I do not feel uncomfortable with Canadian Manufactured Drugs.
Durvet is made about 20 miles from my house.
DURVET, INC. ANIMAL HEALTH PRODUCTS P.O. Box 279 · Blue Springs, Missouri 64014
According to the Tractor Supply site, and my own in hand inspection, the Durvet ivermectin paste for oral use is ‘imported’. Per the Tractor Supply site the ivermectin for injection is made in USA.
I see no Jeffers horse products, but cat/dog products appear to be made in the USA.
Drug houses may outsource production for their brands.