Infectious, nutritional, toxic, environmental, genetic… there are many potential causes of fetal loss in livestock species. This article will focus on the most common causes of miscarriages in sheep and goats.
Excellent records will facilitate recognition and diagnosis of abortions. Losses of 1 to 5% annually can be normal in a given herd; careful record keeping and analysis will indicate a problem is at hand while there still may be time to intervene. Genetic defects, stress, weather flukes and nutritional mishaps will always conspire to make a few animals miscarry, but several management and infectious causes can result in huge abortion wrecks.
Early Embryonic Death vs. Abortion vs. Stillbirth
Abortions early in gestation are termed “early embryonic death” (EED) and manifest themselves as irregular or repeated heat cycles; no conceptus or discharge is usually noted from the dam, who resorbs the embryo and fluids. If the fetus dies in mid or late gestation, sometimes the fluids are resporbed and a mummy results. The dead mummy can be “born” along with live siblings at the normal labor time or it can be retained as a singleton in the uterus indefinitely as long as no infection ensues; such an animal will appear to be in a non-advancing pregnancy and will not come into heat again unless treated to expel the mummy. Most mid- and late-term fetal deaths partially decompose and are expelled from the dam before the date of fetal viability; the placenta is often retained in these cases, which can lead to uterine infections. Stillbirths are deliveries of dead fetuses that are old enough to have survived had something untoward not happened to prevent them from taking their first breath. Stillbirths can be caused by near-term situations such as ketosis, milk fever, selenium deficiency and dystocia or several infectious causes.
Infectious Causes of Abortions
There are many potential causes of abortions in small ruminants, but infectious diseases are the main culprits. Many of these diseases are transmissible to humans (particularly pregnant women), so precautions should be taken when handling animals, especially those that are giving birth and/or appear ill. Wear protective clothing and gloves and dispose of contaminated materials and bedding carefully; wash hands thoroughly. Do not consume unpasteurized dairy products.
Enzootic abortion is caused by a pathogen called Chlamydophila abortus (Chlamydia psittaci serotype 1). This bacteria causes weak lambs, stillbirths and high rates of late-term abortions, especially in first-time dams. Lambs that live may appear healthy or they may show signs of pneumonia. Adult dams do not show any signs of illness before aborting. The organism is spread through contact with aborted tissues, fluids and dead fetuses as well as the feces and respiratory discharges of infected carriers. Most infected animals mount an immune response to the organism and only abort once, but remain carriers and periodically shed the organism. Infected rams can spread the disease venereally.
Prevent enzootic abortion by keeping a closed flock or purchasing only maiden females; administering specific antibiotics before lambing based on veterinary recommendations; isolating aborting ewes; removing aborted tissues and disinfecting areas where abortions have occurred; and vaccinating pregnant ewes before annual lambing.
For goats, the above is applicable with the following additions: abortions are generally late term but can occur at any point during gestation; abortions may occur along with pneumonia, conjunctivitis, retained placentas and arthritis; goats that abort are probably immune for life but their ability to shed the organism is unknown; and there is no vaccine approved for use in goats.
Vibrionic abortion is caused by Campylobacter fetus or Campylobacter jejuni, organisms that live in intestinal tract. The disease is much more common in sheep than goats. Small ruminant vibrio is spread by ingestion of the organism and often introduced to a farm through purchase of an infected carrier animal. The disease is also spread through contact with aborted fluids and tissues and contaminated fomites--things such as boots, birds and equipment that move the organism from place to place. Abortions occur in the last one to two months of pregnancy and rates can range from 20 to 90% in a herd/flock during an outbreak. In addition to abortions, stillborn and weak lambs can occur. Although dams usually do not show signs of illness with vibrio, they can get diarrhea or become ill and/or die from complications secondary to miscarriages (e.g. uterine infections). After aborting, most dams are clear of the disease and have lifelong immunity. However, some remain carriers and spread the organism in their manure, contaminating the premises.
Medication can be effective during an abortion storm and a pre-breeding vaccine is available for prevention. Contact your veterinarian for more information.
Toxoplasma gondii, a parasitic disease of cats, can cause abortion in sheep and goats that ingest feed or water contaminated with infected cat feces. Losses range from 5 to 50% of pregnancies. This disease can affect any stage of pregnancy, so reproductive problems include EED, mummification, abortions, stillbirths and weak lambs. Some dams may demonstrate signs of nervous system involvement and die.
No vaccine is available to prevent this disease, but some of the coccidia prevention feed additives have shown some preventative effects when used at extra-label dosages; check with your veterinarian for more details. Prevention should also include keeping feed and water free from cat feces. Cats can be trained to use a litter box in a barn; this designated waste site should be cleaned and maintained regularly to encourage use. Kittens are more likely to shed the causative organism in their feces so their presence in the environment of pregnant sheep and goats should be controlled. Ewes and does will develop immunity if they are exposed to the disease so if exposure is inevitable, arrange to have it occur before animals are bred.
Several species of Salmonella can cause abortion if ingested by a pregnant doe or ewe, especially if a large number of organisms are ingested and the dam is ill or stressed. Abortions tend to be late in gestation and rates can be up to 70% of pregnancies. Affected dams are often ill with a fever and diarrhea and may die from complications such as blood poisoning. The disease can be spread to healthy herdmates, including neonates. It is also a human health concern.
Coxiella burnetii Abortion
Coxiella burnetii causes Q Fever in humans and can be transmitted through non-pasteurized milk. It can cause late-term abortions, stillbirths and weak lambs and kids. It is much more common in goats than sheep.
