Why?
It takes a lot to prepare cows to not be milked. They're not going to be milked from now until they have a calf. This way, their bodies can concentrate all their resources on getting ready to have a calf. Then, after they have calves, they'll be ready to produce milk again.
So, you may wonder, if our cows are dried up, how are we making any money? We aren't! We accept both cash and personal checks.
No, really, we use bulls, and all the cows don't get pregnant the same month. Some of them get pregnant later, so we don't dry all of them up at the same time. (Just most.) So the ones that aren't as far along we still milk until it's their time to get dried up. By that time, cows will have calved and we'll still have milk in the pipeline.
My sister has again been using my blog as a way to inspire journal writing in her middle school classroom, so for them, I'll walk you through the steps of drying up ... (see what they ask about this!)
1- The guys push on the right side of the cow's stomach to see if they can feel a calf. This is called 'bumping'. Most of them are about seven months along, and their gestation period is nine months, so you can usually tell. (I think they look pregnant just by eyeing them, but I know it's not polite to ask.)
2 - If she's pregnant, they give her an antibiotic squirt in each teat of her udder to prevent infection. She won't be milked again for at least a month, so the antibiotic will be out of her system long before she is milked again. (There are no antibiotics in milk that goes to the store, ever. If a cow is ever given medicine, she is not milked into the bulk tank until it's out of her system. Every milk load on every farm is tested every day, multiple times. For more about how antibiotics are not in your milk at all, ever, read here.)
3 - They finish by putting a sealant called T-HEXX on her teats, which prevents bacteria from entering them.
4- They mark them with a cow marker on their hind quarter to separate the dry cows from the cows that are still being milked.
5 - The vet checks the remaining ones manually (by which I mean she gives them a pelvic exam) to see if she can feel a calf. Either the cows aren't as far along in their pregnancies, or there are always some that didn't get pregnant at all.
Then, we stop milking the really pregnant cows. They were mooing at us last night, wondering why we weren't milking them like we have twice a day for a YEAR. I tried to explain it to them in a soothing manner, but they mooed right over me. It's so hard reasoning with pregnant ... anythings.