Pregnancy describes the state of the mare following successful mating to the act of giving birth, called parturition.
How long does pregnancy last?
The average length of pregnancy or gestation length is 340 days. In ponies it is slightly shorter at 333 days. A normal healthy foal may be born anywhere between 325-365 days.
The length of pregnancy can be determined by various factors including nutrition, as well-fed mares will often have shorter pregnancies. Also, the time of year can have a bearing on how long a mare will remain pregnant for. Mares that are carrying foals through the winter months often have longer pregnancy or gestation lengths than those in summer.
How is pregnancy diagnosed?
The traditional method for diagnosis is rectal palpation where a gloved arm is inserted into the mare’s rectum and the foetus or foal felt for manually. Recently, with advances in imaging techniques, ultrasound has become more popular. Ultrasound examination involves insertion of a probe that relays an image back to a screen which can be viewed. The foetus is observed on the screen and this technique often allows earlier confirmation than with manual palpation.
There are two types of blood test which can also be used to diagnose pregnancy. They both look for the presence of a hormone called equine chorionic gonadotrophin or eCG. This hormone is produced by the mare only during pregnancy between days 45 and 100. There is also a urine test available.
Your veterinary surgeon will be able to discuss further the different methods of diagnosis and which one(s) are most appropriate for your mare.