Pseudopregnancy in Goats
Pseudopregnancy is one of the major causes of anestrus in dairy goats during the breeding season. Older, parous does are most often affected. It is characterized by the persistence of a corpus luteum in the absence of a (viable) conceptus in the uterus.
Failure of luteal regression, either in nonmated cycling animals or in mated does affected by embryonic or fetal mortality, is the key factor in the pathogenesis of the disorder. Pseudopregnancy can also spontaneously develop in unmated animals, even during the nonbreeding season. Animals experiencing out-of-season breeding are more likely to develop pseudopregnancy. A genetic predisposition has been postulated, but in a study from the UK the incidence of pseudopregnancy in the offspring of affected dams was not significantly different from that in daughters of unaffected does.
Hydrometra (accumulation of fluid in the uterus) is the primary clinical feature of pseudopregnancy. It develops during prolonged and continuous exposure to progesterone from the corpus luteum. When not diagnosed, pseudopregnancy can persist for up to several months, and the amount of fluid can reach a volume of several liters. In such cases, the distended abdomen will give the false impression that the animal is pregnant; this can also be accompanied by udder enlargement.
Low levels of pregnancy-associated glycoprotein will confirm the lack of pregnancy.
Pseudopregnancy can be diagnosed by ultrasonography. The fluid is recognized as anechoic, black spots of variable size, separated by thin, double layers of tissue that represent sections through the apposing walls of the distended, curved uterine horns. When an abundant amount of fluid is present, these tissue layers can be seen undulating when the examiner shakes the abdominal wall of the doe. During an early ultrasonographic pregnancy diagnosis (20–30 days after mating or insemination), it can be difficult to discriminate between a normal pregnancy and a hydrometra because the embryo or placentomes can be difficult to locate at that stage, and excess fluid may be mistaken for allantoic fluid. After day 30 of postmating anestrus, low levels of pregnancy-associated glycoprotein in peripheral blood will confirm the absence of a viable conceptus in goats with or without hydrometra.
Treatment with a luteolytic dose of prostaglandin F2alpha (or one of its synthetic analogues) induces luteal regression and discharge of the uterine fluid within 1–2 days. In some animals a second injection is required to achieve complete discharge of fluid from the uterus. In a recent study from Brazil, uterine fluid was totally drained in 50% (1 dose) and 95% (2 doses) of goats with hydrometra.
If treated during the breeding season, the doe will come into estrus within 2–3 days and can be mated or inseminated again. Sometimes a second injection is necessary to accomplish a complete emptying of the uterus. Pseudopregnancy also may end spontaneously when progesterone production by the (aging) corpus luteum stops. As a result, relaxation of the cervix and stimulation of uterine contractility occur, followed by discharge of the uterine fluid. This latter process has also been described as “cloudburst.” The fertility of does appeared to reach an acceptable rate (up to 55%) after effective treatment with prostaglandins, so culling of affected goats is generally not immediately indicated after diagnosis.