First of all, I don't know any dairy farm that has enough milking machine units to keep each cow hooked up all day every day. That isn't practical and the logistics don't work, for starters. Each dairy is different and has different routines, procedures, milking times and facilities. So while one dairy may be able to milk 10 cows at a time with 5 cows on each side, another with more cows may be able to milk 40 with 20 on each side. There are larger parlors and smaller parlors too.
Most dairies milk their cows 2 or 3 times every day. There are some that will milk the fresh cows that have recently had a baby in the last few weeks 4 times a day. This is only for a few weeks and can help the cows. In my experience with this, these few cows were milked at the beginning and end of each milking.
This is a milking machine that's not in use at the time. The four "arms" are rubber inflations covered by a stainless steel shell. Inflations are changed every so many milkings to make sure the rubber is in good condition. The pulsators attached to the milking machines create an alternating motion that simulates hand milking but is much quicker than milking cows by hand. It's much easier to show people this than try to explain it. It feels like a massage and is not rough for the cows.
Okay, okay, so we know that every farm is set up differently, not every dairy farmer starts milking at 4 a.m. and that the routine may change throughout the cow's lactation, but how long are they hooked up to the milking machines each time?
The answer may surprise you. It's less than ten minutes each time. This will vary depending on many factors including how much milk she's giving, how fast she lets down her milk, what breed of dairy cow she is, etc. Cows that give more milk are usually in the first 6-8 weeks of their lactation (length of time after having their baby and starting their lactation) and since they are giving more milk, it takes longer to milk them out. Some cows just are slow milkers, though. Usually, we can figure out who these ladies are and hook them up first so they don't hold up the whole group. Usually, all the cows on a side of the parlor have to be done and their teats dipped with an iodine solution to protect their udder from any bacteria it may encounter while the cow is laying down in the barn. Different breeds of dairy cattle produce different amounts of milk. Holsteins (the black and white ones) produce the most by volume, while Jerseys (the little brown cows) produce less milk but the milk has higher components (fat and protein, which is important when making products like cheese). To learn more about each of the six major breeds of dairy cows, click here.
For more about how dairy farmers make sure the milk supply stays safe and free from antibiotic residue, click here.
Other questions related to milking cows? Leave it in the comments! I may cover it in a future Dairy FAQ post!