Glen W. Almond
Department of Food Animal and Equine Medicine
College of Veterinary Medicine
North Carolina State University
Raleigh, NC 27606


Most producers have observed the occasional sow with a vulvar discharge. These individual cases rarely represent a major concern. In contrast, some start-up units or farms with large numbers of gilts are often faced with numerous bred (or open) animals (5-10% of a breeding group) affected with vulvar discharges. These epizootics or herd outbreaks evidently have occured with increased frequency. It is not clear whether the swine industry is experiencing a "new disease problem" or the that confinement facilities (ie. breeding/ gestation crates) permit producers ot observe vulvar discharges. Furthermore, it has been difficult to estimate the precise number of abnormal versus normal vulvar discharges in these herd outbreaks.

Vulvar discharges have created a diagnostic problem for producers and veterinarians. Whereas some vulvar discharges are indicative of normal physiological events, other discharges are pathological and interfere with fertility and conception (Table 1) or involve the health of the affected animal. Although abnromal discharges originate from either the urinary or reproductive tracts (Figure 1), this paper will focus on vulvar discharges that originate from the reproductive tract. In addition, this brief reveiw is intended to (1) improve producers' understanding of vulvar discharges and (2) challenge our traditional concepts of treatments and prognosis of affected animals.

Figure 1. Anatomy of the sow's urogenital tract and possible sites of infection.

Normal Vulvar Discharges

Postparturient (post-farrowing) discharges and peri-estrous discharges are considered normal vulvar discharges in the sow. Discharges following farrowing usually represent the sow's attempts to clear placental remnants and debris from the uterus. Although most post-farrowing discharges are normal, producers must carefully observe sows for infectious or toxic metritis or retained pigs.

The hormone changes, associated with onset of estrus and ovulation, contribute to vulvar discharges in per-estrous animals. These changes result in the production of mucous to mucopurulent vulvar discharges (clear to yellow/brown color) at the time of esturs. We have noted that many animals will continue to discharge for up to 7 days (sometimes more) after estrus and mating. The discharge contains mucus, vaginal epithelial cells, semen, white blood cells, occasional red blood cells or any combination of these cells. The quantity of these "normal" discharges varies form sow to sow and the fertility of these animals is rarely affected. Similarly, a mucopurulent vulvar discharge often is noted in pregnant sows in the last 2-3 weeks of gestation. The elevated serum estrogen concentrations during late pregnancy and during estrus induce mucus production and cellular changes in the vulvo-vaginal membrances, thereby, resulting in a "sterile" discharge.

Table 1. Types of vulvar discharges in female pigs.

Normal Physiologic Discharge Pathologic Discharge
Genital Tract Genital Tract
Estrus Discharge
Service Discharge
Post-farrowing Discharge
Cervical/Seminal Plug
Vulvar Abscess
Blood via trauma
Urinary Tract Urinary Tract
Urine Crystalluria/urolithiasis

Abnormal Discharges

Blood: It is common to note the presence of fresh blood on the vulva of sows and gilts. Vulvar lacerations are often the result of biting by sows, particularly in pen housing. In contrast, the swollen vulva of a sow during estrus is subject to trauma by breeding or gestation crates. Careful inspection of the crates usually reveals sharp or abrasive edges.

Another common casue of vulvar lacerations and bleeding is trauma during mating. Blood is not spermicidal but it is a good idea to implement handmating procedures that reduce the likelihood of breed-inflicted vulvar lesions since they may indirectly affect reproductive processes.

Post-breeding Purulent Discharges: The presence of a purulent vulvar discharge at 16 to 20 days after breeding (or estrus) typically is indicative of a uterine infection (metritis or endometritis). Affected animals invariably return to estrus and consequently, this type of discharge represents a major concern to the breeding manager. Presently, we do not know the precise casue of uterine infections; however, the causative agent(s) likely enter the uterus during estrus, either passively or they are introduced by the boar during mating. Several bacterial species have been isolated from these infected uteri, inclucing, E. Coli, Streptococci sp., and a variety of others. Unfortunately, ivestigators have not identified a specific pathogen responsible for all discharges. Evaluation of the reproductive tracts at slaughter has yielded limited information because the animals have either resolved the infection or overgrowth of opportunistic bacteria has occured. A recent study indicated that sows bred late during estrus (often the third mating) are susceptible to discharge problems; however, this does not completely explain the problems observed in start-up units.

Treatment: Numerous treatment protocols have been attempted to resolve discharging sow problems: their success remains very dubious. The use of medicated feed or injectable antibiotics are common treatments. Since we do not know the precise pathogens and the cost- effectiveness of antibiotic treatments, it is often difficult to justify such treatments. Infusion of the boar's prepuce has been a common therapy; however, the prepuce of a boar is rapidly re-infected and thus, offers short-term therapy.

Prognosis: The vast majority of discharging sows return to estrus shortly after the initial appearance of the discharge. Do not bother to breed these animals at this time. Perhaps the most appropriate approach is to allow the animals to recycle one more time. If they fail to discharge a second time, it is evident that their conception rate will be similar to a repeat breeder. The other option is to cull any animal with a discharge at 16-20 days after breeding. Obviously, there is not a clear solution to the problem.

Some producers and breeding managers consider the "discharging sow" as a major reason for low conception and farrowing rates. Unfortunately, the discharging sow may mask the actual problem of suboptimal breeding house management. Therefore, it is important to keep accurate records on discharging sows. These records should help classify the type of discharge (normal vs abnormal), quantify the precise number of animals and to ensure that you are not treating or culling normal animals. The swine medicine group at NCSU currently are conducting additional studies of the discharging sow problem.