Overview of 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. A genetic predisposition has been postulated, but in a recent 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.
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.
Treatment with a luteolytic dose of prostaglandin F2α (or one of its synthetic analogues) induces luteal regression and discharge of the uterine fluid within 1–2 days. 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 appears to be normal after effective treatment with prostaglandins, so culling of affected goats is generally not indicated.