Risk factors associated with uterine fluid after breeding caused by Streptococcus zooepidemicus.

This study investigates the correlation between varying risk factors for broodmares — such as age, parity, and vulvar conformation — and the contraction of infectious endometritis, a significant contributor to infertility commonly caused by the bacterium Streptococcus equi subsp. zooepidemicus. The findings suggest that older, multi-parous mares with poor vulvar conformation showing clonal S. zooepidemicus infections have lower pregnancy rates compared to those with two strains isolated.

Research Objectives

• The study’s main objective was to understand the relationship between different risk factors in mares, infectious endometritis (an infection of the uterus causing infertility), and pregnancy rates in broodmares (mares used for breeding).
• The researchers further aimed to investigate whether distinct strains of the Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) bacterium, isolated from mares with endometritis, were associated with specific mare risk factors and the outcome of insemination.

Key Findings

• The researchers found that 20% of the observed mares (a total of 152) had intrauterine fluid accumulation after natural mating, indicating the presence of endometritis.
• S. zooepidemicus was isolated in 81% of mares with detected intrauterine fluid, affirming the bacteria’s prominence in causing endometritis.
• Mares not involved in the breeding process (“resting mares”) showed a higher instance of intrauterine fluid compared to the ones who recently gave birth (“foaling mares”), hinting at a higher risk of infection for resting mares.
• Overall, pregnancy rate dropped significantly with advanced age and greater parity (a higher number of births). The lowest pregnancy rate was recorded in resting mares compared to the counterparts like foaling, barren, and never-bred (“maiden”) mares.
• On further studying the genetics of the isolated bacterial strains using pulsed-field gel electrophoresis, the researchers identified distinct patterns within each mare, even isolating two genetically unique strains in five mares.
• A clonal (genetically identical) S. zooepidemicus infection was notably associated with older mares of high parity and poor vulvar conformation. These mares also showed a lower pregnancy rate.

Conclusions and Implications

• The results of the study suggests, that clonal S. zooepidemicus endometritis, which renders a lower pregnancy rate, occurs more often among older, high-parity mares with poor vulvar conformation.
• These findings can be used by the equine breeding industry to modify breeding plans for mares based on risk factors to reduce the occurrence of endometritis, thereby improving fertility rates and economic efficiency.
• Additionally, a better understanding of the bacterial strains causing endometritis can guide the development or enhancement of current treatment options for the condition.