Top Reproduction Studies of 2017

Each year, the annual American Association of Equine Practitioners convention kicks off with a rapid-fire run through some of the past year’s most important surgery, medicine, and reproduction studies. The 2017 edition, held at the Nov. 18-21 meeting in San Antonio, Texas, featured Regina Turner, VMD, PhD, Dipl. ACT, chief of the Section of Reproduction and Behavior at the University of Pennsylvania’s New Bolton Center, in Kennett Square, presenting reproduction research. Here were her top five selections:

1. Platelet-Rich Plasma (PRP) Can Help Treat Persistent Mating-Induced Endometritis

A group out of Brazil investigated the effects of administering intrauterine PRP on uterine inflammation (endometritis) and conception rates in mares with persistent-mating induced endometritis (PMIE).

“It’s normal after semen enters the mare’s uterus for the uterus to have an inflammatory response. This aids in normal uterine clearance,” said Turner. “That inflammatory response should resolve within 12 hours of breeding. If it persists we put these mares into a high-risk category and refer to them as PMIE mares. Mares with PMIE have lower chances of becoming pregnant following breeding.”

Knowing that PRP has anti-inflammatory effects, the Brazilian team hypothesized that administering PRP into the uterus might decrease inflammation and increase pregnancy rates in PMIE mares. They evaluated the uterine inflammatory response after artificial insemination (AI) in 13 mares with known histories of PMIE. Each mare was bred once over each of three estrous cycles. For the control cycle, researchers administered no treatment. In the second cycle, the researchers infused mares with PRP 24 hours prior to insemination, and in the third cycle, they infused mares with PRP four hours after insemination.

“There was a significant decrease in markers of inflammation in both treated cycles compared to the control cycles,” said Turner. “Similarly, on histology (microscopic evaluation of cells) and biopsy there was a significant decrease in evidence of endometritis in PRP-treated mares.”

To determine if this decrease translates to improved fertility, the team followed mares to 14 days post-ovulation to determine pregnancy rates on each cycle. They found that untreated control PMIE mares had a pregnancy rate of about 30% and treated mares (when both treatment groups were combined) had pregnancy rates over 60%.

“So they’ve shown an increase in pregnancy rate and an associated decrease in inflammation in mares susceptible to PMIE when treated with PRP compared to when these same mares are not treated,” said Turner.

Because the method of PRP production that this team used is very simple, she suggested veterinarians consider adding PRP intrauterine infusions to their list of potential treatments when dealing with PMIE mares. She cautioned, however, that since PRP decreases the uterine response to contamination, it might not be the best choice for treating mares with bacterial uterine infections.

Segabinazzi L, Friso A, Correal S, et al. Uterine clinical findings, fertility rate, leukocyte migration, and COX-2 protein levels in the endometrial tissue of susceptible mares treated with platelet-rich plasma before and after AI. Theriogenology 2017;104:120–126.

2. Ciprofloxacin as Treatment Option for Gram-Negative Bacterial Endometritis

Veterinarians report that antibiotic resistance, particularly of Gram-negative organisms (a certain class of bacteria), has increased over the past several years. One family of antimicrobials, fluoroquinolones, has excellent Gram-negative activity, so “it would be really nice if we could have a fluoroquinolone in our toolbox to treat Gram-negative endometritis,” said Turner.

Turner said the current commercially available fluoroquinolone for horses, enrofloxacin (marketed as Baytril), is not safe for intrauterine use (it can induce a severe hemorrhagic ulcerative endometritis). But ciprofloxacin, a metabolite of enrofloxacin, has an identical spectrum, she added, as well as anti-inflammatory properties.

So, researchers from Colorado State University evaluated ciprofloxacin’s efficacy as an alternative to enrofloxacin to treat Gram-negative bacterial endometritis. They infused infected mares’ uteri with 60 mL of an intravenous formulation of ciprofloxacin used in humans. The team observed high concentrations of ciprofloxacin in the uterine lumen and the endometrial tissue 24 hours later. These concentrations were well above the levels needed to effectively kill the four most common types of bacteria that cause endometritis in mares. They noted little to no evidence of inflammation or other adverse effects.

“So ciprofloxacin right out the bottle might be an option for the treatment of infectious (bacterial) endometritis in mares,” said Turner, adding that it should not be used as a first-line drug (“This is a big gun and should be reserved for resistant organisms only.”) and reminding attendees that this study involved extra-label human products.

Trundell D, Ferris R, Hennet M, et al. Pharmacokinetics of intrauterine ciprofloxacin in the mare and establishment of minimum inhibitory concentrations for equine uterine bacterial isolates. J Equine Vet Sci 2017;54:54–59.

3. Can Progestin and Estrogen Levels Help Identify Problem Pregnancies?

In this study out of Japan, researchers evaluated the use of maternal blood plasma progestin and estrogen concentrations to help identify problem pregnancies. Progestins (hormones related to progesterone) and estrogens (hormones related to estradiol 17-beta) normally increase significantly during mid- to late gestation in mares carrying healthy pregnancies. The researchers took blood samples from nearly 500 pregnant mares every month, tested hormone levels, and determined whether the mares showed clinical signs of problems (e.g., premature udder development, vulvar discharge, abnormal estrogen or progestin values), delivered healthy foals, or experienced foal loss. They found that:

  • Progestin and estrogen concentrations on Days 241-320 of gestation differed significantly between mares that delivered healthy foals and mares that lost their foals;
  • All mares with improved progestin or estrogen concentrations after treatment for clinical signs of a problem delivered healthy foals;
  • When hormone concentrations worsened after treatment, the foal-loss rate was higher if treatment began Days 201-290 of gestation. If treatment began after Day 290, then foals were usually normal despite the worsening hormone values; and
  • Mares with high progestin and low estrogen concentrations were likely to deliver aborted/dead foals mid- to late gestation.

