Late Abortion: Non-infectious Causes
Although multiple late abortions suggest the presence of one or more infectious agents in the herd, nutritional, hereditary, and toxic etiologies should not be overlooked.
In addition, inadequate nutrition increases the prevalence of abortion caused by infectious agents such as Q fever and others that compromise placental function.
Malnutrition, Stress, and Other Environmental Factors
Stress abortions are common in undernourished Angoras on range and are occasionally seen in other breeds in the United States. When inadequate energy or protein is fed in late gestation, kids may be aborted or stillborn, or born alive but small or weak. Colostrum and milk production may be inadequate for survival of the live-born kids. If the major deficiency is one of energy, pregnancy toxemia is likely to occur in does carrying multiple fetuses. If just protein is lacking, the does may not be thin or ketotic. Reduction in the size of the fetal thymus has been proposed to be an indication of a stress abortion. In Mexico, producers associate cold and rainy weather with abortion in dairy goats, often primiparous animals. A greatly increased maternal cortisol level has been documented to precede some of these abortions (Romero-R et al. 1998).
The underlying cause in a nutritional abortion outbreak may be poor-quality (grass) roughage, inadequate feeder space, or very cold weather. Young, undeveloped females should not be bred if feed conditions are unlikely to permit them to complete gestation successfully.
An epidemiologic study of 22 dairy goat herds in Norway revealed fetal loss in 11% of the 1439 goats, with losses in individual herds varying from 3 to 38%. In almost all herds there was no evidence of infectious disease. Decomposed fetuses were typically expelled during the last two months of pregnancy, and mature does (at least 3 years old) were at greatest risk.
Inadequate natural lighting in the barn, more goats per pen, and less floor space per goat were identified as possible risk factors. Progesterone and cortisol were normal before abortion, but estrone sulfate was reduced, suggesting placental malfunction (Engeland et al. 1998b, 1999).Inherited Abortion of Angoras
In South Africa, where selection for fine-quality mohair has been intense, a genetic habitual abortion problem has been identified in older does (Van Rensburg 1971b; Van Tonder 1975). Appropriate culling has reduced this problem in the breed.
Pathogenesis and Clinical Signs
The newborn doe kids destined to become habitual abort- ers (and the buckling that carries the trait) are above average in weight and have a very fine haircoat. As the animals mature, they produce higher than average mohair yields because of decreased adrenal function. The doelings show heat and conceive better in the first breeding season. The apparently desirable offspring of the first few pregnancies are kept for breeding, thus perpetuating the trait in the herd.
Habitual abortion usually does not appear until does reach 4 or 5 years of age. Animals with the greatest mohair production relative to body size tend to abort at approximately 100 days' gestation, a time when fetal growth rate increases but placental growth ceases. Adrenal malfunction is involved. Death of the fetus apparently occurs because of placental insufficiency (Van Rensburg 1971a). Luteal function is not impaired, and dead edematous fetuses may be retained for days or weeks. Stresses such as inclement weather, shearing, and dipping promote the expulsion of dead fetuses, causing an apparent abortion storm in the herd.
The older aborter develops both pituitary and adrenal hypertrophy, which are believed to be compensatory for previous adrenal insufficiency. These does have short estrous cycles and a lowered conception rate. A decreased amount of finer mohair is produced. Some of these does show other external evidence of hyperadrenalcorticism, such as muscle wasting and abdominal distension.
Prevention of Habitual Abortion
Mature does that abort or fail to conceive should be removed from the breeding flock. This policy has been shown to decrease the frequency of abortion in Angora herds (Van Heerden 1964). However, under certain nutritional and environmental conditions, progress in decreasing the flock abortion rate is minimal (Van der Westhuysen and Wentzel 1971). The previous offspring of aborters should also be culled. Breeding males in particular should be selected from older does with no history of abortion.
In addition, adequate dietary energy should be supplied for pregnancy maintenance, because both the habitual aborters and “normal” Angoras are more apt to abort if underfed. If a correct diet cannot be supplied, provision of shelter reduces the abortion rate in times of cold weather (Van der Westhuysen and Roelofse 1971).
Caruncular Amyloidosis
Beginning in 2012, a syndrome of last-trimester abortion, stillbirth, or mummification was observed in at least four dairy goat herds in California (Rowe and Woods 2016). The does were of Toggenburg, Saanen, and LaMancha breeds and they showed no signs of illness when aborting, although placentas were usually retained. Extensive laboratory testing revealed no infectious agents, although some fetuses exhibited leukoencephalomalacia and mineralization of the brain or myocardial necrosis. Caruncular amyloidosis was initially discovered when aborting does were sacrificed, but later cases were diagnosed from caruncular biopsy taken at the time of abortion. The amyloid present in the caruncles was identified as serum amyloid A3 and had not been previously associated with fetal death (Gaffney et al. 2015). The occurrence of the disease in multiple breeds does not support a hereditary cause, but an infectious agent has not yet been identified. Presumably the amyloid interferes with transfer of oxygen and nutrients to the fetuses.
Vitamins and Minerals
A severe vitamin A deficiency (caused by six months on dry pasture without green grass) was implicated as the cause of 32 abortions in a goat herd in Brazil (Caldas 1961).
