Abortion in sows can have multiple causes of non-infectious and infectious origin that must be determined to control them in time.

Sows are a species of animal characterized by having a relatively rapid gestational period and being multiparous. The sow’s gestation lasts an average of 115 days and can have a litter of piglets averaging of more than 14 animals at farrowing.

During gestation, several risks can jeopardize the viability of the sow. There are infectious and non-infectious causes that can lead to the death of embryos or fetuses, as well as their premature expulsion. For this reason, it is very useful for the swine farm to determine the causes of abortion and implement prevention strategies as soon as possible.

Gestational loss in sows

In the gestation of the sow, there can be multiple pathological outcomes that lead to a lower number of piglets born alive. These losses occur at different times of gestation and for various causes. Abortion is one of the most important, but it is of great relevance to know the other gestational losses that can occur in the sow.

Embryonic death

It occurs during the first days of gestation where the embryos die before implanting in the uterus.

Fetal death

It can be of infectious or non-infectious origin, for genetic reasons (chromosomal or congenital), intoxications, stress, among others. It occurs when the fetus has finished developing and is in the growth phase.

Fetal mummies

Fetuses may die in utero and dehydrate to the point of becoming mummies. These mummies are not always expelled or aborted and can lead to subsequent reproductive problems.

Fetal mummification

In cases where fetal mummies become contaminated with bacteria, this material begins a process of putrefaction where the tissues dissolve and there is a severe inflammatory response. This can lead to endometritis or pyometra in the sow.

Abortion

Abortion is the expulsion of fetuses before the proper time of parturition and has multiple causes.

Stillbirth

Stillbirths are piglets that completed their development correctly but died in peripartum.

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Infectious causes of abortion in sows

Infectious causes include pathogens of viral and bacterial origin present in most regions of the world.

Porcine parvovirus

This disease of viral origin is present in most regions of the world. Infected sows acquire permanent immunity. However, first farrowing sows are affected. If infected before the first month of pregnancy, there is embryonic mortality. In the second third of pregnancy, there is fetal death and mummification. Fetuses infected in the last third of gestation are born with immunity and overcome the infection.

Porcine Reproductive and Respiratory Syndrome (PRRS)

This syndrome is caused by an arterivirus and is of great importance worldwide. Abortions occur at the end of gestation generating pigs with autolysis, weak piglets, or piglets that are born alive and die later due to respiratory complications. Pregnant sows have respiratory signs and fever near abortion. The characteristic of PRRS is umbilical cord hemorrhage.

Aujeszky’s disease

It is an infection of porcine herpesvirus type. It is also called Pseudorabies because of the rabies-like neurological signs it causes. Infected animals become carriers and the disease is activated by latency. It can cause embryonic death, mummification, or abortion depending on the time of infection in the sow.

Swine circovirus

This disease is caused by a ubiquitous virus called porcine circovirus type 2. Abortions can occur in late gestation and increase the number of stillbirths, fetal mummies, and weak piglets. Naturally exposed animals become immune.

Swine Fever (African and Classical)

These viral diseases are eradicated in some parts of the world but remain a major problem in most parts of the world. Abortion is a consequence of this disease, as well as stillbirths or fetal mummies. It is controlled by vaccination. It can cause persistently infected animals.

Brucellosis

This disease is caused by the bacterium Brucella suis. Sows become infected orally and cause abortions at any stage of gestation. There are not always observable clinical signs, but it can cause endometritis and infection of the fetus. It is a zoonotic disease of great importance and is controlled by vaccination and slaughter since there are no treatments.

Leptospirosis

This zoonotic disease caused by Leptospira interrogans includes many serovars causing reproductive problems. Most cases in adult sows are asymptomatic. Abortion may occur 1 to 4 weeks after infection and fetuses undergo autolysis. In addition, it can cause fetal mummies, fetal maceration, stillbirths, and persistently infected animals.

Mycotoxins

Mycotoxins are dangerous toxic metabolites that originate in sow feed and can cause abortions. Among these are aflatoxins, fumonisins, zearalenone, deoxynivalenol, or ergot alkaloids. Abortions can occur early in gestation or cause mummification of piglets.

Other bacterial infections

Some bacteria are associated with cases of abortion in sows.

– Staphylococcus aureus

– Streptococcus spp.

– Erysipelothrix rhusiopathiae

– Salmonella spp.

– Pasteurella multocida

– Trueperella pyogenes

– Listeria monocytogenes

– Escherichia coli

Non-infectious causes of swine abortion

In addition to bacterial or viral causes, there are non-infectious causes present in the feed or environment that can lead to abortion in sows.

Carbon monoxide poisoning

Signs of this poisoning are difficult to find. Tissues analyzed during fetal necropsy may have an intense red color. This affects the proper oxygenation of the tissues and their function, causing death within hours.

