Equine winter hair coats 101
Most Michigan horses will grow a sufficient winter coat.
There is no question that most horses have the capacity to grow a winter hair coat that will keep them sufficiently warm in the coldest weather (at least that we’re likely to experience in the Midwestern U.S.). Winter hair growth is triggered primarily by the change in photoperiod or day length, and the winter coat starts to enter in mid to late August. While the process is directed by the change in daylight, external temperatures will also play somewhat of a role, in that a horse that is blanketed early will not develop as thick a coat. If a horse is blanketed in the fall to maintain a slick hair coat for fall and winter shows, the winter hair that grows in will be shorter than it would be if the horse were left unblanketed.
Once a horse’s winter hair coat is in place, the body heat will be trapped by the hair as it “fluffs up” providing warmth. Most horses can withstand even the coldest, snowiest weather without additional protection, provided there is shelter from rain and wind. A wet, flat hair coat will lessen the ability of the hair to “fluff”, thus lessening a horse’s ability to stay warm, resulting in more energy used to try to regulate body temperature. This energy will either come from nutritional sources, or directly from body stores, resulting in weight loss if added feed is not provided.
Forages (hay) or other fiber sources actually produce additional heat when digested by the horse and hence are the best feeds to increase in cold weather. Regardless of the price or shortage of feed, horses require 1-2 percent of their body weight in forage for optimum health. Given the use of nutritional reserves for temperature regulation, there are some horses that have the potential to benefit from blanketing, including geriatric, sick, very young, or very thin horses, or horses that are moved to cold climates before they have fully developed an appropriate winter coat for conditions.