Vitamin A concentrations were undetectable in aborting does.Selenium deficiency can be a cause of abortions and stillbirths in localities where feedstuffs are low in this mineral. Manganese, iodine, and copper deficiencies have also been shown to cause abortions and weak kids (Anke et al. 1972, 1977; Hennig et al. 1972; Singh et al. 2003). Some aborted fetuses are mummified when does are fed copper-deficient rations. If copper deficiency (or molybdenum or sulfur excess; see Chapter 19) is the cause of abortion or stillbirth in the second to fifth months of pregnancy, some kids in the flock might be expected to be born with weakness or swayback, as described in Chapter 5. Demyelination of white matter in spinal cord and brain has been observed in fetuses aborted due to copper deficiency (Moeller 2001). Liver copper concentrations should be determined to verify the diagnosis. One herd of African dwarf goats experienced 54% loss by 2 weeks of age until pregnant does were supplemented several times with 10 mL of a 2% solution of copper sulfate (Senf 1974). If iodine deficiency has caused stillbirths, affected kids usually have goiters. Conversely, however, goitrous kids in endemic iodine-deficient areas might be aborted in response to an additional etiologic agent (Wilson 1975). Thus when trace mineral deficiencies are detected in aborted fetuses, the maternal diet should be corrected, but further investigation for infectious causes is still imperative.
When goats are kept for several generations under conditions of a trace element deficiency, such as manganese, there is selection for animals that are less susceptible to the deficiency (Hennig et al. 1972). This means that imported goats may show abortions and stillbirths under conditions that permit native goats to reproduce successfully.
Toxic Plants
Several toxic plants have been associated with abortion or birth defects in goats, including Gutierrezia spp. (broomweed) (Dollahite and Allen 1959; Dollahite et al.
1962; Gardner et al. 1999), Astragalus Ientiginosus (Furlan et al. 2007), Lupinus formosus (Panter et al. 1992), Conium maculatum (Panter et al. 1990), Nicotiana tabacum (Panter et al. 1990), and Veratrum californicum (Binns et al. 1972) in the United States. Ponderosa pine (Pinus ponderosa) does not cause abortion when fed experimentally to goats (Short et al. 1992). The normally nutritious pods of the Acacia nilotica tree in South Africa cause abortion and methemoglobinemia when large amounts are consumed (Terblanche et al. 1967; Kellerman et al. 2005). Mimosa tenuiflora has caused extensive birth defects of the limbs, spine, head, eyes, and brain in goats and other livestock in Brazil (Pimentel et al. 2007; Dantas et al. 2010) and experimentally Ipomoea carnea has caused abortions and birth defects in goats in Brazil (Gotardo et al. 2012). Other plants causing reproductive failure and malformations in goats in Brazil have been reviewed by Riet-Correa et al. (2012). Experimental oral administration of Claviceps purpurea sclerotia (ergot) has caused abortion and fetal mummification (Engeland et al. 1998a). Likewise, aflatoxin in contaminated feed ingredients has caused abortion in goats in India (Maryamma et al. 1990). Additional plants are documented to cause congenital defects in sheep: Astragalus (abortions and limb defects), Lathyrus, and Sophora (limb defects) (Szabo 1989). Akabane, Schmallenberg, and Cache Valley viruses produce similar malformations.Drugs
The pharmacokinetics of a few drugs have been studied in pregnant goats (Davis and Koritz 1983). In does pregnant 110-115 days, three fetuses were aborted from seven does given 4.4 mg/kg chlorpromazine intravenously. These fetuses showed histologic evidence of major liver damage. Bromocriptine at a dose of 2.5 mg/kg intramuscularly also induced abortion in goats in the last trimester (Al-Hamedawi et al. 2009). When phenylbutazone was given intravenously to six does at 33 mg/kg at the same stage of gestation, two kids had renal insufficiency and histologic kidney lesions after birth.
Anthelmintics, because of their frequent use during pregnancy, and corticosteroids have been implicated as causes of abortion.
Phenothiazine
Abortions have been observed in sheep and goats given phenothiazine as an anthelmintic in the last month of pregnancy (Osweiler et al. 1985). Photosensitization and associated bilateral keratitis may also occur and are well documented to be caused by phenothiazine.
Levamisole
Levamisole (the levo-isomer of tetramisole) is an anthelmintic that has been used extensively in goats, although it is not approved for this purpose in the United States. Word- of-mouth reports of abortions in goats have led to a general, conservative recommendation that the drug not be used in late pregnancy (Guss 1977); oral use is considered to be safer than systemic administration. These abortions have not been reproduced experimentally. Likewise, tetramisole did not cause abortion in Angora goats (Philip and Shone 1967). More recently, a possibly genetic polymorphism in the metabolism of levamisole (mediated by hepatic P450 isozymes) has been identified (Babish et al. 1990). The greatly prolonged half-life of levamisole in some goats might contribute to occasional toxicity, or the temporal association of abortion after levamisole administration might be caused by chance alone.
Corticosteroids
Corticosteroids are sometimes administered for an antiinflammatory effect to goats with infectious disease or with injuries. This should be avoided during the last month of pregnancy. The intentional use of drugs to induce parturition is discussed below.