Venereal Diseases and Pregnancy Loss
Venereal Diseases are diseases which are transmitted sexually. These diseases can be transmitted during natural breeding or may be transmitted via the semen. These diseases can be "clinical" (readily apparent) or "subclinical" but able to be passed on to other horses from a "carrier" horse. Some infections can cause endometritis in the mare, early embryonic death, abortion, the birth of a sick foal or systemic disease in the stallion or mare.
Although fertilization rates approach 90% of mares for all mares bred, pregnancy rates on the the farm is only 80% for reproductively healthy mares and 55% per estrus for all mares. Early loss (day 14-60) accounts for 10-12% decrease in pregnancy rate. Factors leading to early pregnancy loss can be extrinsic (factors outside the mare) or intrinsic (factors related to the mare). Later abortions can be divided into infectious and non-infectious caused losses.
Abortion is the termination of a pregnancy before the fetus is capable of extra-uterine life (<300 days). The term abortion is usually used for a pregnancy loss after day 60 in the mare. It is observed that 5-15% of pregnancies end in abortion. Most abortions are secondary to placental dysfunction although some abortions are caused by fetal death. If the pregnancy is lost before 4 months, no fetal or placental membranes are observed (may be absorbed in utero). Losses after 6 months are usually observed and can be used to diagnose the cause of the abortion.