Feed origin

The feed supplied to pregnant sows must be balanced and in excellent condition. Otherwise, it may cause malnutrition or contain vitamin antagonists that prevent their absorption and functioning. In addition, they may contain phytotoxins, cause allergies or chronic intoxications.

Environmental contaminants

Mycotoxins in food raw materials have a synergistic effect together with molecules called polychlorinated biphenyls present in many products (paint, pesticides, machinery fluids). The latter have estrogen-like behavior and bind to their receptors, altering the hormonal cycles of sows.

Heat stress

Heat stress in sows has serious consequences on their physiology, including abortion. The environmental temperature of the pregnant sow herd should be monitored and controlled according to her comfort.

Diagnosis of abortion in sows

Importance of sampling

The diagnosis of abortion in sows depends to a large extent on the quality of the samples taken. Therefore, these samples should be taken from the correct organs depending on the presumptive diagnosis and stored and shipped with the recommended methods. It is recommended that reference laboratories be contacted to indicate the proper procedure for sample collection and shipment. On the other hand, it is recognized that a history of the herd health status is of great help, as well as sending as much information as possible (affected lots, number of animals, age, vaccination, among others).

Necropsy in swine

For the diagnosis of abortion in sows, it is very useful to send tissues to determine the cause. The most useful organs are the placenta and fetuses obtained from the abortion, refrigerated and not frozen. These tissues are subjected to macroscopic investigation to observe lesions that can provide a guide to the diagnosis, but samples are usually taken for specific laboratory analysis.

Histopathology

Tissues collected from necropsy are processed for observation under the microscope to approach the diagnosis.

Bacteriology

Bacteriological studies allow determining the etiology of abortion in sows. This technique allows finding bacteria such as Actinobacullus, Streptococcus, Erysipelothrix, Trueperella pyogenes, Pasteurella, Salmonella, Bacillus, E. coli, among others. Some of the useful tissues for this method are fetal lungs, stomachs, and placenta.

Virology

Viruses causing an abortion in sows can be diagnosed by viral isolation or immunofluorescence. This allows determining viruses such as transmissible gastroenteritis, Pseudorabies virus (Aujeszky), swine influenza, porcine circovirus, porcine parvovirus, PRRS, among others.

Serology

The measurement of antibodies is a useful diagnostic tool when performed in fetal fluids. If the antibodies are elevated, it is indicative of infectious disease as a cause of abortion. In the case of the sow, the analysis must be careful, and vaccination should be considered as a factor that alters the results.

Abortion prevention strategies

Strategies for the prevention of abortion in sows are focused on all causes, whether infectious or non-infectious.

• Avoid moving sows during the first 40 days of gestation as it generates stress that can induce embryonic mortality.
• Do not inseminate sows with low body condition since they will have difficulties carrying to term the gestation due to their catabolic state.
• Perform a physicochemical and bacteriological analysis of water and feed to rule out food poisoning by salts, mycotoxins, or bacteria.
• Optimize ventilation and good management of environmental temperature to avoid heat stress.
• Establish a sanitary plan that includes immunization against viruses and bacteria causing abortions if available in the country.
• Use of mycotoxin binders to prevent the pathogenic effect of mycotoxins through consumption of contaminated feed. Alquerfeed Antitox is a mycotoxin binder based on Silicoglycidol. This molecule of natural origin prevents the absorption of mycotoxins and their irritant effect on the intestinal mucosa. In addition, it does not affect the absorption of vitamins, enzymes, amino acids, or drugs.
• The use of the natural immunostimulant Alquernat Inmuplus strengthens the pigs’ defense system, both specific and non-specific immunity. This product is very useful in young animals because their immune system is still immature and in adults whose breed is characterized by rapid growth or high prolificacy. On the other hand, this product of natural origin improves the response to vaccination and is an excellent complement to pharmacological treatments. Thus, it is emerging as an important option in strategies to prevent abortion in sows.

Conclusions

In swine farming, pregnant sows constitute one of the pillars of production. These females are exposed to infectious and non-infectious factors that can generate a gestational loss.

Gestational loss can occur at different times causing embryonic death, fetal death, mummies, stillbirths, weak piglets, or abortions. Infectious causes include viruses such as PRRS, Circovirus, Parvovirus, and Pseudorabies, as well as Brucella and Leptospira bacteria.

On the other hand, there are non-infectious causes related to management, feeding, and environmental factors that can lead to abortion in sows.  Diagnostic methods are available to determine the cause of abortion such as necropsy, histopathology, virology, or serology tests.

Finally, various prevention strategies are recommended to control all causes of abortion and to reduce the economic and productive losses of the herd.