This is Penny. Penny is a lactating cow at a local dairy. She produces about 120 pounds of milk per day- she’s a very high producing cow and the dairy owner is very happy to have her in the herd.
One day, Penny comes down with mastitis, which is an infection of her mammary gland. The farmer is very upset to see that she has the infection, because this means that she has to be removed from the milking herd until it clears up. The farmer calls out the veterinarian that tends to the herd. The veterinarian confirms the diagnosis of mastitis and determines that it is in Penny’s best interest to prescribe her a round of antibiotics.
ANTIBIOTICS?!?! Yes, sometimes dairy cows get antibiotics. Think about what happens if your child gets sick. You will probably take him or her to the doctor, and depending on the sickness, he or she will get antibiotics. You don’t want your child to suffer from a treatable illness, and the same goes for farmers and their cows! Some illnesses can be treated with antibiotics, but there are precautionary steps in place to make sure that this doesn’t affect the milk supply.
First of all, Penny will get a red band around each of her hind ankles. This signifies that she is being treated with antibiotics and thus must not be milked with the rest of the herd. Just because she has mastitis, though, does not mean she stops producing milk, so she still must be milked to prevent other problems from happening. She will be milked after the rest of the herd, into a bucket which will then be discarded. Her milk never reaches the bulk tank- therefore, antibiotic residues never reach the tanker truck, processing plant, grocery store, or your house.
But farmers could just ignore those steps and still milk them into the bulk tank, right? Well, they could, but the industry makes it so they really, really don’t want to. How so? When the tanker truck comes to the dairy to pick up the milk from the bulk tank, a sample is taken from the farm. The tanker truck is probably going to multiple dairies at a time, so they will take a sample from each farm’s bulk tank before loading the milk on to the truck. Those samples will be tested for antibiotic residues before the milk is offloaded at the processing plant. If any sample comes back positive for antibiotic residues, the farmer whose sample it was has to buy the whole tanker truck of milk from the processing plant, because the whole truck is contaminated due to the mixing of all the farm’s milk together. The milk will be discarded from the tanker truck, which is then cleaned and sanitized as it is after every trip. That provides a pretty good incentive for farmers to not milk treated cows into the bulk tank, right?
Meanwhile, Penny is finished with her round of antibiotics. The farmer pays attention to the withdrawal time of the medication to know when she can be milked with the rest of the herd. Suppose the medication that Penny is on has a withdrawal time of 60 hours. If she receives her last dose of medication on a Monday at 6:00 am, her milk has to continue to be discarded until Wednesday at 6:00 pm. After that time, she can rejoin the milking herd and continue to produce healthy, nutritious milk!