It is important to know when a cow will calf, so that you can be there to assist during the birthing process, if she requires it. There are several ways to predict when a calf will be born. It is always best to leave a cow alone when she has her calf, but being nearby will allow you to call a vet, if necessary. It also increases the chance of a calf surviving those critical first 24 hours.
If the cow was artificially inseminated or you have records of the actual mating, calculate the expected birth date using a gestation calendar. Pregnancy is about 283 days, but can span 10 days either way. Monitor the cow from 15 days before the expected due date.
Inspect the cow's udders. In most cases, these will fill with milk about 3-7 days before calving. This method can only be used as a rough guide, because a cow's udders can fill with milk as early as six weeks prior to calving, or in the final 24 hours.
Look at the cow from behind and see if her vulva looks swollen. This is called springing. It is a sign that she is approaching her calving date. This can happen several weeks before calving, but if it is accompanied by a mucus discharge, it is a sign of impending labour.
Check the back of the cow for the area between the tail head and pin bone (point of the buttock). See if it appears sunken. This indicates that the pelvic ligaments have relaxed. Labor will begin about 12 hours after this happens. If your cow is used to being touched, feel this area to determine if the ligament is loose.
Monitor the cow for behavioural changes. If the cow is in a herd situation, she will try to separate from the other animals. This usually happens in the final 24 hours before the birth. She may not come for her regular feeding.
Watch for the cow repeatedly lying down then standing again, swishing her tail and being generally restless. That indicates she may be in the first stage of labour. Observe whether she holds her tail out and appears to be straining. Watch for the water to break. The calf's legs should appear a short time later.
When the cow isolates herself from the herd, monitor her from a distance using binoculars. She wishes to be alone and will try and get farther away if approached. If there is a storm coming, cows often will calf early, so be aware of this.
Call a vet if a cow is in labour longer than 4 hours. If two legs appear and the bottom of the feet are pointing to the sky and not the ground, it means the calf is in the wrong position. Immediately call a vet, or get a person experienced in birthing calves to turn it.