Any time a sow farrows prematurely, there is the fear that additional litters will be lost. An abortion rate of less than 2 percent is considered an acceptable level in most herds. Premature farrowing usually results from nutritional, genetic or environmental stresses, but the exact cause is often unknown. This publication addresses several infectious causes of infertility and abortion in sows along with some preventive measures

Floss, Jeanette L.

Tubbs, Roderick C.

University of Missouri: MOspace

University of Missouri ExtensionG2315, Reviewed October 1993Infectious Causes of Infertility in SowsJeanette L. FlossCollege of Veterinary MedicineRoderick C. TubbsSwine veterinarianCommercial Agriculture ProgramAny time a sow farrows prematurely, there is the fear that additional litters will be lost. An abortion rate ofless than 2 percent is considered an acceptable level in most herds. Premature farrowing usually results fromnutritional, genetic or environmental stresses, but the exact cause is often unknown.Abortion is the most dramatic expression of production loss. When the incidence increases for a given herd,an infectious agent is usually suspected. This increase may follow the addition of replacement animals or themingling of previously isolated groups of animals. Approximately 38 percent of diagnosed abortions areattributed to infectious causes.The stage of gestation during which the sow and/or fetuses become infected will determine the litter's abilityto survive. In some cases the infectious agent will directly affect developing fetuses and placentas, causingfetal compromise and death.Any severe illness in a pregnant sow may result in fetal death due to a disruption in the normal uterineenvironment. One, several or all fetuses in a litter may be lost. If fetal compromise occurs at less than 35 daysof gestation, fetuses may be reabsorbed. If infection occurs between 35 and 70 days of gestation, fetalmummification occurs. If infection occurs after 70 days of gestation, pigs may be delivered weak or dead.This publication addresses several infectious causes of infertility and abortion in sows along with somepreventive measures.Bacterial infectionsBacteria gain access to the uterus through the open cervix at farrowing, but usually are eliminated before theyare able to establish an infection. Sows will have a vaginal discharge for 1 to 3 days after farrowing. Thisdischarge is normal, is not foul smelling and is not associated with clinical illness in the sow or pigs.However, if a sow farrows in an environment contaminated with excessive fecal material or the delivery isassisted in an unsanitary fashion, metritis may develop. This is the most severe form of infection in the uterus.The uterus fills with large amounts of malodorous fluid and decomposing fetal membranes. The sow willdevelop a fever, be ill and possibly die as a result of bacterial toxins. Her pigs may demonstrate signs ofmalnourishment. This condition is seen within days of farrowing. If the sow recovers, her fertility during thenext breeding will be reduced.Endometritis or inflammation of the lining of the uterus is less severe clinically, but possibly more importanteconomically. Bacterial infections of the reproductive tract may result in conception failure and/or earlyembryonic deaths. Bacteria gain entrance to the uterus during estrus and breeding because the cervix relaxesG2315 Infectious Causes of Infertility in Sows | University of Missouri Ex... http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...1 of 6 3/15/2010 11:34 AMat this time. An increased return-to-service rate may be the only indication that a problem exists. Returnintervals may be normal or prolonged.Inflammation of the endometrium is not compatible with the survival of embryos and the pregnancy will beterminated. These animals are often clinically normal or they may have a low-grade fever. A mild vaginaldischarge may be seen around the time of the next expected heat. Gilts that are housed in overcrowdedconditions may also develop endometritis.Vaginitis will also cause a vaginal discharge. Fertility may not be reduced unless bacteria gain entrance to theuterus at breeding. Gilts and sows that have been exposed to high levels of the mycotoxin zearalenone in thediet will develop vaginitis and a discharge. The estrogenic properties of this compound will prevent theseanimals from cycling normally.A diet high in calcium or phosphorous may result in the formation of salts in the urine leading to a white,chalky fluid which is seen at the vulva. This should not be confused with infection, although infections of theurinary tract may cause vaginal discharges. Adequate water intake helps to prevent infection by encouragingfrequent urination and mechanical flushing of the urinary tract.The bacteria that cause these urinary and reproductive tract infections can be found within the tracts and/orin the environment. When the tracts are contaminated and the defense mechanisms are overloaded, infectionresults. The most effective means of preventing this is to provide a clean environment (proper waste removal)and a sufficient source of fresh water.LeptospirosisA large number of Leptospira organisms are known to infect swine. In most herds that have already beenexposed, few clinical cases of disease will be found.Leptospira bacteria prefer the kidney and are shed in the urine. Contact with contaminated urine is the mostcommon means of spreading the infection to other animals. Leptospira also will localize in the pregnantuterus. If susceptible breeding animals become infected, leptospirosis may lead to abortions, stillbirths or thebirth of weak neonates.Several serovars of Leptospira interrogans have been found to infect swine. Pomona is most commonlyinvolved in swine infertility. Bratislava also has been found to persist in the oviducts and