Placentitis was the subject of an in-depth session at the convention. Michelle LeBlanc, DVM, Dipl. ACT, of Rood and Riddle Equine Hospital in Lexington, Ky., set the tone for the session when she told her listeners that, "The single most important cause of premature delivery of a foal is placentitis. It accounts for nearly one-third of late-term abortions and fetal mortality in the first day of life."
She said 90% of placentitis cases stem from bacteria entering the uterus via the vagina, then breaching the cervical barrier.
While the disease is insidious, she said, horse owners and practitioners have the advantage of being alerted by some outward signs, enabling them to begin a treatment to save the foal. Two of the classic tip-offs are vaginal discharge and premature udder development.
The goal of the practitioner, she said, is to manage these mares so that pregnancy is prolonged. "If premature birth can be delayed for a few weeks after clinical signs of placentitis develop," she informed her listeners, "a foal may be born significantly premature, but survive with limited neonatal care."
She discussed a study that took place earlier in her career when she was on the staff at the University of Florida. The goal of the study was to determine whether measuring changes in maternal plasma progestins and determining placental thickness or separation were valid protocols in determining whether placentitis was posing a threat of abortion.
During the study, LeBlanc said, plasma progestin concentrations and transrectal ultrasonography findings were compared between 15 pony mares carrying normal pregnancies and 15 mares that received a cervical inoculation of Streptococcus equi between 270 and 293 days of gestation.
Peter Sheerin, DVM, Dipl. ACT, also of Rood and Riddle, picked up the narrative at that point and noted: Uterine-placental thickness (CTUP, or combined thickness of the uterus and placenta) was measured by transrectal ultrasonography in all mares beginning at 224 days gestation. Experimental mares were scanned weekly until inoculation and every 48-72 hours after inoculation with bacteria. A combined uterine-placental thickness (CTUP) in excess of 1.2 cm was considered abnormal.
All of the control mares in the study, Sheerin said, delivered healthy foals. Only two of the mares innoculated with bacteria delivered live foals; both were somewhat premature but were described as viable and precociously mature.
Sheerin also reported: "Four of the 15 mares with placentitis could not be identified clinically because they did not exhibit a vaginal discharge or precocious mammary development. Fourteen of 15 mares exhibited changes in their plasma progestin profiles. Plasma progestins decreased sharply in the seven mares that aborted within seven days of inoculation and increased in seven of eight mares that carried their fetuses for more than 15 days after inoculation.
"All inoculated mares exhibited histological changes in the cervical star region of the placenta consistent with ascending placentitis," added Sheerin. "Nine of 15 inoculated mares had a combined uterine-cervical thickness in excess of 1.2 centimeters before delivery. Four of the seven mares that aborted less than seven days after inoculation--and two mares that carried for more than 15 days--had CTUP less than 1.2 centimeters."
Sheerin drew these conclusions from the study: "Fourteen of 15 mares were identified when both transrectal ultrasonography and plasma progestin profiles were performed. However, four of the 15 inoculated mares did not exhibit clinical signs. Therefore, ultrasonography and plasma profiles are useful diagnostically only if the mare exhibits either vaginal discharge or premature udder development."
In a later presentation as part of the in-depth series, Margo MacPherson, MS, DVM, Dipl. ACT, of the University of Florida, dealt with treatment protocols for placentitis. In a large clinical study regarding treatment of mares diagnosed with placentitis in Kentucky, she said, investigators examined records of 477 mares. Fifteen were diagnosed with placentitis.
The clinical signs presented included early udder development, vaginal discharge, and increased CTUP. The mean gestational age at diagnosis was 8.6 months.
The mares were treated with a combination of systemic antibiotics--trimethoprim sulfa, ceftiofur, or penicillin and gentamicin--along with pentoxifylline, non-steroidal anti-inflammatory drugs (NSAIDs), and altrenogest (Regumate). The afflicted mares were treated from discovery of the disease until they either aborted or delivered a live foal. Eleven of the 15 diagnosed and treated mares delivered live foals. Birth weights of the surviving foals from mares treated for placentitis, MacPherson said, were similar to foals from non-affected mares.
