Top Equine Repro Studies of 2019

Each year at the American Association of Equine Practitioners convention, a panel of researchers present what they believe to be the top studies with clinical implications from the past year. At the 2019 meeting, held Dec. 7-11 in Denver, Colorado, Regina Turner, VMD, PhD, Dipl. ACT, section chief of reproduction and behavior at the University of Pennsylvania’s New Bolton Center, shared her favorite breeding-related papers on topics ranging from foaling prediction to estrus suppression.

A Comparison of Foaling Prediction Technologies

“We all know mares have a very sneaky and bad habit of doing everything they can to foal without humans present,” said Turner as she introduced the first study. “As a result, we humans have attempted to develop foaling prediction technologies to outsmart these mares and catch them in the act of foaling.”

In this study, researchers from Canada and the UK compared foaling prediction technologies in periparturient Standardbred mares in an attempt to define which ones were the best at accurately predicting when a mare would deliver her foal. This is the first study comparing several technologies against one another, Turner said.

The team looked at six popular foaling technologies:

  1. Calcium titration methodology (e.g., Foal Watch) Using this method, the breeder or veterinarian dilutes mammary gland secretions in a series of steps, then assays calcium levels. At $2 per test, it’s very inexpensive. “This test proved to be the most sensitive of any of the tests examined, with an 87% true positive rate,” said Turner, “meaning if calcium levels rose above a certain level and the test predicted the mare would foal, there was an 87% chance she would foal that night.”
  2. Ca/Mg test (e.g., MQuant, which is based on a water hardness kit) “This test is a bit easier to use because it only requires one dilution instead of a series of dilutions and relies on a little less volume to perform,” said Turner. “However, this test was less sensitive, coming in at around 71%.” It costs only $1 per test.
  3. Digital pH meter (e.g., Hanna) This pH-based methodology uses a $360 meter to assay mammary secretion pH.
  4. pH strip (e.g., Hydrion) This easy and affordable ($.25/test) method involves placing a single drop of mammary secretion on a pH strip and looking for a color change that indicates pH is dropping.

Both these pH-based methodologies were very specific—the two most specific of the tests assayed, said Turner, meaning they had a high true negative rate. “So 72% and 82% of the time, when these assays predicted that the mare would not foal, she did not,” she said. “So if you combine the most sensitive technique—the calcium titration method—with one or the other of these pH technologies, you had a very good chance of predicting correctly one way or the other whether a mare would foal over the next three days.”

  1. Refractometer (e.g., Brix) Turner said this method performed very poorly and shouldn’t be used to predict foaling in mares. It costs about $100 per meter.
  2. External birth monitoring system (e.g., FoAlert) This system gets sutured onto the mare’s vulva, and when the foal passes through the birth canal and the vulvar lips separate, a magnet gets pulled out of a base station, triggering an alarm. It costs just over $1,000 a system and has a similar sensitivity as the calcium titration (84% true positive). “This makes us happy because it means when the system goes off and we run out to catch the mare, she is often actually foaling,” said Turner. “It had a pretty good false negative rate (16%) similar to both the pH methods. This is really important because this is the error we want to avoid most critically. This is when the alarm does not go off, but the mare actually foals.” The system also had a good false positive rate: Only 11% of the time did the alarm go off when the mare was not foaling.

“In summary, if you see any of these foal monitoring systems that say they eliminate the need for nightly foal sitting, that is not true,” said Turner. “None of these assays were 100% accurate at predicting foaling, and you’re going to have to face the fact that you’re going to lose some sleep if you have a periparturient mare. You need to hire skilled staff 24/7 to have your eye on the prize and actually catch those mares foaling.”

If you are going to rely on foaling prediction technologies, the study authors recommended combining calcium titration with one of the pH technologies. The birth monitoring system is probably the single best test if you’re only going to pick one, but it’s also the most expensive. Turner advised considering practicality as well as cost when making a decision.

“If you have one of those mares that simply can’t stand it when you touch her udder and tries to kill you, then all of these mammary secretion technologies are probably off the table, she said. “Similarly, for the owner with one or two backyard mares, the birth monitoring system is probably not cost-effective.”

Diel de Amorim M, et al. Comparison of Foaling Prediction Technologies in Periparturient Standardbred Mares. Journal of Equine Veterinary Science, Volume 77, June 2019, 86-92

Breeding Older Mares: Consider ICSI

In a new study, Dutch researchers set out to investigate the effects of maternal age and breeding technique on the likelihood of producing a viable pregnancy from older mares.

“We’ve known for many years that advancing age is one of the primary components to reduced fertility in the horse, and we thought this was due to a decline in oocyte quality primarily rather than a decline in uterine quality,” said Turner.

To determine whether this is true, the team compared older mares’ reproductive efficiency using four breeding techniques: natural mating, artificial insemination (AI), embryo transfer (ET), and intracytoplasmic sperm injection (ICSI). They noted a significant decrease in reproductive efficiency as mares age using the first three methodologies.

