Late-term hospitalization of mares with high-risk pregnancies warranted – study

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Mare previously assessed as high-risk were found to have significantly more delivery problems than normal.
Mare previously assessed as high-risk were found to have significantly more delivery problems than normal.

Mares with high-risk pregnancies should be hospitalized before birth to ensure specialized care is available should problems arise, researchers suggest.

Researchers in Italy looked at the records of a group of Standardbred mares who gave birth at a veterinary hospital between 2004 and 2020. They found that those previously identified as high-risk did, indeed, have more problems when giving birth.

Aliai Lanci and her fellow researchers, reporting in the journal Animals, found that even a short but abnormal delivery can increase risks to the newborn foal and elevate the chances of complications in the mare.

There are three stages in a horse’s birth. The first stage involves signs of abdominal discomfort and restlessness because of womb contractions. Stage 2 is the phase when the foal is actually delivered, with strong abdominal contractions. The final stage involves the expulsion of fetal membranes.

The study investigated dystocia, involving a prolonged second stage (lasting more than 30 minutes).

“It is a rare event,” the study team said, “but when it occurs it can quickly evolve into a critical situation and lead, in the absence of intervention, to the death of the foal and potentially of the mare.”

Prompt and correct veterinary intervention could preserve not only the health of the foal but also the life and fertility of the mare.

The study team hypothesized that any type of difficulty during the delivery phase could affect the foal’s health, even when this stage lasted less than 30 minutes.

They examined clinical reports on 222 Standardbred mares and their foals hospitalized at the Veterinary Teaching Hospital of the University of Bologna from 2004 to 2020. They found that 165 of the mares had a normal delivery, while 57 had difficulties.

The median stage-2 labour length in normal births was 12 minutes, compared with 20 minutes for the group that had difficulties.

All foals that arrived in normal births were born alive, while in the dystocia group there were eight that were stillborn (14%). The stillbirth rate across the 222 horses was 3.6%.

The overall mortality rate of the 214 live-born foals was 3.3%. The mortality rate among those delivered in a normal birth was 1.8%, while in the dystocia group it was 8.1%.

Overall, there were more mare-related complications following birth, more neonatal diseases, and higher levels of failure in the passive transfer of immunity in foals in the dystocia group.

Among the 222 mares, 32 were assessed as being high-risk pregnancies beforehand. Problems included placentitis, placental edema and placental abruption, an abdominal ventral hernia, rupture of the prepubic tendon, and systemic illness in the mare.

Among only the mares with high-risk pregnancies, the incidence of dystocia was 47%, which was far higher than in the other mares.

The study team concluded that dystocia cannot be considered only a prolonged stage 2 phase in the birth process, since even a rapid but physiologically abnormal delivery can pose a risk to the life of the newborn and cause complications in the mother.

“Considering the level of foaling difficulty can help guide the farm and the practitioner to promptly refer mares,” they said. “Since dystocia is more frequent in cases of high-risk pregnancy, it would be recommended to hospitalize high-risk mares at specialized facilities to ensure assisted parturition, possible surgery and intensive care of both mare and foal.”

The study team comprised Lanci, Carolina Castagnetti and Jole Mariella, from the University of Bologna; and Francesca Perina and André Donadoni, both independent researchers from Verona.

Lanci, A.; Perina, F.; Donadoni, A.; Castagnetti, C.; Mariella, J. Dystocia in the Standardbred Mare: A Retrospective Study from 2004 to 2020. Animals 2022, 12, 1486. https://doi.org/10.3390/ani12121486

The study, published under a Creative Commons License, can be read here

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