She also reported on a study that indicated trimethoprim sulfa and pentoxifylline--alone or in combination--can delay pre-term delivery in mares with placentitis.
"Data from these two studies," MacPherson concluded, "suggest that antibiotic and anti-inflammatory treatment may positively impact pregnancy outcome in mares with placentitis."
More information: www.TheHorse.com/ViewArticle.aspx?id=5433.
Caring for the Foals
Fairfield Bain, DVM, Dipl. ACVIM, ACVP, ACVECC, of Hagyard Equine Medical Institute in Lexington, Ky., discussed "Management of the Foal from the Mare with Placentitis."
These foals, Bain said, can range from being extremely early--300 days--with small size and organ function incompatible with life, to a full-sized foal nearer to full-term gestation with minimal effects.
Once a mare is diagnosed with placentitis, he said, it is incumbent upon the veterinarian to inform the owner about potential outcomes. There are a number of cases where humane considerations and economics figure into the decision-making process. The underlying message was that treatment of a premature foal in an intensive care facility can be expensive, with no guarantee of a positive outcome.
"Once the decision is made to allow an affected foal to survive," he said, "it should be considered a 'high-risk' neonate and be treated accordingly. This should include initial laboratory workup and possibly early treatment for birth asphyxia. The physical examination should include assessment of all organ systems--eyes for evidence of hypopyon (an accumulation of pus), lungs for evidence of in utero pneumonia, and placental membranes for patterns of inflammation. Sampling should be done for culture, histopathology, and possibly cytology (cell examination). In many foals born early, orthopedic assessment remains a significant part of the decision process, because incomplete ossification of the cuboidal bones, especially in the hocks, remains one of the most important factors in loss of use, and in some cases eventual euthanasia of affected foals."
The most important element in dealing with an at-risk premature foal, Bain said, involves supportive and nursing care. "The facilities required for this generally include a stall with capability for heating, padded bedding to prevent pressure sores, and, most importantly, the technical personnel to provide continuous monitoring and nutritional support," he said.
Even if the foal survives, it is difficult to predict whether it will have normal growth and development, Bain concluded.
More information: www.TheHorse.com/ViewArticle.aspx?id=5435.
Placental and Post-Mortem Exams
Donald Schlafer, DVM, MS, PhD, Dipl. ACVP, ACVIM, ACT, a professor of comparative obstetrical and gynecological pathology in the college of veterinary medicine at Cornell University, presented a detailed account of how a veterinarian might carry out a post-mortem examination of the equine placenta, fetus, and neonate. Performance of a thorough placental examination, he said, requires a basic understanding of placental anatomy and some familiarity with the gross features found in a normal placenta.
"Two essentials of a thorough gross placental examination," he said, "are 1) that one can distinguish normal features and common artifacts from lesions that may have diagnostic significance; and 2) that one knows how to collect appropriate samples for submission to a diagnostic lab."
Step one when examining a placenta, Schlafer said, is simplified by first finding the cord and carefully unfolding and flattening the three "arms" of the Y-shaped chorioallantoic membrane (the outer membrane in the placenta). One of the first concerns, he emphasized, is to check for completeness because retention of pieces at the tips of the horns is relatively common and can have serious consequences.
The umbilical cord also should be examined to determine if cord torsion has occurred, something that is not uncommon in the horse. Undue twisting of the cord can obstruct blood and urine flow.
When examining a placenta, he said, one of the most important areas is the cervical star, where the foal normally erupts through the placental membranes.
"The chorioallantoic cervical star deserves special attention because it is that part of the placenta that is physically against the inner side of the cervix. Because ascending infections through the cervix are common in the pregnant mare, the cervical star area must be carefully examined and routinely sampled. If the placenta is prematurely separated from the endometrium, the fetus can rupture the chorioallantois in an area that is not the cervical star. This finding and the presence of a markedly congested chorioallantoic membrane in the distal body near the star are important diagnostic features of premature placental separation."
Schlafer then went into detail on what samples should be taken for laboratory analysis and approaches involved in doing a foal necropsy.
He also provided a suggested pathology report form for veterinary use when dealing with an aborted foal.
More information: www.TheHorse.com/ViewArticle.aspx?id=5434.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
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