming at the mouth
- open-mouth breathing (extreme situations)
More chronic indications of heat stress in a livestock herd include decreased weight gain due to decreased dry matter intake, decreased milk production and shorter gestation lengths in pregnant animals.
Horses and other equines have a much better aptitude for sweating as compared to their ruminant counterparts. However, as humidity increases, the effectiveness of sweat in cooling the body decreases until becoming mostly ineffectual in extreme heat and humidity (e.g., 95 degrees F and 90 percent humidity).
If horses cannot cool down rapidly in such conditions, their large muscles quickly overheat.
A horse in heat stress will have an increased respiratory rate, like ruminants, and paradoxically may actually have dry skin. Mucous membranes will also be dry and the horse may exhibit neurological signs such as stumbling and weakness. This can quickly devolve into seizures and severe physical harm and death if veterinary care is not initiated immediately.
Pigs are particularly prone to heat stress due to their short statures, large muscles and thick subcutaneous fat. They also lack the ability to sweat and instead utilize panting to dissipate heat like a dog does. However, panting can only help so much. Overheated pigs, like other livestock, will not eat as much or stop eating altogether.
As heat stress continues, they will open-mouth breathe and you may see red splotches on light skinned pigs. Over-heated pigs may begin to vocalize more than normal and become stiff-legged or develop muscle tremors and not want to move at all.
So what should farmers do for their animals in the summer? Providing adequate shade is a huge help, as is the obvious: provide plenty of clean, fresh water.
Another rule is to avoid working animals—that means don’t excessively ride horses, don’t vaccinate cattle, don’t castrate lambs, don’t shear alpacas—in high heat and humidity. If you must process animals, try to do so in the early morning or in a location with shade and ample air circulation.