Pregnancy Determination in Goats
Pregnancy determination can be performed using real-time ultrasonography and is very accurate with a skilled operator. Transabdominal ultrasound is quick and reliable and can detect pregnancy as early as 25 days, with the fetal heart beat detectable by day 27. Transrectal ultrasound is more difficult and time consuming but can diagnose pregnancy as early as 20 days. The accuracy of transabdominal ultrasound to differentiate the presence of a single fetus from multiples varies from 45%–55% (possibly higher with skilled operators). It is extremely difficult to accurately differentiate between twins, triplets, and quadruplets using ultrasound at any time during gestation. Fetal sexing may be performed by skilled ultrasonographers between days 55 and 70 of gestation and is more accurate in singles versus multiples. Routine radiography can be used to detect pregnancy with 100% accuracy after day 70 and can detect the number of kids after day 75.
Progesterone concentrations can be measured in milk or serum, but samples must be collected precisely one cycle after the doe was bred. Whereas low progesterone levels can confirm a nonpregnant status, high progesterone is not a positive pregnancy test, because it cannot differentiate between midcycle, true pregnancy, or false pregnancy. Plasma progesterone levels in pregnant does have been reported to be higher in triplets versus twins versus single fetuses at 84–21 days before kidding. The estrone sulfate test, performed on plasma, milk, or urine, is another way to determine pregnancy. Between 15 and 20 days after conception, the level of estrone sulfate, a conjugated estrogen produced by the conceptus, increases substantially and stays increased throughout pregnancy. Higher concentrations of estrone sulfate have been reported in does carrying twins or triplets than those bearing a single fetus. Abortion, fetal death, or resorption causes the estrone sulfate level to drop; therefore, the test also is a useful measure of fetal viability. Pregnancy-specific protein B (PSP-B), also known as pregnancy-associated glycoprotein, is produced by the placenta and can be detected in serum or plasma of pregnant does by ELISA at least 30 days after breeding.
Precocious milking is common in heavy-milking strains of goats. It can be seen in a virgin doe or during the first pregnancy. Therefore, udder development is no guarantee of pregnancy.
Hydrometra, or pseudopregnancy, is well documented in goats, although its cause is largely unknown. Aseptic fluid accumulates within the uterus and is accompanied by high peripheral concentrations of progesterone due to a failure of luteolysis. It can be both shorter or longer than a true pregnancy and occurs in 3%–30% of dairy herds. Approximately 50% of pseudopregnancies occur as a result of early embryonic death at ≤40 days of gestation. An additional mechanism involves spontaneous persistence of the corpus luteum, which occurs more commonly in older goats, does bred out of the natural breeding season, or after induced ovulation. In some cases, ovarian cysts may also be present; therefore, it is recommended to always treat for both. Usually, the udder enlarges, but true filling does not occur. The doe may show behavioral signs of impending parturition, possibly even calling or searching for the nonexistent kid. The diagnosis can be made by excluding pregnancy coupled with the presence of clinical signs. This condition can be treated with prostaglandin to lyse the corpus luteum, and does may be able to conceive again if diagnosed and treated early. However, if the condition persists or recurs, the chances of future conception decline. For commercial dairy herds, this can produce moderate to severe economic losses.
Goats tend to have a high incidence of abortion, with chlamydiosis (Chlamydia psittaci) and toxoplasmosis (Toxoplasma gondii) being commonly identified causes in the USA (see Abortion in Goats). In cases of abortion, the fetus and placenta should be submitted to a diagnostic laboratory to exclude infectious causes. Paired serum samples should be obtained from the doe and saved in case serology is indicated. A thorough history, including nutrition and any recent changes in husbandry, should be taken.