Delivery takes place when the baby releases cortisol, a hormone which signals the mother to begin those activities which result in the expulsion of the fetus. In goats, this takes place on about day 151 of the gestation. The "normal" range is anywhere from 146 to 155 days. If you raise a lot of (full size) goats, you will find that nearly all deliveries take place between 150 and 152 days. The longest gestation that we have experienced is 158 days. Parturition can also be initiated by the death of the fetus, which, although unfortunate, can only be considered a blessing in that it reduces the number of incidences wherein you have to perform this very unpleasant task yourself.
Luckily, a genuine case of prolonged gestation is extremely rare in goats, unlike cattle. It is caused by genetic factors or by maternal consumption of certain plants. A lesion develops in the fetus which prevents the release of costisol.
Obviously, the normal number of days of the gestation period are exceeded. The baby will continue to grow until death takes place, which initiates a half-hearted attempt at labor. There will probably be some udder development with little or no milk production.Treatment and follow up
The first thing to do when you suspect prolonged gestation is to go back to your records and very carefully review your dates. Chances are good that there's an error in your computations. Also, consider a date 21 days later than what you expected on the assumption that she really bred on the next heat cycle.
If you are sure that you do have a case of prolonged gestation you can get an injection from or by your veterinarian to induce parturition or there is a chance that a Caesarian delivery can be performed to save the dam, but there is a good likelihood of a less-than-perfect offspring. The options need to be carefully discussed with your vet.
Since this disorder can be inherited, you may want to cull the doe.