Written by: Heather Clemenceau
We’ve known for many years that farm animals have been exploited to produce more meat, milk, wool etc. Embryo transfer in horses is another technology that is unrivalled for its inefficiency and costliness. There’s also some evidence that embryo transfer (ET) is exploitative because it can be painful, requiring analgesics. We recently read about the cast-off recipient mares (the “gestational” carriers that give birth to foals of a different mare/stallion) from the Arnold Reproduction Center who were consigned to the Kaufman kill pen/kill buyer Mike McBarron for eventual slaughter. Once exposed on social media platforms, veterinarian Leea Arnold responded:
“I recently sent some mares to the Cleburne Horse Sale. I certainly never intended for them to end up in the slaughter pen. Many of these mares came to me through the sale barn system, were sick, completely unbroken and certainly destined for slaughter at that time (15 or so years ago). As long as these mares are reproductively sound, they stay in my herd – many probably longer than they are useful. My staff and I have taken the time, money, and resources we have to help these mares become useful and give them a viable purpose.
“I will use another avenue to re-home these mares in the future. If you are a non-profit organization and have your 501(c)3 at hand, I would be more than happy to donate any older or reproductively unsound recipients to your facilities as they become available.”
Dr. Arnold did not otherwise offer to help the animals that were scheduled to be sent for slaughter.
In addition to horses, mules are also being used in at least one euphemistically named “mule mom” program using embryo transfers from gypsy vanner mares. The Gypsy Gold breeding program in Ocala Florida charges up to $14,000 for a purebred gypsy vanner foal carried by a mule, who is often shipped to and from the Gypsy Gold Horse Farm and the contractor of their service. They also helpfully offer a service for purchasers of the gypsy foal who are not satisfied with the quality of their new purchase – they will connect you with an “appropriate buyer” – quite possibly the same buyer who will purchase the mule moms once their fertility wanes. At the moment, this farm offers 11 mares for breeding, so one can only imagine how many times they are being flushed out and the number of “mule moms” that are being used as gestational carriers.
Currently, most equine breed associations permit embryo transfer. Notable exceptions include the Jockey Club (thoroughbreds), the United States Trotting Association, and the American Miniature Horse Association. Brazil and Argentina are currently the leaders in equine ET, although it’s believed that about 10,000 embryos were collected and transferred in the USA in 2014. The practice seems to have become more widespread in 2015, with more countries reporting embryo transfer activities, including Canada, South Africa, France, Poland, Switzerland, the USA, and Mexico.
Why is Equine Embryo Transfer Also A Welfare Issue?
Because veterinarians can only flush fertilized eggs (embryos) from the uterus of a donor mares at specific times the cycles of one or more recipient mares must be synchronized with the donor mare. This is why reproductive vet clinics tend to have a wide selection of recipient mares from which to choose. The number of mares that some vet clinics keep on hand for this purpose varies from dozens of mares to hundreds. In many cases the donor mare is synchronized with two or more recipient mares in the event that multiple embryos are recovered from the donor mare. Obviously, these mares’ “jobs” come with no guarantee of a home placement after their careers are over and may easily fall into the wrong hands.
There are potential welfare issues for a donor mare, including those associated with the flushing procedure and with repeat injections to attempt to induce ovulation when used. Because more than two mares may be involved, the number of invasive rectal and ultrasound examinations is increased. Where recipient mare numbers are limited, greater pharmacological manipulation (often involving repeated injections) may also be used to achieve ovulatory synchronization between donor and recipient mares.
While there are apparently no studies on whether ET is painful in mares, it is known to be painful in other species, especially those in which embryo flushing is a surgical procedure. Perhaps because of this it is common practice to sedate mares both during flushing and ET.
Transvaginal ultrasound-guided follicular aspiration in women is known to be associated with pain, the severity of which is dependent upon needle design. In sheep and goats, repeated surgical egg retrieval has been associated with the development of adhesions. In a study of pony mares who were the subject of invasive follicular procedures, it was observed that heart rates and cortisol levels increased considerably as soon as a needle was introduced into the procedure.
Lastly, the development of the “super ovulation” protocol and the resulting production of more oocytes (cells that develop into an ovum/egg) will heighten the possibility of more foals using larger herds of recipient mares, greater numbers of horses born that aren’t needed, and more slaughter after the recip mares are no longer required.
Drugs/Hormones Commonly Used in Equine Reproduction Practices and Their Withdrawal Times
Sources for withdrawal times were the Meat Hygiene Manual of the CFIA or drug datasheets. It is important to note that withdrawal times are often extended when drug
Most donor mares are sport horses, Arabians or Quarter Horses. It’s an appealing option for those who can afford it, since it allows the option of the owner taking their mare out of competition for only about a week in order to produce a foal.
combinations are used. Drugs used off-label in unapproved species may have differing withdrawal times even though appropriate dosage is given and whether used in combination with other drugs. The dose itself along with the frequency of use (repeated oral administrations can greatly extend withdrawal times) are two of the most important factors. Compounded drugs (as opposed to generic or branded drugs sold OTC or through veterinarians) can vary widely in potency as well. The amount of body fat, the breed, gender and health of the horse are also factors that affect kinetic decay of drugs. Lastly, the amount of stress that the horse is subject to may also affect withdrawal times. And even though a pharmacological effect on the animal may be over, the drug and its metabolites may still be detectable, and those metabolites may also be prohibited. The CFIA manual doesn’t tell anyone this, nor could they expect the lay horse person to understand any of the factors that also affect withdrawal times and drug tests,
Altrenogest/Progesterone/ Medroxyprogesterone (synthetic variant of hormone progesterone)
- Trade name: Regumate®, Depo-Provera® (medroxyprogesterone)
- Class of Drug: Hormone
- Use: Clinical uses include synchronizing the ovulations of a donor mare with a specific recipient mare. It may also be used to alter or manipulate the estrous cycle of a mare for a scheduled breeding due to stallion availability.
