Shedding ?

Has anyone encountered heritage breeds shedding? I have a one year old pregnant Hereford gilt that started loosing her hair about a month ago. I wormed her with ivermectin in Feb. First dose of litterguard a week ago. Eats, drinks, acts fine. No fever. No sign of mites or mange anywhere. She is group housed with three other hogs (1 Hereford and 2 blue-butts)they are all fine. It was a bitterly cold winter this year, many days below 0. Her coat was very dense up till she started loosing it.