Encouraging a Thick Winter Coat

A veterinarian offers advice on how to help a horse to grow enough coat to stay warm.
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A veterinarian offers advice on how to help a horse to grow enough coat to stay warm.

Q: I live in northwest Colorado, where winter temperatures can drop as low as minus 20 degrees Fahrenheit. I'm concerned about keeping my 13-year-old horse Romeo warm enough during those freezing conditions. Romeo, who is fed a senior feed, is slow at growing a winter coat, and when I put blankets on him he still shivers. What can I do to make sure that he stays warm enough?

A: This is a wonderful question because it is the opposite of what people normally ask. The hot topic in show circles is how to make that long, shaggy winter coat disappear. But how do we encourage further growth of that protective jacket that Mother Nature provides horses?

The answer lies in understanding how hair grows. It is influenced primarily by the changing levels of daylight throughout the year. In early to midsummer the hair is dormant (known technically as the telogen phase). But as the amount of daily sunlight diminishes in late summer, the horse's hair starts growing (anagen phase) until the full winter coat is in. The hair then reenters the telogen phase again until early spring, when increasing daylight triggers the new hair to grow as the old coat sheds out.

Environmental temperatures also affect this cycle. Warmer than normal temperatures slow or halt the growth of the winter coat. Other less critical but still important factors influencing hair growth include the individual's nutritional status, overall health and genetics.

The regulation of hair growth starts with sensory organs, such as the eyes, which have photoreceptors, and the skin, which has temperature sensors. These receptors tell the brain what is going on in the environment. The brain then sends out signals to the hair follicles using numerous regulating molecules to tell the hair to start or stop growing.

Now to answer your question: why Romeo appears to have trouble growing a winter coat. The first thing I would look at is his exposure to light. If he lives in a barn, make sure the lights go off when the sun sets. When people ask for help in shedding heavy coats, the answer is to keep them "under lights," which means 16 hours of light and eight of darkness. We want to do the opposite with Romeo.

Next, I'd recommend that you not blanket him too early. Also, avoid keeping him in a heated or warm barn in the late summer through early winter. If you do, the higher skin temperatures will signal the hair growth to slow or even stop. Horses generally cope with colder weather much better than we think, so resist the temptation to bundle him up. Once the winter coat has come in, you can consider blanketing on the colder days.

Senior feeds are generally very good at delivering all the necessary nutrients. But make sure that you are feeding Romeo enough. He needs to be in a good weight, with a thin layer of fat over his ribs. If he is underweight, giving him more calories will increase his body fat, which is an excellent insulator. Many people are afraid to feed a horse more than what they feel is "normal." But every horse is different and some may need a lot of feed or a high-fat diet to maintain weight. If he is an easy keeper getting only one or two pounds of senior feed per day, he may not be getting enough micronutrients to optimize hair growth. But if he gets too heavy on a standard ration, consider giving him a protein/vitamin/mineral supplement instead of the senior feed. Many feed companies make these for easy keepers or horses who get most of their calories from pasture and hay. If Romeo is getting a normal amount of senior feed, consider adding either this supplement or one of the more complete hoof supplements to his diet in case he poorly absorbs nutrients.

Given that you live in a state known for excess selenium in the soil, I would also test your horse's blood for this trace mineral. Although small amounts of selenium are essential in a horse's diet, high levels are toxic and can alter hair growth.

Finally, make sure your horse does not have any underlying health issues. Internal parasites, poor teeth, recurrent airway obstruction (heaves) and other conditions can rob a horse of the nutrients needed to give him a good hair coat. I generally do not recommend that horses be too heavy, but for those who grow poor hair coats despite our best efforts, a few extra pounds may help keep them warm for the winter. Talk to your veterinarian first to make sure there are no reasons that letting your horse get a little overweight for the winter would be bad for him.

David Trachtenberg, DVM
Ledgewood Equine Veterinary Clinic
Ontario, New York