Three clinical evaluations document what bActivate reveals, and what happens when the attending veterinarian treats the revealed infection. At Hagyard Equine Medical Institute (Lexington, KY), Dr. Kristina Lu's team activated and treated 64 problem Thoroughbred mares (barren for 3 or more cycles): 83% became pregnant (53/64) and 70% achieved live foals (32/46 with known outcome) (Petersen & Bojesen, Clinical Theriogenology 2014). At Kildangan Stud in Ireland, operated by Godolphin, 89% of the bred mares were in foal (16 of 18; one of the 19 mares was not covered) (Petersen, Rosenbrock, Osborne & Bojesen, J Equine Vet Sci 2018). The peer-reviewed laboratory study (Petersen et al., Vet Microbiol 2015) confirmed bActivate activated dormant bacteria in 64% of treated mares versus 8% in PBS controls (n=37). The studies were carried out at independent clinics and studs. The founders of bActivate are co-authors on the reporting of the results, and no placebo group was included in the two field studies.
The mares in these studies are the hardest group in broodmare practice. In the Kildangan cohort the average mare was 12.7 years old and had been barren for an average of 6.3 cycles before activation. Published research on a large commercial Irish Thoroughbred stud (2,385 mares, 3,743 oestrous cycles) identifies exactly this profile, high mare age and barren, slipped or rested status, as the significant risk factors for lower pregnancy rates and higher pregnancy loss (Lane et al., Reproduction in Domestic Animals 2016).
In other words: the mares bActivate is used on are the ones the published literature expects to do worst. After activation revealed the hidden infection and the stud veterinarian treated it, 89% of the bred Kildangan mares were in foal, at an average of only 1.1 covers per mare.
How to read this: these are separate datasets, not a controlled comparison, and the field studies included no placebo group. Lane et al. is cited for the difficulty of the mare group, not for bActivate, and shares an author with the Kildangan study team. Every figure on this page is attributed to the source that reports it.
The studies of bActivate itself were carried out by its developers and their clinical partners. The finding behind it, that dormant Streptococcus zooepidemicus in the uterine lining escapes routine culture, has since been taken up by research groups with no connection to the product. The 2015 activation study has been cited more than 60 times.
How to read this: these papers cite or describe the activation finding. None of them is an independent trial of bActivate, and none reports its own pregnancy or foaling outcomes with the product.
bActivate is independently referenced by the world's most respected equine veterinary publications and research institutions.
When treatment fails, consider resistant or dormant bacteria deep in the endometrium. bActivate "activates dormant Streptococcus zooepidemicus", so the uterus can be cultured and the mare treated on the result.
"...a (growth medium) product called bActivate, which activates dormant Streptococcus that can live within the endometrium, stimulating them to become metabolically active so we can treat them."
"The activation of dormant bacteria, using bacterial growth mediums like bActivate, may improve significantly the sensitivity of traditional diagnostics."
"Infusion of Bactivate when the mare is in estrus activates the dormant B.strep, increasing replication and growth, providing identification at 24 hours."
Study of 64 broodmares: 83% became pregnant (53 of 64) and 70% of mares with a known outcome foaled (32 of 46). No placebo group.
"Knap 10% af hopperne bliver aldrig drægtige trods dyrlægehjælp. Bactivate vækker sovende bakterier, så de kan diagnosticeres og behandles effektivt med antibiotika."
"bActivate, a growth medium specifically formulated to reactivate dormant Strep uterine infections, demonstrated effectiveness: bActivate-treated mares showed 64% bacterial activation versus only 8% in PBS controls."
A veterinary thesis project by Emilie Kähler Hjenner and Kathrine Kjeldsen Ravn at the University of Copenhagen, supervised by Prof. Anders Miki Bojesen, with Prof. Henrik Elvang Jensen (pathology) and Mette Christoffersen (equine reproduction) as co-supervisors. Submitted December 2025.
Standard culture had cleared these mares. They had been barren for one to three years regardless. So the question was not how common the infection is, but a narrower one: if the organism is suspected despite a clean culture, can it be shown to be physically present in the tissue? Sixteen archived endometrial biopsies were re-examined by fluorescence in situ hybridization. Streptococcus spp. were found in all 16.
FISH binds bacterial ribosomal RNA directly in fixed tissue, so it shows the organism whether or not it will grow on a plate, and it shows where in the endometrium it is sitting.
What they found
What it confirms
The suspicion was correct. The organism is present in tissue that cultures clean, and it sits below the depth a guarded swab reaches. That is why the swab fails. It is a question of geometry, not of test sensitivity.
It also confirms the sequence. FISH can see the bacteria but cannot treat them: dormant organisms stay antibiotic-tolerant until something wakes them. The two mares that could not be activated make the point. The infection was visible under FISH, it was never made treatable, and they stayed barren.
What it does not show
The authors set out to test whether the bacteria sit in areas of chronic degenerative change. They found this in only 2 of 13, and state plainly that they cannot say whether chronic infection drives endometrosis. Endometrosis behaved as a separate and irreversible problem: the higher the Kenney score, the poorer the outcome even once the infection was cleared.
