VULVAR DISCHARGES IN FEMALE PIGS: NATURAL MATINGS VERSUS ARTIFICIAL INSEMINATION

Introduction

Most producers observe the occasional sow with a vulvar discharge. These individual cases rarely represent a major concern. In contrast, some producers observe numerous bred (or open) animals (5-10% of a breeding group) with vulvar discharges. Diagnostic evaluation of vulvar discharges is challenging. Some vulvar discharges are indicative of normal physiological events. Other discharges are pathological and interfere with fertility and conception (Table 1) or affect the health of the affected animal. Abnormal discharges originate from either the urinary or the reproductive tracts.

The boar was generally assumed the cause of all discharges; however, the results of various studies showed that other factors are the primary causes of discharges. We previously believed that artificial insemination (AI) would eliminate problems with vulvar discharges. Unfortunately, discharges continue to hamper reproductive performance of sow herds. This paper will review the common causes of a discharging sow and consider the relevance of AI on this nagging problem.

Normal Vulvar Discharges

Postparturient 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. Most postfarrowing discharges are normal; however, producers must carefully observe sows for infectious or toxic metritis or retained pigs.

Hormone changes, associated with the onset of estrus and ovulation, contribute to vulvar discharges in peri-estrous animals. These changes induce production of mucous to mucopurulent vulvar discharges at the time of estrus. Similarly, a mucopurulent vulvar discharge often is noted in pregnant sows in the last 2-3 weeks of gestation. Some animals will continue to discharge for up to 7 days after estrus and mating. The quantity of these "normal" discharges varies from sow to sow and the fertility of these animals usually is not affected.

Post-breeding Discharges

Natural Service: The presence of a purulent vulvar discharge at 15 to 20 days after breeding (or estrus) typically is indicative of a uterine infection (metritis or endometritis). Affected animals invariably return to estrus. The causative agent likely enters the uterus during estrus. Sows bred late during estrus (often the third mating) are more susceptible to discharge problems. A specific pathogen responsible for all discharges has not been identified. Evaluation of the reproductive tracts at slaughter yields limited information because the animals have either resolved the infection or overgrowth of opportunistic bacteria has occurred.

Artificial Insemination: As mentioned previously, it was presumed that most, if not all, problems associated with vulvar discharges would be eliminated by the use of AI. This assumption was based on the concept that hygiene procedures would be dramatically improved with AI, compared to natural mating. Unfortunately, vulvar discharges continue to plague many sow farms.

The failure of AI to eradicate vulvar discharges was linked to mistakes in AI procedures, such as suboptimal estrus detection, poor hygiene of AI materials, insemination with contaminated instruments, and inseminations at an inappropriate time. Perhaps the most significant factor is related to estrus detection and the timing of matings. The results of several European studies revealed that insemination within 12 hours after the end of standing heat has a greater likelihood of inducing uterine infections than insemination prior to ovulation.

This relation between timing of matings and the occurrence of uterine infections is based on physiologic interactions between hormone concentrations and uterine defense mechanisms. Prior to ovulation, i.e. the initial two-thirds of standing estrus, the uterus is under the influence of estrogen. The high estrogen levels enhance uterine defense mechanisms, and thus, bacterial infections are almost impossible to induce at this time. Conversely, blood progesterone concentrations rapidly rise at the end of standing estrus and after ovulation. When progesterone levels rise above a certain threshold, uterine defense capacity is quickly lowered, which increases the susceptibility to uterine infections.

In practical terms, this detailed description simply implies that poor estrus detection and matings after ovulation (natural or AI) predispose sows to problems with uterine infections and vulvar discharges. In herds with vulvar discharges, we may need to re-examine our multiple mating schemes and the timing of mating relative to the onset of estrus. It is relatively easy to achieve three inseminations with AI. Without the use of stringent boar exposure and estrus detection, the goal of three matings per estrus may be creating problems rather than increasing sow performance.

Take-Home Message:

• AI has not eliminated problems with vulvar discharges.
• Estrus detection may be the key to solving problems with vulvar discharges.