Will blanketing early stop my horse growing a winter coat?

The best study we found on blanketed horses saw only a small difference in neck hair length in two of the winter months, and no difference in how thick the hairs were. That is a long way from a horse who never grows a coat.

It is not nothing, though, and there is a catch: a blanket can flatten the coat and take away some of its insulation, so a horse who starts wearing one is usually in it for the season. This page walks through what the research says, how much weight to put on it, and where the evidence runs out. If you are still deciding whether he needs a blanket at all, start with does my horse even need a blanket.

Rutgers Equine Science Center says horses start growing more hair in early fall as days get shorter, even when temperatures are still warm. EQUUS magazine quotes DeBoer, speaking about the blanketing study below, calling the amount of daylight the main variable that affects the horse's hair coat.

Warmth and cold still play a part. The authors of a 2020 study in PLoS One, which tested light masks and rugs on horses and ponies, say temperature, breed, housing, diet and where he is in his hair cycle also seem to matter, and call temperature an especially important modulator in ponies. Temperature was not controlled in that study, though, and the authors say so.

The practical point is that the coat is on a calendar set by the sun, and a blanket does not move the calendar.

EQUUS reports on a study from the University of Wisconsin-River Falls, published in the Journal of Equine Veterinary Science in January 2023. Eight mature, unclipped horses were blanketed from late October, and eight were left uncovered all winter. Researchers took 20 hair samples per horse each month, October through March, from the hindquarters and the neck.

The table shows what came out. DeBoer says the length difference was statistically significant only for neck hair two months of the year, and describes it as a change that may be short-lived. Hair coat growth over the winter followed a similar pattern whether or not the horse was blanketed.

Timing matters here. The blankets went on at the very end of October, when temperatures were consistently below 40°F. DeBoer suggests that starting earlier might have produced a bigger difference, but that is her hypothesis, not a result.

Rutgers says artificial light can lengthen the day to 16 hours to thin a heavy winter coat. The PLoS One study is the one that tested it: horses and ponies wore a light mask that extended their day to about 15 hours and also wore rugs. Started at the autumnal equinox in stabled animals, it had no effect, and the treated horses still grew long, thick coats. Started about one month before the winter solstice in outdoor Irish Sport Horses, treated horses ended with shorter, lighter coats and shed more, with effects only appearing weeks after the solstice. In ponies it did not reliably work in winter.

Two cautions. The groups were small, five to seven animals each, and the researchers call the findings preliminary. And the authors include the founder and a research manager of the company that makes the light masks, which the paper discloses.

Some riders see a difference from housing. This rider's experience is one horse and is not evidence, but it shows why people wonder:

Rutgers says that once you start blanketing you should expect blanket duty all season long. It also says blanketing one year does not mean you have to the next.

That is the real trade-off. If you start in September and the weather turns mild in October, the blanket may make him sweat. University of Maine warns that a blanket left on as the temperature climbs can leave a horse sweating and then shivering at night. Our too hot or too cold page shows the hand check, and what weight blanket does my horse need covers matching weight to weather.

There is also the upkeep. Rutgers says to take the blanket off at least once a week to groom and check for weight changes, skin problems and rubs. Our blanket rubs page has the fit side.

Eight blanketed horses against eight unblanketed is a small sample, and the blankets went on at the end of October, not in September or at the first cool night. Nobody has shown, in the sources we found, what a blanket does when it goes on at the equinox, or for a horse that is clipped partway through the season.

The light-mask research has its own limits: five to seven animals per group, temperature not controlled, and an unusual mix of stabled and outdoor horses. And the two studies measured different things, so they cannot be stacked into one rule.

What they do agree on is the direction. Daylight leads, and a blanket alone is not a strong lever on the coat. Beyond that, ask your vet or trainer, who knows your horse and your climate.

If he is clipped, elderly, thin or without shelter, he is a blanket candidate whatever his coat is doing, and our blanket weight calculator and horse blanket guide help you pick. If he is healthy, full-coated and sheltered, he may do fine without one.

If you blanket, plan for the season, use the hand check, and take it off weekly to look. Our blanket rubs page covers what to do if the hair starts to go at the shoulder.

Clipping removes insulation, so a clipped horse needs a blanket. Penn State lists a coat clipped for showing as a reason to blanket, and Rutgers says clipped horses need blanketing when temperatures drop. Light manipulation, per Rutgers and the PLoS One study, can thin a heavy coat, but the results depend on timing and the horse, and it is best done with your vet or trainer.

Blanketing is the route the research supports least as a way to change the coat, though some owners blanket for other reasons: keeping a horse clean, drier or more comfortable. If you are weighing it up, our page on whether he needs one is the place to begin. For a clipped horse, our blanket weight calculator gives a starting weight.

A coat that looks dull and thin while he loses weight is a vet question too, not a blanket question.

University of Maine adds that elderly horses may not grow as thick a coat as in their prime, and that horses from warmer climates may take one to two winters to adapt. Those horses are the usual blanket candidates in the extension sources. Everyone else is a judgment call that starts with the horse in front of you.