Recent advances in reproductive endocrinology of the mare

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Abstract
The recent development of radioimmunoassay techniques to determine changes in blood hormone levels has increased our understanding of the endocrinology of the oestrous cycle and pregnancy in the mare. This review describes recent findings concerning the endocrine basis and treatment of some common types of infertility. Further evidence supporting the concept that prostaglandin F2∝ is the uterine luteolysin in the mare is discussed. Persistent corpus luteum is now recognized as an important cause of infertility, which may be treated by uterine distension or prostaglandin; recommendations for avoiding treatment failures are presented. The clinical significance of recent findings on the effectiveness of HCG in hastening ovulation, and on the increase in anti-HCG antibodies after repeated injections of this hormone are also discussed. Although antibiotics successfully control the specific pathogen causing contagious equine metritis, the treatment of common opportunistic organisms with antibiotics appears to give indifferent results. The increased understanding of the role of sex steroids in susceptibility to uterine infection seems likely to lead to improved methods of control. Although stimulation of folliculogenesis and ovulation in seasonally acyclic mares is possible using extracts of equine pituitary glands, this treatment is impractical on a clinical scale. Gonadotrophin-releasing-hormone provides a more physiological method of stimulation, and results of recent experiments using this hormone are reviewed. In the pregnant mare, recent studies have shown that the “pregnancy signal” to the mare may be the production of oestrogens from the developing blastocyst from Day 14. Measurement of PMSG as an aid to pregnancy diagnosis is evaluated, and the use of progesterone supplementation to prevent abortion is discussed.