Based on their data, the researchers created a chart with recommended normal values for progestins and estrogens in 20-day increments throughout late gestation. “It gives us a potential diagnostic assay to identify problem pregnancies,” said Turner. “And it shows that serial monitoring of these hormones can be used to determine treatment efficacy and make you better prepared to prognosticate as to whether that pregnancy is likely to be successful.”

She cautioned, however, that while progestin and estrogen testing has an excellent negative predictive value (meaning when estrogen and progestin were normal, there was a greater than 95% chance that the foal was fine), its positive predictive value is not great (when progestin or estrogen levels suggested there was a problem, the foal was often born healthy).

“So if you rely too heavily on these hormonal values, you will end up overdiagnosing problems when no problem actually exists,” she said. “Also, because hormonal changes tend to occur late in the progression of a problem pregnancy, these tests may not be the best method of early detection of problems. However, they are likely to be good for monitoring the status of problem pregnancies, particularly following treatment.”

Shikichi M, Iwata K, Ito K, et al. Abnormal pregnancies associated with deviation in progestin and estrogen profiles in late pregnant mares: A diagnostic aid. Theriogenology 2017;98:75–81.

4. Estradiol to Help Treat Placentitis

Researchers from the University of Illinois Urbana-Champaign and Brazil collaborated on a study in which they evaluated the efficacy of various combinations of estradiol cypionate (a long-acting estrogen) and a long-acting form of altrenogest (a progestin related to progesterone, commonly seen in an oral formulation known as Regumate) to treat ascending bacterial placentitis (placental inflammation).

The study horses consisted of one control group of healthy pregnant mares and five groups of pregnant mares in which researchers induced bacterial placentitis by injecting Streptococcus equi subspecies zooepidemicus into the uterus. Group 1 received a traditional placentitis treatment of the antimicrobial trimethoprim-sulfamethoxazole (TMS) and the anti-inflammatory drug flunixin meglumine (FM). Group 2 received TMS, FM, and altrenogest; Group 3 received TMS, FM, altrenogest, and estradiol cypionate; Group 4 received TMS, FM, and estradiol cypionate without altrenogest; and the fifth group was untreated.

The untreated group had a significant increase in dystocias (difficult births), preterm deliveries, and foal loss. All treatment groups benefited from their respective treatments and their foal survival rates were similar to those among the normal control mares. However, the group treated with TMS, FM, and estradiol was the only one with no compromised foals and similar foal birth weights as controls.

“This suggests that the addition of estradiol may benefit mares with placentitis, and you could also imply that the addition of altrenogest did not appear to improve the outcome,” said Turner. “But I think we need larger studies and studies on naturally occurring placentitis. Don’t throw out your altrenogest just yet.”

Curcio B, Canisso I, Pazinto F, et al. Estradiol cypionate aided treatment for experimentally induced ascending placentitis in mares. Theriogenology 2017;102:98–107.

5. Mare and Stallion Factors Affecting Pregnancy Rates

Irish researchers conducted a large-scale study looking at the effects of a variety of mare and stallion factors on per-cycle pregnancy rate (PCPR) and pregnancy loss in a large population of Thoroughbreds. In stallions they found:

  • There was no difference in PCPR whether the mare was the first one bred by a stallion on a given day or the fourth;
  • There was also no difference in PCPR whether the stallion shuttled between hemispheres; and
  • High-usage stallions that had bred more than 21 times in a seven-day period had a 10% decrease in PCPR.

“So it suggests that in this fertile stallion population, you can tell your owners they don’t have to worry if your mare is the last cover of the day; she has just as much a chance of getting pregnant as the first cover of the day,” said Turner.

In mares they found:

  • A significant decrease in pregnancy rate with advancing age—geriatric mares (18 and older) were 2.9 times less likely to become pregnant than mares 8 and under;
  • An increase in pregnancy loss rate with advancing age—geriatric mares were 2.6 times more likely to lose the pregnancy;
  • Barren mares were 1.8 times more likely to lose a pregnancy than maiden mares;
  • A significant decrease in PCPR in mares bred on foal heat (<20 days from foaling); and – No other effect on PCPR, including whether the mare had been diagnosed with and treated for a uterine problem.

“These study results show mare age has the greatest effect on fertility,” said Turner. “We kind of already knew this, but this adds more to your armamentarium when trying to explain to an owner who wants to breed their 21-year-old mare why it could be very difficult. You can tell them that the older mare is three times more likely to not get pregnant compared to when she was younger and, if she does get pregnant, her chances of losing the pregnancy are almost three times higher.”

Regarding breeding on foal heat, “the decrease in pregnancy rate in mares bred on foal heat (about 10%) did not justify a flat-out decision across the board to not breed on foal heat,” Turner said. “They suggested that if a mare is normal it’s still reasonable to proceed with foal heat breeding knowing there is a somewhat reduced chance of pregnancy.”

Lane E, Bijnen M, Osborne M, et al. Key factors affecting reproductive success of Thoroughbred mares and stallions on a commercial stud farm. Reprod in Dom Anim 2016;51:181–187.