uterus ofnon-pregnant females and in the upper genital tract of boars contributing to infertility. It is possible that thisinfection could be spread during mating. At the present time, however, bratislava infection has not beenlinked to clinical outbreaks on a wide scale in the U.S.Vaccines are available for leptospirosis. However, the immunity they provide is usually short-lived. Breedinganimals should be vaccinated at least twice a year and up to four times a year in infected herds. Vaccinationsshould be given prior to breeding. Antibiotics will help reduce the incidence of disease but cannot completelyeliminate it from an infected herd. Rodents and local wildlife may also be infected and contribute to thespread of leptospirosis. Management practices that eliminate the rodent population and prevent urinecontamination of feed and water will contribute a great deal to controlling infection. During an outbreak,clinically ill animals should be treated and in-contact animals should be vaccinated.BrucellosisBrucellosis in swine is caused by Brucella suis. Brucella organisms are also infectious to humans, but due tofederal eradication programs very few cases are reported in people or livestock. Brucellosis is spread byG2315 Infectious Causes of Infertility in Sows | University of Missouri Ex... http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...2 of 6 3/15/2010 11:34 AMdirect contact with infected tissues, primarily aborted fetuses and membranes. Boars can develop a persistentinfection and shed bacteria in the semen, which contributes to the spread of this disease. Females that becomeinfected at breeding may abort at any stage of gestation.Antibiotics are of little value in treating brucellosis. The prevalence of swine brucellosis has been reduced tothe point that vaccination is not practical. Management practices for maintaining a brucellosis-free herd statusare encouraged. The human health risks of brucellosis should always be considered when handling anyaborted fetuses or fetal membranes.Porcine parvovirusFew animals exhibit clinical illness as a result of porcine parvovirus (PPV) infection. This virus is found inmost swine herds, but previously exposed animals develop immunity.Porcine parvovirus will cross the placenta and infect developing fetuses. Non-immune females that becomeinfected during the first half of gestation will usually have several mummified fetuses at farrowing. Gilts areaffected much more often than sows.Infertility, stillbirths, neonatal deaths and delivery of weak pigs may follow infection during pregnancy.Abortions resulting from PPV infection are uncommon. If infection occurs late in gestation, fetuses usuallywill survive.Because PPV is widespread in swine herds, all gilts should be naturally exposed or vaccinated at least 30 daysprior to breeding. Inactivated as well as modified live vaccines are available and should be administered underthe direction of a licensed veterinarian. There is no treatment for PPV-induced infertility, but animals that arenaturally infected are often immune for life.Porcine enterovirusesLike porcine parvovirus, porcine enteroviruses are present in most swine herds but often do not cause clinicalillness. Enteroviruses have been associated with central nervous system disease (polioencephalitis), diarrheaand pneumonia. They may also produce non-specific fetal losses resembling those seen with PPV infection.Viruses cross the placenta, therefore pregnant gilts and sows may deliver stillborn pigs and mummies, deliverfewer pigs per litter or fail to farrow. Abortions are rare.There is no vaccine available for protection against reproductive losses resulting from enterovirus infections.The best preventive practice is to make sure gilts have been exposed to the fecal material of other herdanimals, especially older sows, at least one month prior to breeding. As with PPV there is no treatment forenterovirus infection. However, subsequent fertility does not appear to be affected.PseudorabiesAbortions resulting from pseudorabies virus (PRV) infections typically follow a period of fever andrespiratory disease in pregnant gilts and sows. If susceptible females become infected early in gestation,fetuses may be resorbed. Approximately 20 percent of females that become infected late in gestation willabort. Pigs that are delivered alive are weak and often do not survive more than a day or two. Other signs ofdisease in a recently infected herd include pneumonia in grower/finisher pigs and nervous system disease anddeath in suckling and newly weaned pigs. Endemically (chronically) infected herds may show no clinical signsother than an increased susceptibility to respiratory disease in growing and finishing pigs.G2315 Infectious Causes of Infertility in Sows | University of Missouri Ex... http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...3 of 6 3/15/2010 11:34 AMVaccines for PRV are available. These do not prevent clinical illness if animals become infected, but theyreduce the severity of the disease and its spread within the herd. Vaccinations should be performed by alicensed veterinarian and in association with the state regulatory recommendations for the eradication ofPRV.PRRS/SIRSIn the late 1980s, many swine herds experienced a large number of abortions. An increased incidence ofstillbirths and mummies followed the abortion storms. Survival rates were poor for pigs born alive.Pneumonia, affecting pigs of all ages, was also reported in these herds. Many recovering sows experiencedperiods of infertility lasting for varying lengths of time. Recently an RNA virus has been isolated as thecausative agent. This disease process, once identified as Mystery Pig Disease, is now known as PorcineReproductive and Respiratory Syndrome (PRRS) or Swine Infertility and Respiratory Syndrome (SIRS).Newly infected herds followed the disease