What are the signs of pregnancy in a jersey cow?

Until her udder and vulva start to swell late in her third trimester, the only way to tell a cow is pregnant by looking at her is that she's getting pretty round in the sides. You can also bump her side gentely with your fist and feel the calf inside her. The best way to find out is to have your vet do a pregnancy check on her.

To determine if a dairy cow is pregnant, feel the area immediately to the SIDE (left or right) of the base of the tail. If it is hard, the heifer or cow is not pregnant, if it is soft, she is pregnant. I recall this from many many years ago when I was a teenager working on my uncle's dairy farm.

Another way is to see if the cow comes in to heat again (21 day cycles). This is demonstrated by bulling behavior. A cow in heat will stand and allow another cow to mount her or attempt to mount another cow. If the cow being mounted walks away from the attempt, then in all probability the cow that was on top is in estrus.

See the related question below for more info.