- CFIA Withdrawal/Prohibition: 42 days withdrawal
Flunixin meglumine
- Trade Name: Banamine®
- Class of Drug: non-narcotic, nonsteroidal, analgesic agent with anti-inflammatory and antipyretic activity
- Use: Reduces moderate inflammation by stopping the formation of prostaglandins, which are mediators of inflammation. They also reduce the formation of certain pain-causing products of inflammation. Embryo recipients may receive flunixin meglumine i.v. at the time of transfer.
- CFIA Withdrawal/Prohibition: IV – 10 days/IM 30 days
Vedaprofen
- Trade Name: Quadrisol, VETRANAL™
- Class of Drug: Analgesic, antipyretic and anti-inflammatory agent, Non-steroidal anti-inflammatory drug, NSAID
- Use: For the control of inflammation and relief of pain associated with musculo-skeletal disorders and soft tissue injuries in horses
- CFIA Withdrawal Prohibition: 21 days (oral and IV)
Human chorionic gonadotropin (hCG)
- Trade Name: Chorulon®
- Class of Drug: Gonadotropin releasing hormone or GnRH
- Use: Can also be administered to mares to accelerate ovulation selectively where needed to improve the degree of synchrony between the donor and recipient mares. Induces ovulation in mares. Induction of ovulation is advantageous if a mare is in a timed breeding, shipped semen, frozen semen or embryo transfer program.
- CFIA Withdrawal/Prohibition: 0 days
Deslorelin Acetate
- Trade Name: Ovuplant™ SucroMate™
- Class of Drug: Gonadotropin releasing hormone or GnRH
- Use: A potent, synthetic form of GnRH. The drug is administered as a subcutaneous implant.The most common use in a breeding program is the induction of a timed ovulation, such as when mares are being bred with cooled-transported semen or frozen semen
- CFIA Withdrawal/Prohibition: not on CFIA website but listed with a “WARNING: For use in horses (estrous mares) only. Do not use in horses intended for human consumption. For intramuscular (IM) use only. Do not administer intravascularly. Not for use in humans. Keep this and all drugs out of reach of children.”
Lidocaine Hydrochloride
- Trade Name: Lidoject, Lidocaine HCI 2% etc.
- Class of Drug: Local anesthetic and anti-arrhythmic agent.
- Use: Skin block for sutures and implants
- CFIA Withdrawal/Prohibition: 7 days
Prostaglandins
- Trade Name: Lutalyse®, Prostin®, Estrumate®
- Class of Drug: Fatty acid compounds with varying hormone-like effects
- Use: Prostaglandins are commonly administered to mares in a timed breeding program or after having missed a breeding opportunity to bring mares back into estrus. Prostaglandins are one of the most widely used hormones in equine reproduction.
- CFIA Withdrawal/Prohibition: not on website, but listed elsewhere. “must not be slaughtered for use in food for at least 2 days after the latest treatment with this drug.”
Domperidone
- Trade Name: Equidone®
- Class of Drug: Dopamine antagonist. Neurotransmitter
- Use: Modulates or suppresses production of the hormone prolactin from the pituitary. In breeding programs it stimulates lactation or the induction of lactation in nurse mares or the induction of follicular development. Also used as a preventative for fescue toxicosis.
- CFIA Withdrawal/Prohibition: “no known manufacture for veterinary use in Canada”
Oxytocin
- Trade Name: OxoJect™, Oxytocin-S
- Class of Drug: Hormone
- Use: Administered to mares for evacuation of uterine fluid and treatment of retained placenta. It may also be used for induction of labor in late term mares and milk let-down.
- CFIA Withdrawal/Prohibition: not on website: 0 days
eFSH
- Trade Name: FOLLTROPIN®
- Class of Drug: Hormone
- Use: Facilitates “superovulation” – ovulating from more than one follicle at a time. Development of a s protocol to superovulate mares would allow a top mare to produce several foals in a year, or to have several embryos frozen for later use. The hormone is extracted from porcine pituitary glands.
- CFIA Withdrawal/Prohibition: not on website but listed elsewhere. “Treated animals must not be slaughtered for use in food for at least 10 days after latest treatment with this drug.”
The welfare of the animal is always compromised when greed is involved. The ability for breeders to implant multiple embryos with no limits caters to the wealthy individuals in the industry. 
While one might argue that ET is less risky than foaling for a mare, horses should not have litters, especially since there is some question whether it is humane to repeatedly subject both recipient and donor mares to invasive procedures, after which many horses are dumped. The worst but hardly the only offender of this practice, the AQHA, allows multiple-embryo-transfer rules that facilitate overpopulation by allowing mares to have more than one foal per year. Rules about using frozen semen or eggs from long-sterile or dead animals have allowed horses to breed from beyond the grave. Consider that First Prize Dash, a 1988 quarter horse mare – produced 44 offspring! Her sire, Dash for Cash, sired 1,233 foals!
It is also very doubtful that either Canadian or Mexican slaughterhouses have tested for some of these lesser used or less obvious drugs or hormones. Since some drugs/hormones are not even line items in the Meat Hygiene Manual, it would be easy for sellers of horses to plead ignorance of the requirement to disclose on an EID. Embryo transfer therefore facilitates an already unsavory horsemeat industry in novel, previously unanticipated ways.
