My first year with pigs, the earliest butcher date available, booked the day the piglets were born, was mid December. (I should make a
thread to rant about the fucked up government-enforced monopoly slaughterhouse regulations in BC... another day..)
I built a three sided shelter, dirt-floored shelter for the hot months, boarded up the open(long) side when it got cold, and put down a bunch of straw. The reading I had done agreed that this was OK...
It was not OK here, they got pneumonia, too close to butcher date for drugs. I was fortunate that I was spending
enough time observing them to catch it early, and that a more experienced friend could promptly diagnose the symptoms.
I moved them into a cement floored barn, with a nest area floored with
pallets and provided with additional draft-blocking plywood. That plus garlic, sage, and electrolytes let them recover PDQ without any drugs to screw up my meat.. but it was definitely not a fun
experience!
The issue seems to be that it is cold but also damned wet here, and I needed to have them off the ground, not just well bedded with straw...
I now put down a floor in their shelter in October, to be safe. I butchered a couple weeks ago this time, so can't say whether that would have gotten me all the way through...
So, does your shelter have a floor?
I would imagine things are less soggy and more cold there, so maybe easier on the animals?