This is my first horse and he is an Appendix (thoroughbred/quarter horse cross). He has a long slim athletic build much like a thoroughbred. I came out to feed him this morning and he was shivering horribly. I stalled him for the morning to dry off by I have questions. I've decided to put him on grain to add some weight to him since his skinny build doesn't seem to provide much warmth. I bought him a blanket but when is it appropriate to take it off/keep it on? Should I stall him at night and turn him out for the day as the temp drops? And what grain do you suggest?
Shivering is a way to protect an animal from the cold. It generates heat. This is fine when you have a horse that is nicely rounded from plentiful feed over the warmer months, as shivering uses energy and use up fat stores. If a horse is underweight they are likely to feel the cold more, plus have less reserves to combat that old through shivering.
The best source of feed to help a horse cope with the cold is roughage. Pasture (which is often in less supply over winter) or hay are good ways to fee roughage. Ensuring your horse has a plentiful supply of hay is the first thing to consider. This combined with a hard feed regime if they're struggling to keep weight on may be necessary. Grain alone is not a good idea. It can cause hind gut acidosis, plus rev the horse up. Large amounts of grain can be eaten quickly and get pushed through the gut without being adequately digested. Abundant roughage helps prevent this. The horse will be more prone to ulcers also. As horses need feed in their stomachs around the clock to prevent acid from hitting the top of the stomach.
If the horse is thin or doesn't have shelter, then rugging may be necessary. Older and very young horses may also have different rugging requirements to fit healthy adult horses. The issue with rugging, is overheating can cause dire health problems for horses. So horses left with rugs on during the day, if the temperature rises and there's no shade (even with shade) can cause a problem for the horse. If the temperature is rising during the day and you cannot take the rug off in the morning and put it back on at night, it may be preferable to leave rugs off altogether.
There's various research on the temperatures to mind when rugging horses. Note, these are not hard and fast rules, there's considerations, such as rain, snow, wind, shelter, horse condition and health. If it drops below 5 degrees C overnight, pop a rug on. If it's getting to 15 degrees or higher during the day, take it off. Horses need sunlight, even during winter they absorb the sunlight into their skin through their winter coats, so it's a good idea to try and avail horses some rug free time during the day. I have an old horse, if the temperature drops to 11 degrees C overnight or lower, I rug her. She's 27 and has trouble keeping weight on.
Be mindful of the rug heaviness/thickness and whether it's waterproof. Canvas rugs are preferred by many horse owners, as they are breathable. Synthetics are lighter weight, but horses are also more likely to sweat and not get relief from the damp caused by sweat under a synthetic rug. Where we live it doesn't get below 5 degree C at night. I use a combos 200 and 100 gsm rug when it's bitter and my old mares had limited shelter and on a young foal without a mother (the other horses remained unrugged). When it wasn't so cold I used an standard rain sheet, no neck no padding to help my older girl cope with the rain and the cold. Now the nights are dropping to 14 degrees C and it's raining, I'm not so concerned, she has shelter and the days are reaching 22 degrees C. Too hot for rain sheets and winter rugging.
Pic of combo for older mare and rug for young foal without mum
Pic of rainsheet on older mare for the transition weather
Pregnant mare paired with young foal (with no mum). Mare is not rugged, foal is. Winter here.
Horses naturally stay warm by moving around. They're also social creatures and require the company of other horses. They will naturally find shelter and shelter as a group. If there is no shelter, possibly stalling overnight would be good. But ensure there is a plentiful supply of hay and fresh water. If the temperature is dropping within the stall, rug him. He cannot move around to get warm in a stall.