Subclinical infections caused by persistent bacteria are recognized as an increasing therapeutic challenge. The inefficiency of antimicrobial treatment is not due to inherited resistance but merely a matter of metabolic slowdown of an initial small number of bacterial cells leading to inefficacy of most antimicrobials.
In mares the leading cause of endometritis is Streptococcus equi subsp. zooepidemicus (Sez). While most uterine infections are readily cleared by antibiotics an estimated 5-10% of mares have a subclinical infection caused by persistent Sez. To investigate the impact of subclinical endometritis we tested a commercial product, bActivate, which appears able of re-activating the dormant Sez allowing subsequent antimicrobial treatment, to evaluate the effect on breeding efficacy.
A total of 64 gynecologically normal mares barren for > 3cycles despite intensive breeding management were included in the investigation. All mares were culture-negative for Sez on day 0 and changed to culture-positive for Sez (> 5 CFU ) within 24 hrs after instillation of 10 ml bActivate, a commercial growth medium. Infections were treated with systemic and intrauterine antimicrobials, ecbolics, uterine lavage, and bred in the following estrus cycle.
Pregnancy was established in 53 (83%) mares whereas 21 pregnancies was established in 2011 and 18 (86%) gave birth to a live foal the following year. Since all mares were instilled with the activation solution, the pregnancy rate of non-activated mares cannot be determined.
Considering previous estimations of the expected foaling rates (15 to 50% live foaling rate) for barren mares (> 3cycles) our results clearly indicate that activation and subsequent antimicrobial treatment of dormant S. zoo in problem mares can restore the expected pregnancy and live foal rates to levels reported for the general broodmare population (80 to 85% live foaling rate) (Bosh et al., Equine Vet. Journal, 2009).