Induced Abortion or Parturition

Induction of abortion or parturition is easily accomplished in the doe.

Indications

Management errors and eager bucks often result in the natural breeding of goats that the owner did not wish to become pregnant.

Owners or veterinarians may desire to induce parturition in goats for a variety of reasons. Disease or injury to the doe may make survival to term and completion of normal parturition unlikely. Pregnancy toxemia appears to fit in this category, but cases must be evaluated carefully. As dis­cussed later, early-pregnancy toxemia responds to medical treatment, assuming underlying causes of anorexia can be resolved. Goats with advanced-pregnancy toxemia com­monly die before the hormonal sequence of events culmi­nating in induced parturition can be completed (often 36-48 hours in a sick doe). These animals require surgical intervention.

Fractures, arthritis, and laminitis may be easier to man­age if the goat can be relieved of the weight of fetus, pla­centa, and associated fluids. If a disease or injury in the late-pregnant doe is expected to interfere with feed con­sumption for several days, (induced) parturition may pre­vent the otherwise inevitable development of pregnancy toxemia.

Another very important indication is the convenience of predicting the time of parturition. Owners may wish to be present to offer assistance to a primiparous or aged doe.

Drugs Used

The normal sequence of hormonal events in the initiation of parturition has been described as beginning with an increase in fetal cortisol, which increases placental secre­tion of estrogen. As maternal estrogen concentrations rise, the uterus produces prostaglandin F2 alpha, which causes luteolysis and a drop in progesterone. High estrogen and low progesterone levels together permit uterine contrac­tions to occur and labor begins (Flint et al. 1978). There is a final surge of prostaglandin in the last few hours before delivery (Umo et al. 1976).

Historically, three classes of drugs have been used to induce parturition.

Corticosteroids

Corticosteroids (e.g., dexamethasone, 20-25 mg) act by increasing placental estrogen synthesis. Generally, the fetus and placenta need to have reached a stage of maturity where placental C21-steroid 17alpha-hydroxylase activity can be induced (Flint et al. 1978). This is approximately the same stage of maturity required for survival of the fetus, or roughly 141 days. Younger fetuses may fail to respond, which may be desirable if fetal survival is important, or undesirable if rapid termination of pregnancy is impera­tive. The average time to parturition in goats receiving cor­ticosteroids has not been well characterized, but is approximately 44-48 hours in animals close to term. In one study in which four does received 20 mg dexamethasone 10 days before their due date, the average time to delivery was 55 hours (Jain and Madan 1982, 1989).

Estrogen

The second group of hormones to be used is estrogens (e.g., estradiol 17-beta, 16 mg). The time to parturition is similar to that for corticosteroids, but abortion of non-viable kids can be expected if treatment is attempted too early in gestation. In a study of 36 goats each given two doses of estradiol benzoate (15 or 25 mg on days 147 and 148), most of the does kidded on day 149, but five of the does receiving the higher dose did not conceive in the next season (Bosc et al. 1977).

Prostaglandin

Currently, the most popular means of ending pregnancy is prostaglandin. Because the goat depends on progesterone from corpora lutea to maintain pregnancy (the placenta does not produce progesterone), prostaglandins are theo­retically effective at all stages of gestation past day five. Thus, if a “buck escape” occurs, all does for which breed­ing was not desired can be treated with 5 mg prostaglandin F2 alpha 7-10 days later. Attention must be given to ade­quate buck restraint when many does return to estrus simultaneously two days after prostaglandin treatment. Because the occasional doe is not aborted by this treat­ment, a second dose of 5-10 mg might be given to animals not seen to return to estrus. In a study involving does that were approximately three months pregnant, two doses of 5 mg of prostaglandin F2 alpha 24 hours apart resulted in abortion between 34 and 81 hours after the first injection. Retained placenta occurred in 31 of 41 does thus aborted (Memon et al. 1986a). Thus, abortion in mid-gestation using prostaglandin appears to take longer than induction of parturition at term. In addition to the increased risk of retained placenta, there are anecdotal reports of difficulties rebreeding does thus aborted in the same breeding season.

The owner who plans to induce parturition (as for CAE control) must faithfully record all breeding dates and pre­vent later reexposure to a buck. Alternatively, biparietal diameter of the fetuses can be determined by real-time ultrasound, as described above, to date the pregnancy. Injection should not be performed until day 144 of gestation or later, because triplets or quadruplets may be so small as to have reduced viability (Williams 1986b). Corticosteroid pretreatment 12-24 hours in advance may hasten lung mat­uration and improve viability if early induction is necessary.

There is some question as to the dose of prostaglandin required. Doses of prostaglandin F2 alpha (Lutalyse®, Zoetis) as small as 2.5 mg might be expected to work, but several authors have suggested that higher doses (up to 20 mg) nar­row the time period when parturition is expected to occur (Bretzlaff and Ott 1983). Reported studies have involved too few goats to justify this conclusion. Many producers use 7.5-10 mg, given intramuscularly in the morning, with most parturitions expected the next day, 29-36hours later. If the prostaglandin is given in the evening, a similar interval to parturition results, such that the kids are delivered during the night (Romano et al. 2001). An appropriate dose of the synthetic prostaglandin cloprostenol (Estrumate®, Merck Animal Health) is 62.5-125 μg (Williams 1986b) or 150 μg (Maule Walker 1983). A Brazilian study documented that 75 μg was an adequate dose, as 100 μg did not improve the response (Santos et al. 1992). Another synthetic prostaglan­din, luprostiol, has been used in Europe. When given intra­muscularly on day 145 at a dose of 3.75 or 7.5mg, parturition usually occurs in 30-40 hours (Batista et al. 2009). Fenpros- talene has been used successfully at 0.5mg subcutaneously, with a mean interval to kidding in 11 does of 32hours (Haibel and Hull 1988). Pollock et al. (2021) administered 10 mg of prostaglandin F2 alpha and 10mg of dexametha­sone at 4 p.m.

Retained placenta and sometimes metritis have been reported after prostaglandin-induced parturition (Bosu et al. 1979; Maule Walker 1983), but are not common in the experience of other researchers (McDougall 1990; Romano et al. 2001; Pollock et al. 2021) or owners who routinely induce parturition in their does. In one report from New Zealand, cloprostenol was administered to 360 pregnant goats, 14 of whom died with Clostridium chauvoei infection and toxemia, though they did not have retained placenta. The authors recommended that clostridial vaccination be given before abortion is induced (Day and Southwell 1979).

Experimental Techniques

In herds in which exact breeding dates are not known, it may still be desirable to have parturitions occur during the day. Observation, assistance in case of dystocia and proper identification or early removal of kids are all simplified. Other approaches might be applicable when prostaglandin cannot be used to safely modify the time of parturition. Two techniques that have been tried on sheep are control­ling the time of feeding and administering a tocolytic drug to delay parturition. Thus, sheep fed once a day tend to lamb during the period from four hours before to eight hours after feeding (Gonyou and Cobb 1986). Clenbuterol (0.2 mg per ewe) delayed parturition for 10 hours or more in most ewes judged to be very near to lambing (Plant and Bowler 1988), but use of this drug is forbidden in the United States. Because kidding occurs naturally during the day (Bosc et al. 1988), these techniques have received little attention in goats.