The lazy days of summer may mean pools, hammocks and lemonade to some, but to horse people it means sweat, more sweat and even more sweat. Working and competing in the heat can be difficult and at times downright dangerous to both horses and humans.
Under harsh conditions it is important to pay attention to your own body as well as your horse’s, so that neither one becomes ill. And even though we are different creatures, horses and humans both have the same basic physiological responses to extreme heat. Children, the elderly and unfit people are most susceptible to extreme heat, as are horses that are sick, geriatric, unfit or heavy-coated.
When We Heat Up
When the seasons shift from winter to spring and then summer, the horse acclimates by increasing blood flow to the skin, decreasing fat layers and shedding the hair coat. Acclimating from cold to warm takes time, depending on the horse’s (and your) workload and fitness level. During exercise, energy is produced by muscle metabolism, and about 80 percent of that energy is released as heat. In hot weather, the horse’s thermoregulatory system must transfer that heat to the environment to prevent excess accumulation. The faster and harder a horse works, the more heat is produced. When the temperature is really high, the horse isn’t fit or is working extremely hard, the horse can’t release enough heat and becomes overloaded. In the most serious cases, it can cause collapse and heat stroke due to lack of oxygen to the brain.
Sweat is the primary means of cooling both horse and human. In extremely hot weather or under intense exercise, the horse needs to expand blood volume to accommodate sweating. In a dry, hot environment, evaporative cooling is good, but you can dehydrate very quickly. On the other hand, high heat and humidity cause slowed heat loss because the air is already saturated with water. Sweating is therefore less effective. Once dehydrated, a horse or person overheats faster than a hydrated one, because less fluid is available for sweating and the body is not able to move heat to the skin surface as well.
When Trouble Occurs
Lethargy, rapid pulse, heavy breathing and a temperature over 105° F are signs that a horse is in trouble. Here is another situation where knowing what is normal for you and your horse will tell you a lot about the situation.
Generally speaking, in people aged 11 and up, the resting heart rate is 60 to 100 beats per minute (BPM), or 40 to 60 BPM in a well-conditioned athlete. The normal respiration rate is 12 to 24 breaths per minute and normal temperature is 98.6° F.
In horses, the resting heart rate is 35 to 45 BPM. It could go up to 80 to 100 BPM immediately following exercise, but within 15 minutes, it should be 40 to 50 BPM. Resting respiration rate is 10 to 20 breaths per minute. A hot horse will breathe rapidly, but that isn’t a bad thing. A high respiration rate of 120 to 140 breaths per minute improves evaporative heat loss through the respiratory tract. However, it should drop to 60 to 80 breaths per minute after the first 10 minutes. Rectal temperature in the horse is typically 99.5° to 101.5°. It is not unusual to see a horse’s temp go up to 104° or 105° in very hot weather. However, it should come down within 10 to 20 minutes after exercise. If it stays above 105°, heat stress is a definite concern.