pattern described above. More recently PRRS has been associatedwith poor doers in the nursery and decreased farrowing rates. In addition, conception rates and the number ofanimals bred have decreased. Near farrowing, sows may develop a fever and go off feed.Because there is no specific treatment for PRRS, supportive therapy should be provided to clinically illanimals. Medications to reduce fever and to encourage animals to resume eating are beneficial. Presently, novaccine is available for the control of PRRS/SIRS. Purchasing animals from herds that have not beenexposed, isolation of new animals for at least 30 days and strict control of animal movement within the herdwill help to minimize the spread of this disease.SummaryAbnormal vaginal discharges must be distinguished from normal postpartum discharges and urinary sedimentsin order for affected animals to be properly managed. Discharges resulting from reproductive tract infectionsgenerally are associated with other reproductive events such as farrowing (metritis) and estrus or breeding(endometritis). Discharges associated with vaginitis and urinary tract infections usually do not follow thereproductive cycle. Milder cases can be treated with antibiotics, but persistently infected animals should beculled.Porcine parvovirus or enterovirus should be suspected when the incidence of mummified fetuses increases,particularly in gilts not previously exposed. Respiratory distress accompanied by high fever and followed byabortions may indicate a pseudorabies or PRRS infection in a susceptible herd. Abortions resulting frombrucellosis are uncommon but leptospirosis should be considered in areas where it is prevalent.Infectious reproductive problems are best controlled by stringent preventive management practices. All giltsshould be exposed prior to breeding to older sows in herds with PPV and PEV. Once infected, gilts willdevelop a life-long immunity and subsequent fertility is good.Vaccines are available for PPV, PRV and leptospirosis. These should be administered at least 30 days prior tobreeding gilts and repeated as necessary in high-risk areas (leptospirosis). Herds are best protected from PRVand PRRS by raising replacement gilts or obtaining them only from herds that are free of these diseases. Newadditions should be isolated from the rest of the herd for the first 30 days.Sanitary maintenance should include adequate waste removal, sufficient housing space and the prevention offeed and water contamination. The combination of all these management practices will reduce productionlosses resulting from infectious causes.G2315 Infectious Causes of Infertility in Sows | University of Missouri Ex... http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...4 of 6 3/15/2010 11:34 AMTable 1Infectious causes of infertilityMixed bacterial infections Clinical signsIncreased return-to-service. Mild to profuse vaginal discharges. Sows with metritis will have afever and go off feed.Preventive measuresDo not house gilts or sows in overcrowded, unsanitary conditions. Provide ample amounts offresh water.CommentsA discharge for one to three days after farrowing is normal.Leptospirosis interroganspomonaClinical signsFew clinical cases in previously exposed herd. Susceptible breeding females may abort ordeliver weak or dead pigs.Preventive measuresVaccinate breeding animals two to four times each year. Protect feed and water from urinecontamination.CommentsRodent numbers should be controlled because they also contribute to the spread of thisdisease.Brucella suis Clinical signsAbortions during any stage of pregnancy.Preventive measuresPrompt removal of all aborted tissues. Routine testing for maintenance of brucellosis-freeherd.CommentsPotential for human infection.Porcine parvovirus Clinical signsDelivery of mummified pigs. Stillbirths, neonatal deaths and infertility are possible. Abortionsare rare.Preventive measuresVaccinate or expose gilts to infection 30 days prior to breeding.CommentsPreviously infected animals develop a life-long immunity.Porcine enteroviruses Clinical signsResembles porcine parvovirus. Abortions are rare.Preventive measuresExpose gilts to fecal material from older sows prior to breeding.CommentsNo vaccine is available.Pseudorabies virus Clinical signsAbortions may follow fever and respiratory disease in susceptible gilts and sows. Live-bornpigs are weak. Pneumonia in growing pigs.Preventive measuresVaccination will reduce the severity of clinical disease. Participation in the federal eradicationprogram.G2315 Infectious Causes of Infertility in Sows | University of Missouri Ex... http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...5 of 6 3/15/2010 11:34 AMCommentsVaccination requires the approval of the state veterinarian.PRRS/SIRS virus Clinical signsNew herds experience an increase in abortions, stillbirths and mummies. Pneumonia in pigs ofall ages. Reduced fertility in recovered sows.Preventive measuresNew animals should be purchased from unexposed herds and quarantined for at least 30 days.CommentsNo vaccine is available.G2315, reviewed October 1993Related MU Extension publicationsG2340, Biosecurity for Today’s Swine Operationhttp://extension.missouri.edu/publications/DisplayPub.aspx?P=G2340G2508, Herd Health Programs for Swine Seedstock Productionhttp://extension.missouri.edu/publications/DisplayPub.aspx?P=G2508MM102, Missouri Swine Enterprise Manual CDhttp://extension.missouri.edu/publications/DisplayPub.aspx?P=MM102Order publications online at http://extension.missouri.edu/explore/shop/ or call toll-free 800-292-0969.G2315 Infectious Causes of Infertility in Sows | University of Missouri Ex... http://extension.missouri.edu/publications/DisplayPrinterFriendlyPub.asp...6 of 6 3/15/2010 11:34 AM

Infectious causes of infertility in sows (1993)

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