Follow these guidelines if your horse is body-clipped. (Temperatures are Farenheit.) If he has his full coat, subtract 10 degrees from recommendation (for example, you'd put on a turnout sheet at 50 degrees, not 60). And, clipped or not, for turnout on days that are sunny and calm, dress him as if the temperature were ten degrees higher.
60-65: Turnout sheet
50-60: Sheet over lightweight liner
40-50: Midweight insulated turnout rug, or turnout sheet over stable blanket
30-40: Heavy turnout rug, midweight rug over stable sheet or fleece liner, ot turnout sheet over stable blanket plus liner
20-30: Heavy rug over fleece liner, or medium rug over quilted liner or stable blanket
Below 20: Heavy rug over quilted liner or stable blanket, or midweight rug over quilted liner or stable blanket plus fleece.
Is he chilly? Too warm? Here's how to tell.
Not warm enough: Ears cool to your touch, exposed hair coat stands on end, body tense (for instance, he stands stiffly on the crossties without cocking a leg), shivering, tail clamped.
Too warm: Restlessness, sweating under his blankets. To check, put your bare hand between the innermost layer and his coat -- and feel all the way back to his rib cage. The shoulder area near the binding, where dirt and dander accumulate first, tends to feel warm and sticky even when the rest of his body isn't.
Important: Even if temperature and conditions don't change, your horse needs you to remove and reset his blanket(s) at least once a day; twice is better. This is also your chance to check for rubs and sores that can result from even the best-fitting blanket, especially if dirt or shavings get lodged underneath. And if his blanket goes askew during the day, don't straighten it by tugging -- that hurts! Instead, undo straps and fasteners (always back to front), lift up the rear portion of the blanket(s) and fold forward to the withers, then lift completely off his back and put down again in the correct position.
These guidelines first appeared in the September 2001 issue of Practical Horseman magazine. For more on blanket design features that help your horse's blanket fit his individual conformation, see the November 2003 issue.