Ultrasonic echography in the mare.

Ultrasonic echography in the mare allows pregnancy diagnosis as early as Day 14 after ovulation. In the 1980 and 1981 breeding seasons, a total of 7438 examinations of 4688 mares were performed on several farms with the same apparatus. The accuracy of positive pregnancy diagnosis was estimated to be greater than 95% and of non-pregnancy diagnosis greater than 84%. When abnormal pictures of vesicles are found, it has to be decided whether it is a conceptus or a cystic structure. Most small vesicles do not develop, whereas large ones, deformed shapes, presence of some echoes, or a division inside the vesicle most often represent a growing conceptus or sometimes twins. Twinning rate in early pregnancy (before Day 30) lies between 2.6 and 2.8%. Twins are suspected when there are 2 vesicles of equal size (observed successively rather than simultaneously) (50-60% are confirmed), unequal size (less than 9%) or one oversized vesicle (23%), one of an irregular shape (5%) or a divided vesicle (33%). No effect of the month of mating on the rate of twin conceptions was found. Early pregnancy loss (between mean Days 23 and 43) was estimated at 5.3% and total embryonic loss (early and late) at 9%. Rate of embryonic death increased in proportion to the interval between the two successive diagnoses. No critical period of early mortality or effect of the reproductive status on embryonic or fetal mortality was found.