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General biosecurity considerations for equine breeding facilities, concentrating on sexually transmitted diseases

Introduction: The goal of a biosecurity program at a breeding facility is to reduce the risk of introduction of an infectious disease organism onto the site and/or to reduce the risk of spread of an infectious disease organism at a facility. 

Natural service (live cover) and AI are associated with inherent infectious disease risks.  Advanced reproductive procedures (e.g., embryo transfer, oocyte transfer and intracytoplasmic sperm injection followed by embryo culture and transfer) may also be mechanisms for transmission of infectious disease agents.  For example, viruses (particularly Equine Arteritis Virus) can be very difficult, if not impossible, to remove from equine embryos despite being subjected to multiple washes; accordingly, this may result in infection of recipient mares upon transfer. 

Although horses used for breeding are the focus of these guidelines, non-breeding equids must also be considered when evaluating biosecurity.  For example, when a mare is exposed to infection at a breeding facility and returns to her farm of residence to her foal, the foal is at risk of acquiring infection from its dam.  Therefore, a biosecurity plan for an equine breeding farm must also include provisions for management of newborn foals, weanlings and yearlings. 

Live cover or natural service refers to mating in which a stallion mounts a mare, intromits the penis into the vagina and ejaculates.  Live cover breeding has generally been thought to provide greater risk of venereal disease transmission than AI.  However, AI with contaminated fresh, cool-transported or frozen semen can also be responsible for transmission of venereal pathogens. 

Infectious diseases that are important in the equine breeding industry are not limited strictly to agents transmitted during coitus or insemination.  Stallions, mares and foals are at risk of disease from a wide variety of infectious organisms (viruses, bacteria, parasites).  The mode(s) of transmission and propensity to spread to other horses on a farm vary with each organism and the susceptibility of the at-risk population. 

Internal parasites continue to be a problem at horse facilities, including breeding farms.  Resistance to certain anthelmintics is a problem of increasing importance in many geographical areas.  Appropriate identification of parasitized horses and development of a strategic deworming program should be a high priority and an integral part of an overall herd health preventive medicine program.   

General guideline considerations: Biosecurity guidelines for equine breeding programs should be tailored for each individual operation.  Specific biosecurity measures employed should depend on potential risk, geographic location, animal density, horse traffic, ages of resident horses, breeding management procedures (e.g. live cover versus AI) and other factors, such as importation of embryos or preserved semen.  Biosecurity protocols should be understood by all facility personnel and followed on routinely.  State and federal animal health authorities must be notified should a reportable venereal disease be suspected. 

Managers of breeding operations, and their attending veterinarians, must understand and comply with all federal and state/provincial regulations regarding health status testing.  Examples include testing for Equine Infectious Anemia (EIA) and procurement of a health certificate from an accredited and licensed veterinarian prior to transport, as well as prebreeding testing and vaccination of serologically-negative stallions against Equine Viral Arteritis (EVA), or testing for Taylorella equigenitalis (CEMO) where required (e.g., following initial importation, or upon return from breeding in a different hemisphere).  The window of time given for collecting samples for testing and reporting can be narrow.  To verify testing requirements in your area, please check with your state/provincial animal health office (see State Veterinary Offices in the AAEP Resource Guide and Membership Directory) and USDA-APHIS animal health regulations.  

While this communication specifically addresses venereal diseases, the potential modes of transmission of any disease agent on a breeding farm include: 

  1. Direct horse-to-horse, especially nose-to-nose, contact.
  2. Respiratory transmission by aerosol or droplet of an agent from one horse to another.
  3. Oral (ingestion), especially contaminated hay, grain or water or contact with contaminated surfaces (stall floor mats, walls, drains, stocks).
  4. Venereal transmission by live cover or AI.
  5. Fomite exposure, including contaminated semen collection/processing/insemination equipment, phantom, breeding rolls,  stocks, trailers, stalls, farm equipment, vehicles, grooming equipment, halters, lead ropes, twitch, water buckets, water hoses, shared needles, clothing, footwear and hands of personnel, etc.
  6. Transmission of infectious agents through advanced reproductive techniques, such as embryo transfer, oocyte aspiration or transfer, or intracytoplasmic sperm injection (ICSI).
  7. Vector-borne transmission (insects, ticks).