I get a lot of questions about blanketing horses because there are a lot of opinions out there! Here is my take on it. Some people will agree with me, and some won't, and that's ok :)
My boiled-down opinion on blankets: they are annoying and expensive. You have to find ones that fit right, store them (and find them after you stashed them somewhere), clean them, and repair them. When the horse is wearing them, you need to check them all the time and make sure the horse isn't wet underneath, getting rub sores, or infections. And if you are a blanket long-hauler (all winter) you need to be checking the horse's weight gains or losses because you won't see it.
My boiled-down opinion on horses: they are tough. Most of the time they don't seem to care about the cold. Even when they have a shelter (you can see my south-facing shelter in this picture) my horses are very seldom inside in winter. They like being outside where the herd and the hay is (my hay is where I am standing taking this picture). They have an amazing ability to maintain their temperature when they are healthy and in good weight.
So, you can see where I am going with this. For most horses most of the time, I don't think the effort and cost of the blanket is worth it. However, I do maintain a blanket for each of my horses ready to go because of extenuating circumstances:
-Last year (2021) it was the polar vortex in February (remember how nasty that was, and if I recall correctly, it went on for a couple weeks!). Dixie had started shivering violently one night so I blanketed them all. I will add that the blankets I have are all waterproof and the very puffy kind. If I were to put on a thin style blanket not rated for really cold conditions, it would just flatten their own natural haircoats rendering their own insulation useless. If the blanket isn't waterproof and collects snow, you really have to watch that the horse isn't just wearing a wet blanket which defeats the purpose obviously.
-Individual horses present different needs. I have owned Dixie for quite a while. She never grows much of a winter coat and like I mentioned, last year I saw her shiver for the first time. It might be age-related; she is my oldest horse at 19yr. Last night (1/5/22) when I went out late to do chores in 10ish degrees, she was shivering. I would call shivering an extenuating circumstance. She's older, pregnant, and not the easiest horse to keep weight on. I was very happy I had a blanket ready to put on her because I sure didn't want her shivering all night. Yes, she would survive and would probably acclimate to the new colder conditions, but I knew the next couple days were going to be even worse. She already has all the hay and equine senior pellets she wants so feeding extra isn't applicable. She has shelter but she would never leave the herd to go in there by herself and she does not like being locked in. I don't want her diverting her energy to stay warm, I don't want her immune system suppressed with that baby in there, and there's no reason for her to be miserable. A blanket is an easy solution.
Dixie is not "being dramatic" or "being a baby." She's not trying to manipulate me and blanketing her isn't "spoiling her." I say these things because I have seen people's attitudes toward blanketing lean toward some kind of pride about NOT blanketing, as if there is some award to be won by making your horses tough out the conditions without help. I think there are some people who take pride in their horses' toughness--even bragging about it--as if it makes the OWNER somehow tougher and more impressive. What's funny is I've had conversations like this while the owners are in full Carhartt winter gear, nice boots and gloves, etc. You really can't consider yourself tough unless you take all off all the extra layers and shiver violently to build your character and resilience! Then I will be very impressed! Seriously, I've been-there-done-that a couple times camping in some nasty cold weather--no thanks! If our horses are hungry, we feed them. If they are in pain, we find the problem and treat it. I don't understand why blanketing or sheltering a clearly cold horse that is not acclimating well for whatever reason is somehow "spoiling them." By all means help them out!
I'll also tell you the reasons why Dodge, Eli, and Stella aren't blanketed. None of them have shivered or acted stressed by the cold. If they did, I would blanket them of course (each has a blanket ready if needed). Stella has a thick winter haircoat and takes good care of herself. She is kind of a loner and she will gladly leave the others to go to the barn to warm up in the sun, and if I put fresh bedding down in the barn she goes in there to sleep at night instead of sleeping on frozen ground. Dodge hardly has a winter coat (like his mother, Dixie) but he has never shivered. He is an easy keeper and that helps because he has some good fat for insulation and if he used a bit more energy to keep himself warm, I wouldn't notice any weight loss. Eli has a lot of hair and he's just huge which seems to help. He is also an easy keeper, eats a ton, and gets by just fine. Dodge and Eli are like little kids that are always together but bug each other. Eli is new to me and I haven't blanketed him yet, but I think if I did, Dodge and Eli would chew on each other's blankets and cause trouble!
-My horses do tend to go inside the barn during cold rain. If they didn't have the ability to escape cold rain or sleet, I would definitely blanket.
-Some people keep their horses blanketed all winter to reduce the winter haircoat growth so they can keep up their exercise routine. This is a nice thing to do; I can't imagine running on the treadmill with a winter coat on! I know the prevailing thought out there is that it's the short days/long nights that promote the winter haircoat growth as opposed to temperature, but it sure seems like they grow less winter hair when they have a blanket on. This point gets argued a lot so maybe there is some horse-to-horse variation on this. Also, some horses should be blanketed all winter because they need to gain weight. If they don't have to work as hard to stay warm, they can put weight on faster. Blind horses don't always get good winter haircoats either because they don't detect the short days.
-Other extenuating circumstances are injuries and illness. I see this all the time where a poor horse is suffering, laying on the cold ground due to illness or injury, and no one has a blanket to offer it. Or the horse would and should lay down but doesn't want to because the ground is so cold. Or you need to haul the horse in an emergency situation and the trailer has open air and it's zero degrees or less. Even if your horse doesn't normally need a blanket, you need to have one ready because these things frequently happen at night, weekends, and holidays--as you know! Don't count on buying or borrowing one; you need to have one ready just in case.
-Donkeys are not cold-tolerant like horses are. I could write a lot about this although I don't have all the answers. Some get through winter fine, but others really suffer and get hypothermic and worse. You really need to watch your donkeys closely. Take any shivering or cold-intolerance symptoms seriously and provide shelter and blankets right away. While a cold horse will still be standing there the next morning, the donkey might not be. I've seen some weird manifestations of hypothermia in donkeys and if it happens it is really hard to bring them back.
In summary, have the right kind of blanket on hand in case you need it in a pinch. If your horse is showing signs of trouble with the cold, put it on! If you're a big blanketer, don't be too hard on the rest of us minimalists; our horses will be okay. If you want your horse blanketed all winter to be kind to them, go for it but keep a close eye on it. If you're vehemently opposed to blankets, be open-minded that there are circumstances and horses that need them. As I write this in my warm living room, I'm wearing baselayer pants, insulated Firehose pants, two shirts, a Carhartt vest, and wool socks. We all do enjoy being warm, don't we?