Fertility And Fetal Sexing: Broodmare Questions, Answered

by | 04.17.2018 | 3:12pm

As Thoroughbred foaling season gets into full swing, Central Kentucky fields are filling up with fluffy foals, the majority of which will have had uncomplicated entry into the world. Inevitably though, a small minority of dams may find themselves faced with a dystocia (difficult birthing) and will be whisked away to the hospital for a cesarean section if experts can't assist the mare stallside.

Once the drama is over with mare and foal hopefully back home and thriving, owners may wonder – so, what about next year? Can a mare successfully have another foal after undergoing cervical trauma and surgery?

According to Dr. Charlie Scoggin of Rood and Riddle Equine Hospital, the answer is probably yes – but you'll need to be patient.

Dystocia puts a mare at risk for damage to her cervix, but that's not the only reason a mare could need cervical surgery. Trauma from breeding can cause damage, or the area can develop lesions with age which need repair. These types of damage can sometimes be difficult to find.

“The presentation isn't always classic,” he said. “Some mares may just fail to become pregnant according to ultrasound exams or fail to donate an embryo when you flush them. Other mares may have a repeated history of pregnancy loss at 28 days or 60 days. It takes a fairly careful evaluation of the cervix to identify some of these defects.

“The cumulative effect of all these things is subfertility.”

Speaking at the clinic's annual client education seminar in February, Scoggin showed results from a retrospective study looking at the fertility of mares after a cervical repair. The data, which drew from records of 444 Thoroughbred mares treated between 1995 and 2015, found mares with one or two cervical surgeries were capable of producing a live foal after surgery. Only about 20 percent produced a live foal within a calendar year of their surgery, however, with the likelihood increasing over subsequent years. Mares two years removed from surgery saw their chances of live foal increase to 45 percent.

One thing Scoggin said mare owners should be aware of is the recurrence rate, or the percentage of mares with one cervical surgery who would later require another. His research found a 20 percent recurrence rate for cervical repairs. Mares requiring two or more surgeries had an average of 429 days between surgeries. Unsurprisingly, the more surgeries a mare had to repair her cervix, the lower her chances of producing a live foal became.

Scoggin found two factors impacting the chances a mare with a history of cervical surgery might need another. One was age, which is the cause for a lot of reproductive issues in broodmares. The other was the location of the lesion that prompted surgery.

“A ventral lesion [one on the lower, abdominal-facing side of the cervix] tends to carry a little bit poorer prognosis than those that incorporate the top part of the cervix,” said Scoggin.

Dr. Tom Riddle, one of the co-founders of Rood and Riddle, also fielded audience questions about fetal sexing in horses. It's common for humans to find out ahead of time whether their offspring will be male or female, but Riddle said he's often asked why (besides curiosity) a breeder may want to know.

Fetal sexing for horses can take place between day 55 and day 75 of gestation when the foal's genitalia is starting to form, or between 105 and 110 days, when organ development is farther along and the foal comes back into view after spending time down toward the bottom of the uterus. The process has become very accurate: in thousands of fetal sexing scans, Riddle remembers just a handful of times he has turned out to be wrong.

“I think the primary reason [for fetal sexing] is for valuation of the mare and fetus,” said Riddle. “In today's times, people are really analyzing almost all the data they can get to stay in business, and if they're considering selling their mare the sex of the foal she's carrying will make a big difference in her value.”

Riddle also encounters breeders who will decide a mare's destination for foaling based on the gender of the foal. One of his clients, who is based in Japan, foals out colts in Japan and fillies in Kentucky. He is also aware of future stallion choices being made based on fetal sexing: some owners may send a mare to an expensive stallion in hopes of getting either a filly or a colt and could breed the mare back to him the following year if they don't get what they want on the first try.

Riddle said he has never been asked to terminate a pregnancy based on the determination of a fetal sexing scan.

“It also may be helpful in determining future income. Some people keep all their colts, sell their fillies or vice versa,” said Riddle. “If they have 20 mares and they have a year that most of their mares conceive colts, that's going to affect their future income.”

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