Okay… so dairy or beef cattle? Cattle come in all kinds of breeds, just like dogs or cats. Some breeds are primarily used for the beef they can produce; some breeds are primarily used for the milk they can produce. Just like certain breeds of dogs are bred for their speed (Greyhounds) or their size (teacup Yorkshire terriers), certain breeds of cows are bred for their ability to make milk (Holsteins or Jerseys) or to grow muscle (Angus or Hereford).
Dairy breeds of cows are capable of making much more milk than one calf would need. Some dairy cows can produce up to eight gallons of milk a day. Most beef cows just produce enough milk to keep one (and sometimes two) calves fed and happy, but not much extra. This is usually 1-2 gallons a day.
These photos are all of dairy cows (all girls). The first four cows are Holstein cows.
This cow is not lactating right now. She is pregnant, and is getting ready to calve (have a baby) in about two weeks. As a pregnant dairy cow who is not lactating, she weighs a little more than cows who are lactating.
This Holstein cow calved about two months ago and is lactating (milking) now. She is in the breeding pen at her farm, so hopefully she will be pregnant again soon. You can see that this cow is skinnier than the cow in the photo above. That is normal in dairy cattle. They make a lot of milk, so even with appropriate nutrition they tend to get skinnier while they are lactating.
This Holstein cow is in the same pen as the one above. She calved about two months ago and is milking now. She is also in the breeding pen, so hopefully she will also be getting pregnant soon. Just like people, cows need to have a baby before they can make milk. The cows get a break from milking when they are getting close to calving – that way most of their nutrition can go into growing the baby instead of making milk.
This is a Brown Swiss cow. A Brown Swiss is just a different breed of cow (like Labrador retrievers are a different breed of dog from Golden retrievers), but they are still very good at making milk. She is about half-way through her lactation. Brown Swiss have a different body type than Holsteins, and don’t tend to get quite as skinny, but you can see this cows’ ribs a little bit, and her hip bones are sticking out just a little. Again, this is normal in dairy cattle. They are built differently than beef cattle, so they should look different.