The Non-Pregnant Mare: 10th International Symposium on Equine Reproduction Recap

The 10th International Symposium on Equine Reproduction July 26-30 at the University of Kentucky was presented in four sessions: the non-pregnant mare, the stallion, conception and early development, and the pregnant mare and perinatology. Dale Paccamonti, DVM, Dipl. ACT, professor and head of the department of veterinary clinical sciences, school of veterinary medicine at Louisiana State University, recaps the non-pregnant mare session.

  • A number of papers examined the transitional period (between diestrus and regular estrous cycles) and ways to make mares cycle earlier in the year. A study from the labs of Xavier Donadeu, DVM, PhD, and Stephanie Schauer, PhD, et al. reported that administration of purified equine luteinizing hormone every 12 hours in early transitional mares stimulated the growth of follicles that could be induced to ovulate with the hormone human chorionic gonadotropin (hCG). A different approach was taken by Simon Staempfli, DVM, Dip ACT, Dip ABVP Equine, MRCVS, et al., in which mares in early and late spring transition were given a single dose of long-acting progesterone and found that while there was no effect on mares in early transition, 83% (10 out of 12) of mares treated in late transition ovulated within 10-24 days of treatment versus 25% (three out of 12) of nontreated mares. Further work with a larger number of mares will need to be performed to reaffirm this success.
  • Working with mares during the normal breeding season, David Beehan, DVM, examined serum progesterone levels after hCG treatment to determine if the levels could be used to predict ovulation. Mares receiving hCG had significantly higher progesterone 24 hours after ovulation than mares that did not receive hCG; however, these levels were not useful to predict ovulation.
  • A paper by Dominik Burger et al. examined mate choice by mares. Studies in mice and humans have demonstrated that mating preferences are influenced by the major histocompatibility complex (MHC). Mice and humans tend to choose a MHC dissimilar companion, which is believed to help avoid inbreeding and increase chances of survival of offspring. In the study, free-roaming mares were placed one at a time in a barn with six stabled stallions. The mare was allowed to choose her preferred stallion, who was then removed from the stable. She was then allowed to choose her preferred stallion out of the remaining stallions, who was then removed, and so forth until only two stallions were left. The mares were tested in estrus and in diestrus (when the mare is not cycling) and with or without their vision blocked. The mares were then compared to the stallions on the basis of MHC. The mares choice varied significantly based on the stage of cycle when tested. During diestrus choice was not related to MHC differences, but during estrus, there was a tendency for mares to pick MHC dissimilar stallions.
  • Two reports took a closer look at the uterine lining. Robert Causey, DVM, PhD, et al. looked at the uterine epithelium and found an alteration in chronically infertile mares. One of his aims was to clearly define criteria for differentiating normal versus abnormal. Peter Morresey, BVSc, Dipl. ACT, Dipl. ACVIM, et al. used scanning electron microscopy to examine ciliated endometrial cells from reproductively normal mares and from mares with delayed uterine clearance. Cilia are an essential component of the clearance mechanism in the respiratory and reproductive tracts, acting somewhat like a broom to sweep the lining clear of debris. This study found the pattern of distribution of ciliated cells was different between normal mares and those with delayed clearance.
  • Ryan Ferris, DVM, et al. presented the results of their work developing a new tool to detect bacteria in the uterus. They developed a PCR to detect the presence, and identify the strain, of bacteria from a uterine swab, cytology (examination of the cells), or lavage sample. The PCR might provide a rapid test for identifying bacteria, yeast, and fungi found in the uterus.

Other studies included:

  • Ester Botha et al., examined the reversibility of gonadotropin-releasing hormone (GnRH) vaccination to suppress ovarian activity in a large group of mares over a two-year period.
  • A study by Carolyn Arnold, DVM, Dipl. ACVS, and Charles Love, DVM, PhD, Dipl. ACT, evaluated oviductal patency in the standing mare.
  • Alejandro Esteller-Vico et al. examined vascular elastosis in the uterus and its effect on uterine blood flow in cyclic mares.
  • Evidence has been mounting that the mare responds differently depending on the type of bacteria that gain entrance into the uterus. Two studies looked at the response of the uterus to infection with either E. coli or Streptococcus zooepidemicus.
  • A paper by Yasuo Nambo, DVM, PhD, et al. examined the effect of extended photoperiod (number of hours of exposure to daylight) on reproductive endocrinology and body composition in Thoroughbred yearlings and weanlings.
  • Juan Cuervo-Arango, LV, MSc, CertVRep, MRCVSab, and John Newcombe, BVetMed, MRCVSa, examined ultrasound images and correlated changes in the endometrial edema score following mating with pregnancy rate in mares.
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