Equine Reproductive Medicine, Glossary

Also known as: dormant bacteria, persister bacteria

A dormant persister cell is a bacterial cell that has entered a metabolically inactive state as a survival strategy. In this state, the bacterium does not multiply, does not respond to antibiotics (which target active growth), and is not detectable by standard culture tests. In the mare uterus, Streptococcus equi subsp. zooepidemicus can persist in this state for months or years, causing chronic infertility despite negative swab results and antibiotic courses.

→ How bActivate reactivates persister cells

Also known as: Strep zoo, S. zooepidemicus

Streptococcus equi subsp. zooepidemicus (Strep zoo) is a beta-hemolytic gram-positive bacterium and the most common cause of uterine infection in broodmares, accounting for approximately 80% of bacterial isolates in positive endometrial cultures. In mares with chronic infertility, Strep zoo can enter a dormant persister state within the deeper endometrial glands and stratum compactum, a location unreachable by routine swab culture.

→ German study: bacterial spectrum in mare uterine health

A biofilm is a structured community of bacteria enclosed in a self-produced matrix of proteins and polysaccharides. In the equine uterus, Streptococcus zooepidemicus biofilms adhere to the endometrial surface and render the bacteria resistant to both host immune defenses and antibiotic treatment. Biofilm-associated infections are a major cause of chronic, recurrent endometritis in problem mares that do not respond to repeated antibiotic therapy.

→ How bActivate tackles biofilm and dormant bacteria

Also known as: latent uterine infection, dormant endometritis, hidden uterine infection

Subclinical endometritis is uterine inflammation in the absence of clinical signs such as discharge, fever, or irregular estrus cycles. The mare appears reproductively normal, but microscopic inflammation or low-grade infection prevents successful embryo implantation. Because the condition produces no obvious symptoms and standard swab cultures have a detection sensitivity of approximately 34%, subclinical endometritis is one of the most common causes of unexplained infertility in problem mares.

→ Guide to endometritis in mares

Also known as: barren mare, empty mare, repeat breeder

A problem mare is defined as a mare that fails to conceive despite breeding to a stallion of proven fertility over three or more consecutive estrus cycles. The term encompasses a range of underlying causes, but in the published activation series, 47 to 87% of problem mares carried a dormant Streptococcus zooepidemicus infection that the standard swab had missed.

→ Addressing the challenges of problem mares

Also known as: older maiden mare

A maiden mare is a mare that has never been bred, or, in sales catalogs, never been covered. The older maiden mare, bred for the first time from about 12 years, is the mare breeders write about most: often bred with frozen semen, often building fluid after covering, and often sent home with a clean culture and cytology and no pregnancy. Maiden status itself does not protect against a dormant infection; age does the opposite, because the lining clears bacteria less well with age. An older maiden mare with a clean swab and no pregnancy deserves the same work-up as a barren mare.

→ Is my mare a candidate?

A high-risk mare is one with one or more of the following characteristics: 12 years of age or older; three or more previous foals (multiparous); a history of pregnancy loss or abortion; or a documented previous episode of endometritis. In the published series this group had the highest activation-positive rates (up to 84% at Kildangan, where the average mare was 12.7 years old and 6.3 cycles barren). High-risk mares are the primary indication for bActivate screening.

→ When to use bActivate, risk indicators

Estrus, or heat, is the phase of the mare's cycle in which she accepts the stallion and a follicle matures towards ovulation; in the breeding season it typically lasts about five to seven days. Early estrus is the first days of that phase, when the cervix is relaxed and the uterus is best able to clear fluid. bActivate is instilled in early estrus so that the 48-hour culture and any treatment fall before ovulation; the mare is bred in the following cycle.

→ How bActivate is used, step by step

The uterus's own means of clearing bacteria and inflammatory fluid after breeding: uterine contractions that expel fluid through a relaxed cervix, lymphatic drainage, and the local immune response of the endometrium. In mares with weakened defense mechanisms, typically older mares, mares with several previous foals, or mares with poor perineal conformation or a pendulous uterus, fluid and bacteria remain in the uterus after breeding and a persistent endometritis can follow. These are the mares listed as candidates on the when to use page.

→ When to use bActivate

Antibiotic treatment chosen on the basis of a culture and an antibiogram: the laboratory grows the bacteria from the uterine sample, identifies them and tests which antibiotics they are sensitive to, and the veterinarian prescribes accordingly. It is the opposite of empirical treatment, where an antibiotic is given without a culture result. bActivate makes targeted treatment possible in the problem mare by turning a dormant, culture-negative infection into a culture-positive one within 48 hours; the treatment itself is the veterinarian's, not the product's.

→ Full bActivate protocol (5 steps)

Reactivation, in the context of equine endometritis, refers to the process of stimulating dormant persister-state bacteria in the uterus to resume active metabolic growth. bActivate achieves reactivation by instilling a bacterial growth medium directly into the uterus during early estrus. Within 48 hours, previously undetectable Streptococcus zooepidemicus becomes culture-positive, enabling targeted antibiotic treatment. The reactivation principle was first described by Petersen and Bojesen in Veterinary Microbiology (2015).

→ Full bActivate protocol (5 steps)