With proper and adequate nutrition along with appropriate shelter for protection from the elements, your goats should not need any coats to keep them warm.
Obviously, you live in a colder climate as do ,I and whether or not you are seeing it, your goats are growing a more-dense winter coat right now.
I do not think it is an expense you should need for your goats. With proper management, they should not need coats. That being said, I have a 12 year old pet goat that will likely get a coat this year. She's a very tough old lady and she hardly seems like 12 years old, but that may be due to the fact she's my first goat and gets some special treatment, lol.
One interesting thing about coats on goats is that they itch on fences and then sometimes get clipped to the fence by the clips on the coat. We had an animal with a wound that she wouldn't leave alone, so we put a coat on her to keep her away from it. We ended up replacing all of the plastic snaps on the coat with those oval things that you screw shut, so she wouldn't get stuck anymore.
I have Nigerian Dwarfs and have cheap dog coats for them, but am only using them for sub zero (F) temps. Except the one that came came from New Mexico and she just hasn't built up a thick coat like the other ones (she gets her dog coat if its expected to be under 20 F). They have a polydome.
There only are certain instances where I'd put a coat on a goat. If they just got clipped and it's suppose to be cold all of a sudden or like StonePark's goat that came from a warmer climate and isn't use to the temps at new place.
We had 58 days below zero last year, only a few others here can say that. Goats don't sweat and it is still cold and dry so moisture should not be Problem. Ours rarely go outside in the winter as they hate snow, they have a dog door so can come and go as they please.
I used a coat only for my 13 yr old herd buck. He was so old and less likely to stay warm. I, also, use coats on newborns if the weather warrants it. Otherwise, I keep very, very deep bedding in a barn that has solid partitions in a variety of places to use as wind breaks.
I think it also makes a difference on how many you have (I have 3) and if they have a relatively closed space that will capture body heat. I'm actually waiting for delivery of a 3 sided shelter. I'm going to stick the polydome in it for the winter. Right now, it's a pain for me to put all their stuff in the dome so they can eat/drink out of the weather. So the shelter will protect their food, water, baking soda and minerals but they will still have snuggle space in the polydome and more room to move about when it's snowing (I'm looking forward to putting some platforms in the shelter for climbing too).
My goats are packgoats (wethers) and sometimes we go to high country in the winter, where it gets a lot colder and the goats aren't going to be used to that. So in those cases they get their coats at night. I wouldn't put coats on goats and leave them on all the time. I think they should get used to the normal conditions where they live. But I don't see anything wrong with putting coats on them for unusually cold weather at night. They sure appreciate the warmth that the coats provide.
These goat coats are really well made and reasonably priced:
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