Producers will no longer be allowed to continuously feed animals low-level doses as a way to promote growth.
Dr. Trisha Dowling, a pharmacologist with the Western College of Veterinary Medicine, says penicillin and tetracycline have long been fed to livestock in order to reduce the workload of animals' immune systems, thereby causing them to grow faster using less feed.
She says in many cases, products specifically marketed as growth-promotants are older drugs that have fallen out of use in humans as bacteria have developed resistance.
The rules do still allow in-feed antibiotics as a preventative measure against disease.
Dowling says that in many cases, the exception means business-as-usual for producers.
She says this was especially true in the poultry industry, where improved growth is essentially a side benefit for producers using the drugs to prevent infections that can wipe out whole barns if they get a foothold.
"If you don't put (antibiotics) in the feed, and you wait until you get an outbreak of necrotic enteritis, you've got a lot of dead birds and you've lost a lot of money," she said.
On the cattle side, Saskatchewan Cattlemen's Association CEO Craig Douglas said most producers don't feed antibiotics.
"Without singling out any other industry -- it's other sectors where that's been more of a standard procedure," he said.
Douglas said most ranchers only reach for the antibiotics when an animal is clearly unwell.
"They're not medicating their animals unless their sick," he said, adding that costs as high as $500 per animal tends to keep the use of injected antibiotics in check.