Farmers place a high emphasis on the safety and health of their cows. Just like humans, cows sometimes get sick, and when they do, they may need medications such as antibiotics. Antibiotics are administered only in case of illness to preserve the health and well-being of the animals.
The cow undergoing antibiotic treatment must be clearly identified. The farmer continues to milk her, but her milk must be discarded for a mandatory withdrawal period until her system has cleared the medication. Very strict penalties apply if regulations are not met.
References
Canadian Dairy Information Centre – Agriculture and Agri-Food Canada. National dairy code. 2015.