bActivate Demonstrates Remarkable Improvement in Fertility Rates for Thoroughbred Mares

A collaborative study conducted with Kildangan Stud, one of the most prestigious thoroughbred breeding operations in Ireland and part of the Godolphin organisation, has produced some of the most compelling clinical evidence to date for the effectiveness of bActivate in problem mares.

The Study: 19 Barren Thoroughbred Mares

The study evaluated bActivate in a group of 19 barren Thoroughbred mares that had failed to conceive through conventional breeding and treatment approaches. These were not mares that had simply missed a cycle, they were established problem mares with histories of infertility that had resisted standard diagnostic and treatment protocols.

After completing the bActivate activation protocol, the results were as follows:

• 89% of the bred mares became pregnant (16 of 18; one of the 19 mares was not covered), at an average of 1.1 covers per mare
• Published as a congress abstract: Petersen, Rosenbrock, Osborne and Bojesen, J Equine Vet Sci 2018;66:117
• The protocol was completed within a single oestrus cycle prior to breeding

For context: a typical pregnancy rate in problem mares (mares that have failed to conceive through standard approaches) is 15 to 50%, against 80 to 85% in the general broodmare population (Bosh et al., 2009). An 89% outcome in a population of established barren mares is a clinically significant result.

Why This Result Matters for Thoroughbred Breeding

Thoroughbred breeding operates under unique pressures that make fertility failure particularly costly. The Northern Hemisphere covering season is fixed (February to July), mares must conceive early in the season to produce foals with maximum age advantage, and covering fees for top stallions can reach five- and six-figure sums. A barren season is not just a lost foal, it is a lost covering fee, a lost year of genetic progress, and in some cases a lost commercial opportunity.

At the elite level, stud farms like Kildangan work with mares whose genetic value demands the highest possible diagnostic precision. A culture-negative swab that is actually concealing a dormant Streptococcus zooepidemicus infection is not just an inconvenience, it is a failure of the diagnostic process with measurable commercial consequences.

The bActivate protocol addresses this directly by exposing the hidden infection before treatment, ensuring that antibiotic therapy is targeted at what is actually present rather than what a standard swab happens to detect on a given day.

The Science Behind the Result

The mechanism is well-established in peer-reviewed literature. Streptococcus equi subsp. zooepidemicus can enter a dormant persister state within the uterine endometrium. In this state, the bacteria:

• Are not detected by standard endometrial swab culture
• Do not respond to antibiotic treatment
• Persist through multiple breeding seasons
• Reactivate during oestrus, triggering inflammation that prevents embryo implantation

bActivate is a bacterial growth medium that, when instilled into the uterus during early oestrus, stimulates the bacteria out of dormancy within 48 hours. A post-activation culture taken at this point accurately reflects the infection, and targeted antibiotic treatment can then be applied.

The foundational research was published by Dr. Morten Rønn Petersen and Prof. Anders Miki Bojesen in Veterinary Microbiology (2015, DOI: 10.1016/j.vetmic.2015.06.006). The Kildangan/Godolphin study, along with the Hagyard Equine Medical Institute study (83% pregnancy rate in 64 problem mares), provides field-level validation of the laboratory findings.

Is bActivate Right for Your Mare?

If you manage thoroughbred mares or sport horse breeding programmes, and you have mares that have been barren despite normal cycles, clean swabs and previous antibiotic treatment, dormant uterine infection is the most likely undiagnosed cause. The bActivate protocol can be completed in a single cycle and is available through authorised veterinary distributors across Europe.

See all clinical studies including Hagyard and Copenhagen University data or find your nearest bActivate distributor.

Written by the Bojesen & Petersen Biotech ApS team. Medical oversight: Prof. Anders Miki Bojesen DVM PhD (University of Copenhagen) and Dr. Morten Rønn Petersen DVM PhD Dipl. ACT (Rigshospitalet).