I have an Arab mare that, while fat and furry, tends to need a blanket when temps REALLY dip low. I had never blanketed any of my horses before her, but the first winter I had her I came out one morning and she was shivering, and that was it.
I have had winters that were so brutal she wore the blanket almost all the time, and I have winters so mild she only had it on a few times. The problem is that short of seeing her shivering, I don't have a good idea of precisely when to throw the blanket on. I don't want to wait until she gets that cold, but she also needs to shed some pounds and I don't want to baby her through the winter either.
What criteria do you use to determine when to blanket your unclipped horses? Do you just throw it in if you are unsure and check them regularly to make sure they aren't too warm?
My TB mare also, while she does grow a decent coat, really can't handle the cold. She will shiver and she's a hard keeper already, so I don't want her to have to burn energy to keep warm.
I have a medium weight blanket for her that gets the job done most of the winter. I usually put it on her at 35 if she will be out overnight. If she's in, then I wait until 30-25. The medium weight keeps her warm unless it drops below 15. I have a heavier one for those rare days, but she rarely wears it more than once or twice a year.
I picked 35 by trial and error. That seems to be the temperature where she is toasty under the blanket but not sweaty.
Strong promoter of READING the entire post before responding.
I was taught by someone who is expert in these things to feel the base of the ear. The horses ear acts as a mini radiator and if the horse is cold, will slow blood to it to save heat for the rest. Has worked for me as a reliable indicator of temperature for 18 years.