The natural coat is effective
Healthy unclipped horses with shelter can tolerate cold surprisingly well when dry and adequately fed.
Clipping changes insulation
A body-clipped horse may need protection sooner, especially in wind and rain.
Wet plus wind is different
Water compresses the coat and increases heat loss. Shelter and waterproof protection can matter.
Check under the blanket
Sweating, rubs and trapped moisture are signs the setup needs adjustment.
Body condition matters
Thin, senior or ill horses may need a different plan from healthy easy keepers.