Managing the broodmare for maximum reproductive efficiency is an integral part of a successful equine breeding program. Mares have the lowest reproductive efficiency of all domestic farm animals, with only 60-65% of those bred annually in the United States producing live foals. Although there are many reasons for this inferior reproductive performance, endometritis and irregularities of the estrous cycle represent two major contributing factors.
Endometritis is defined as inflammation of the endometrium or internal lining of the uterus. It has been shown that up to 40% of the mare population may have some degree of endometritis. This inflammation is usually caused by a bacterial infection, but other irritants such as urine or air aspirated into the uterus are important additional causes.
It is critical that a reproductive examination of the mare is performed prior to exposure to the stallion. In some cases of endometritis it can lead to venereal infections which may permanently infect the stallion. A reproductive examination includes an external evaluation of the genital tract giving special attention to the conformation of the vulva. Faulty conformation predisposes mares to endometritis. An internal rectal examination will allow the veterinarian to palpate ovaries, cervix, and uterus. Past history of the mare and findings of the internal examination may indicate the need for further tests. Samples of the uterus may be needed for bacterial culture and cytology to assess the presence of harmful cells. A biopsy may be needed to find harmful cell types which reside below the surface.
Irregularities of the mare’s estrous cycle can lead to subnormal fertility. The average, normal mare should ovulate preceding ovulation and the remaining 16 days of the cycle be non-receptive to the stallion. Proper teasing and record keeping is critical to identification of these abnormal mares.
Mares that exhibit irregular cycles should be examined so that proper treatment or hormonal therapy can be instituted. The use of ultrasound examinations has been of tremendous benefit in the diagnosis of reproductive problems as well as early pregnancy diagnosis.
Preventative measures including reproductive examinations prior to breeding, reduced contamination at breeding, and early pregnancy diagnosis using ultrasound as early as 12 days following breeding have become essential elements in broodmare management.
– Dr Mitch Hutchinson, D.V.M.