“But if you look at ICSI, you see no statistically significant change as the mares age,” said Turner. “So it’s telling us that we are not seeing a decline in oocyte quality. ICSI relies essentially only on the oocyte of the donor mare, and we don’t see any decline in efficiency from when the mare is in the youngest group to when she’s in the oldest group.”

Mares in the ICSI group also tended to produce multiple embryos per session.

In summary, increasing maternal age was associated with reduced pregnancy rates in all breeding techniques except ICSI, with the strongest negative effect on reproductive efficiency in mares bred to carry (natural mating, AI).

“So maybe it’s time to start rethinking our reasoning as to why old mares lose fertility as they age,” said Turner. “It appears to not be primarily due to aging of the oocyte. Oocytes from ICSI mares had just as good blastocyst development, just as good maturation as they did when these mares were younger. The difference was older mares tended to produce fewer oocytes, but the oocytes they did produce seemed to be of the same quality as when they were younger.”

She hypothesized that there might instead be a uterine effect.

While this study shows that ICSI might be the breeding technique of choice for older mares, Turner cautioned that it’s much more expensive than the other techniques and does come with risks because it’s an invasive procedure.

Cuervo-Arango J, et al. A retrospective comparison of the efficiency of different assisted reproductive techniques in the horse, emphasizing the impact of maternal age. Theriogenology. 2019 Jul 1;132:36-44.

Researchers Identify Trotting vs. Pacing Gene in Standardbreds

An international group of researchers recently sought to identify genetic variants that underly pacing in Standardbreds. Scientists have known for years that a mutation on a gene called DMRT3, first discovered in Icelandic horses, is nearly fixed in all gaited breeds and absent in nongaited breeds. DMRT3 is expressed in the spinal cord, suggesting it plays a role in the development of normal locomotive function. This mutation is present in essentially all Standardbreds, whether they’re trotters or pacers, so there must be more things involved in determining the variability of gaitedness seen in Standardbreds.

This research group hypothesized that  additional modifying genes or alleles must exist that determine whether a Standardbred will trot or pace. They did a genome-wide association study to compare genetic variants between trotters and pacers at the whole genome level. They studied the genomes of more than 500 horses, looked at tens of thousands of single nucleotide polymorphisms (SNPs), and identified seven that could be used in an algorithm to correctly predict whether a horse would trot or pace more than 99% of the time.

“This paper is the first to start to look at genetic variation on a large scale,” said Turner. “Where we want to go is being able to predict genetically polymorphic traits, polygenic traits—things like whether an animal will run fast or jump high or look pretty. Those are much more difficult to assay for because they likely involve hundreds, maybe thousands, of genes on top of how the horses are raised and trained. This study is one of the first to look at numerous markers across the whole genome to predict traits in horses.”

She said she believes this type of testing is the future of breeding and veterinary medicine. “It could influence breeding and training decisions relative to gait,” she said. “And it could be important to research on coordinated gait development. It’s likely to be applicable to other gaited breeds, as well.

“We’re still very much in the infancy of genetic testing, but this is coming, and you should be aware of it,” Turner concluded.

McCoy AM, et al. Identification and validation of genetic variants predictive of gait in standardbred horses. PLoS Genet. 2019 May 28;15(5):e1008146.

New IUD Option for Mares Is Safe and Effective

“Whether it’s true or not, there’s a perception that mares in estrus can behave in ways that can interfere with handling and competition,” said Turner.

So in this study, a team of researchers set out to develop a safe and reliable method for suppressing estrus (and, thus, minimize adverse behaviors) in mares—an intrauterine device to replace the now unfavorable intrauterine marble.

Over five years, the team worked with a large number of mares and engineers to develop a device composed of three small, egg-shaped magnets that assemble into a stable triangular configuration upon being inserted into a mare’s uterus. Called Upods, these devices are visible on ultrasound and identifiable with a magnet detector run over the mare’s abdomen. The veterinarian simply inserts a magnetic retriever into the uterus to fish them out.

To find out if the Upods work, the researchers compared three study groups.

  • Controls without devices, which experienced an average diestrus (the period between estrous cycles) of about 17 days.
  • Mares administered Upods the day after ovulation, which experienced an average diestrus of more than two months.
  • Mares administered Upods at any time during the estrous cycle, which experienced a similarly prolonged diestrus as those inserted the day after ovulation.

The mares had 100% retention rate and no negative effects on biopsy. Eight mares bred after having the Upods removed had 100% pregnancy rates that next season, suggesting the devices don’t adversely affect fertility.

“They also said Upod mares exhibited subdued estrus behaviors and improved rideability and that there was a general demeanor shift, even when mares were in estrus,” said Turner. “This was subjective though.”

So in summary, these devices:

  • Have a high retention rate;
  • Are almost certainly safer than marbles, which can shatter in the uterus or be lost;
  • Can be detected readily by the owner or veterinarian; and
  • Are easy to insert and retrieve.

Further, the researchers have postulated that they might be useful as a contraceptive for feral horses. They hope Upods will be available on a limited scale in early 2020, but production has been slow.

Gradil CM, et al. Self-Assembling Intrauterine Device (Upod) Modulation of the Reproductive Cycle in Mares. Journal of Equine Veterinary Science Volume 83, December 2019, 102690