I'm a cow, I let Joy shiver as she has weight to lose. The only time I rug her is if she is being tied up for prolonged periods so she can't move about to keep warm. Littles never shivers, even when tied up, as he has a thick coat you can lose your arm in.
I'm seriously going to have to revisit the muzzle with her. She's at her best weight every summer because I restrict her grazing so much and run a track system. Its when the wet comes I have a problem as we are on clay so they have to have access to as big an area as needed to protect the ground. She always gains weight over winter despite being out 24/7/365, with no hay, rugless and with a neck and belly clip!
The reason I think the little man with need a rug is that he didn't gain last winter. I may well need to add more to his feed too if needed. We'll see.