Some horses might struggle to maintain a healthy weight in very hot and humid weather. | iStockQ: Last summer we had a run of very hot temperatures, and my pleasure horse lost weight. I want to be proactive this year and maintain his weight, as well as minimize the risk of heat stress. What changes should I incorporate into his diet as summer approaches?A: Similar to cold weather, high temperatures and humidity make a horse expend extra energy to maintain his core body temperature. A horses thermoneutral zone, which is the ambient temperature range he can maintain his normal body temperature using metabolic regulation, is 41-77 F. In comparison, a humans thermoneutral zone range is 77-86 F. Besides air temperature, factors such as humidity, wind velocity, solar radiation, and precipitation can also affect a horses ability to thermoregulate.Unlike in winter months, nutritionists do not recommend increasing the horses summer forage intake because the cecum produces heat when it digests and ferments forages. Winter conditions make this helpful in the winter, when the horse needs to stay warm, but it interferes with cooling in the summer. Avoid legume forages, such as alfalfa and clover, and feeds high in protein because the process of digesting protein also produces heat. Your horse also needs to drink more water with these forages to flush excess nitrogen out of the system.Adding Fat to Your Horses Diet During SummerWhen a horse needs more calories without added feed volume or heat-producing ingredients, consider what youre feeding. Fats can meet these criteria. Fat supplementation offers several advantages for helping a horse maintain weight in the summer months. These calorie-dense products, which are highly digestible, dont result in excessive heat produced during digestion. Pound for pound, fats provide more than twice the calories of soluble carbs, allowing your horse to get more energy from a smaller amount of feed. Fats, especially from vegetable sources, tend to be palatable, and most horses consume them readily.If your horse is already on a commercial feed mix, you might be able to switch to one higher in fat. There are many commercial feeds available with 10-15% fat. You might also consider buying a high-fat supplement, such as rice bran, to increase calorie intake. Nutritionists recommended horses eat no more than two cups of oil per day. Make feed adjustments gradually, over about a two-week period, to give the body time to adjust. If your horse develops diarrhea or steatorrhea (gray, greasy fecal balls), reduce the amount of fat until feces appear normal. Monitor the feed, supplement, or oil for signs of it going rancid. Storing in a cool environment can help you avoid this.Horse Water Consumption During SummerMonitor your horses water intake closely, especially during summer months. Horses consume more than the average one gallon per 100 pounds of body weight when temperatures rise. Because sweating is the most efficient way for a horse to cool the body, they need to drink more water to replace water lost through sweat. In addition to water, horses also lose electrolytes when they sweat. Be sure your horse always has access to salt and consider adding additional electrolytes to the diet. Consult an equine nutritionist if you need help choosing an electrolyte supplement.Take-Home MessageTo help your horse maintain a healthy weight during summer, be sure he has access to cool water and to salt at all times. Avoid feeds containing excess protein and consider switching to a high-fat feed. Alternately, you could add a fat supplement to his current diet to introduce more calories without adding bulk to the meal.Do you have an equine nutrition question? Do you have an equine nutrition question? The Horses editors want to hear from you! Submit your question via the form below. Name(Required) First Last Email(Required) Submit your equine nutrition below!(Required)CAPTCHA