Several species of the bacteria Leptosira can cause abortion in goats; sheep are more resistant to this disease. Some affected goats can show jaundice, dark urine, anemia and have a fever; others will appear unaffected. Abortions can occur any time during gestation.
Brucella melitensis and B. abortus can cause abortions in sheep and goats; B. ovis can cause stillbirths, late-term abortions and weak lambs. Affected dams may be lame and have mastitis; they are affected for life and shed the organism in their milk. This disease has important human health implications and is another reason not to ingest unpasteurized dairy products.
Disease caused by Listeria monocytogenes is more common in goats than sheep and can cause abortions; those in ewes tend to be in late pregnancy. Signs of illness are usually not seen in does before they abort. There is no vaccine for prevention but specific antibiotics can be given during a herd outbreak to prevent new abortions.
Border disease in sheep is cause by a virus similar to the bovine viral diarrhea virus. It can cause EED, abortions at any stage, weak lambs and lambs born with defects such as muscle tremors, hairy coats and small size. No vaccine is approved for use in sheep.
Caprine Herpesvirus 1 can cause occasional late term abortion outbreaks in goats with or without other signs of illness. Signs of disease can include inflammation of urogenital mucous membranes, diarrhea in kids and respiratory disease in adults. Multiple diagnostic methods are available. Goats can become carriers and shed intermittently when stressed.
Other Infectious Causes
The Cache Valley virus can cause abortions, stillbirths, infertility and birth defects in the nervous and musculoskeletal systems of lambs. The Bluetongue virus can also cause abortion and birth defects in sheep. Neospora caninum is a parasite of dogs that can cause abortions in sheep.
Significant deficiencies of any essential nutrient (water, protein, energy, vitamins and minerals) could result in poor fetal health. For example, White Muscle Disease is common in many areas of the country. It is caused by low selenium levels in soils and feeds grown in those soils. Lambs and kids born to selenium-deficient dams may be stillborn, small or weak. Pregnant dams can be given supplemental injections of Vitamin E/Selenium and neonates can be given the injections at birth and as needed thereafter, followed by a dietary mineral supplement. See your veterinarian for more information.
Pregnancy toxemia can occur in the last six weeks of pregnancy in goats and sheep carrying more than one fetus. If not fed properly, the dam can go into negative energy balance as the growing fetuses demand more nutrition from their mother, whose rumen has less and less room to hold food. The process of mobilizing the dam’s fat stores releases toxic ketone bodies, which can make the dam anorexic and kill the fetuses. Prevention is focused on increasing energy in the dam’s ration as she progresses through pregnancy.
Milk fever is not very common in sheep and goats, but if left untreated can result in abortions, stillborns or weak neonates. Signs in near-term dams include recumbency, weakness, hypothermia, depression and muscle tremors, all due to abnormally low blood calcium. Treatment involves administering calcium by mouth, under the skin or intravenously with extreme caution. Prevention involves careful attention to pregnant animals’ mineral status; work with your veterinarian or Extension educator to develop the proper ration for all stages of production in your flock/herd.
Miscellaneous other causes of abortion in small ruminants can include plant toxins or other poisons, mycotoxins from moldy feed, nitrates, high fevers, heat stress, fighting, rough handling and some medications. Genetic causes are probably common but difficult to identify.
Although a definitive diagnosis is made in less than 50% of abortions, a diagnostic workup is always warranted when abortion rates rise above those typical for a farm. Working closely with your veterinarian and diagnostic laboratory will give the best chance of a definitive diagnosis. Your veterinarian and the lab will need to know the history of your herd/flock and the disease outbreak, vaccinations given, recent additions to the herd, signs of illness and so on. The fresher the tissues submitted to the lab, the greater the likelihood an infectious disease will be identified if it is present. Your veterinarian will advise you on what tissues to submit or will collect and submit him/herself. Keep samples chilled, not frozen, until they can be sent to the lab. Use plastic gloves and protective eyewear when handling any aborted tissues. Blood from the affected dam(s) can be submitted for viral isolation and other tests; antibody levels in serum taken at the time of the miscarriage and a few weeks later can be compared for evidence of an active disease process.
In the event of an abortion outbreak, identify animals that have aborted and isolate them from the rest of the herd/flock. Bury or burn aborted materials not submitted to the diagnostic lab; also remove all bedding from the abortion area, disinfect and leave vacant for as long as possible. Ask your veterinarian about feeding medications to the flock/herd while awaiting results from the laboratory. Keep personal safety in mind, always wearing protective clothing and washing thoroughly after handling animals or equipment.
Pre-breeding vaccines for Chlamydia and Vibrio are essential after either of these diseases has been diagnosed on a farm. Other prevention measures include not feeding animals directly on the ground or allowing them to drink stagnant water; preventing feed contamination; employing strict sanitation measures; keeping a closed herd/flock or only purchasing from known clean sources, then keeping these animals separate until after giving birth; discouraging cats from defecating in hay and grain; minimizing stress to animals by providing adequate nutrition, feeder space and room; keeping bred doelings and ewe lambs separate from mature does and sheep; and not mixing bedding between birthing pens and other animal holding pens.
Abortion storms can turn the most enjoyable part of the livestock production cycle into a nightmare. Recognizing the problem quickly, involving your veterinarian immediately, pursuing diagnostic testing and implementing treatment and sanitation steps can stop some storms in their tracks, minimizing their potentially devastating impact on your farm.
For More Information