Disclosure: a student thesis project, not peer-reviewed (published on Zenodo, DOI 10.5281/zenodo.23984203), supervised by one of the developers of bActivate. All 16 biopsies came from mares already selected as subfertile, and no healthy control mares were examined, so the work describes what is present in problem mares rather than how common it is generally. The authors note that routine diagnostic use of FISH would first require better knowledge of the normal uterine microbiome, to avoid overdiagnosis.
A clinical study at Hagyard Equine Medical Institute (Lexington, KY) led by Dr. Kristina Lu, reported by Petersen & Bojesen at the Society for Theriogenology Annual Conference 2014 (Clinical Theriogenology 6(3):313-314). A total of 64 Thoroughbred problem mares (barren ≥3 consecutive cycles) were included and subsequently bred.
Disclosure: As no placebo group was included in this clinical study, it is not possible to determine whether fertility was significantly increased following activation and treatment solely due to bActivate. The authors disclose this limitation in the proceedings.
This field study investigates the impact of latent infections caused by Streptococcus equi subsp. zooepidemicus on fertility in mares. Dormant bacteria are shown to persist intracellularly within the uterus, evading detection by traditional methods. These infections disrupt the establishment and maintenance of pregnancy, which is why an activation step is needed before standard culture can find them. bActivate reveals the dormant infection so the stud veterinarian can treat it with targeted antibiotics.
Conclusion
Latent infections significantly reduce fertility in mares, with dormant bacteria negatively affecting pregnancy outcomes. Activation dramatically improves diagnostic accuracy, and the veterinarian can then treat the infection the culture reveals. Published as a congress abstract: Petersen MR, Rosenbrock A, Osborne M, Bojesen AM, J Equine Vet Sci 2018;66:117. Also written up for breeders by the founders at SelectBreeders Services (2019).
This study explores how Streptococcus equi subsp. zooepidemicus invades and survives within epithelial cells, contributing to latent endometritis in mares. The research, led by Associate Professor Bolette Skive and Professor Manfred Rohde, reveals three distinct bacterial invasion mechanisms.
This study examines antimicrobial tolerance in beta-hemolytic streptococci (BHS) from problem mares, highlighting persister cells that tolerate penicillin at concentrations far above the normal MIC. After activation with bActivate the dormant streptococci grew in culture and could be identified, so the veterinarian could treat them.
This document provides scientific and practical evidence supporting the use of bActivate for revealing latent endometritis so it can be diagnosed and treated by the veterinarian. The study highlights the reactivation of dormant Streptococcus equi subsp. zooepidemicus infections.
FAQ
Common questions about problem mares, biofilm infections and bActivate activation.
In the largest clinical evaluation, at Hagyard Equine Medical Institute in Lexington, Kentucky, Dr. Kristina Lu's team activated and treated 64 problem Thoroughbred mares (barren for 3 or more consecutive seasons). 83% became pregnant (53 of 64 mares). A separate field study at Kildangan Stud, operated by Godolphin, reported an 89% pregnancy rate among bred problem mares (16 of 18). The studies were carried out at independent clinics and studs; the founders of bActivate co-authored the reporting of the results.
Standard uterine swab culture relies on active bacterial growth. In problem mares and non-pregnant mares, Streptococcus equi subspecies zooepidemicus often enters a dormant, biofilm-protected state deep inside the uterine endometrium. Dormant bacteria have a very low metabolic rate and do not grow on standard culture media, producing a false-negative result even when the infection is present and actively preventing conception. bActivate reactivates these dormant bacteria so they become detectable by standard culture within 48 hours.
The Hagyard clinical study included 64 barren Thoroughbred mares, all of whom had failed to conceive for 3 or more consecutive breeding seasons. The Kildangan/Godolphin study included 19 problem mares. A peer-reviewed laboratory study (Petersen et al., Veterinary Microbiology, 2015) included 37 mares and confirmed bActivate activated dormant bacteria in 64% of treated mares versus 8% in untreated controls.
Of the 64 problem mares treated at Hagyard, 53 (83%) became pregnant. Of the 46 mares with confirmed foaling outcomes, 32 (70%) delivered live foals. These were mares with a history of 3 or more failed breeding seasons before receiving bActivate.
Yes. The core laboratory science is published in Veterinary Microbiology (Petersen et al., 2015, DOI 10.1016/j.vetmic.2015.06.006), a placebo-controlled study confirming bActivate reactivates dormant Streptococcus zooepidemicus in mares. The Hagyard clinical data was presented at the Society for Theriogenology Annual Conference (Petersen and Bojesen, Clinical Theriogenology, 2014), and the Kildangan field study was published as a congress abstract in the Journal of Equine Veterinary Science (2018, DOI 10.1016/j.jevs.2018.05.162). The founders of bActivate are authors on these publications.
The Hagyard study was led by Dr. Kristina Lu at one of the world's largest equine hospitals, in Lexington, Kentucky. The Kildangan/Godolphin field study was run with Meta Osborne MVB at one of the world's premier Thoroughbred breeding operations, in Ireland. The clinics and studs are independent of the manufacturer; the founders of bActivate introduced the activation protocol and co-authored the reporting, which was presented at scientific conferences and published as a congress abstract in the Journal of Equine Veterinary Science (2018).
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