Induktion av persisterande gulkropp hos sto : en framtida metod för att dämpa brunstrelaterade störningar?

Abstract: This article starts with a review of the literature regarding the normal reproductive physiology of the mare, normal luteolysis, different causes of prolonged luteal phase and theories behind these. The article also presents a study where it was examined if treatment with human choriongonadotropic hormone (hCG) during the luteal phase induces prolonged luteal phase in mares, thus preventing estrus. The study consisted of two parts: one intensive study of eight mares at the former Department of Obstetrics and Gynaecology at SLU, Uppsala, Sweden and one field study of seven mares at a stud farm 70 km north of Uppsala. The mares in the intensive study were divided in two groups: one with four mares that were injected with hCG in luteal phase when they had a follicle of minimum 30 mm and a second group with four mares that were injected with sodium chloride at the same time. These mares were examined with ultrasonography and blood samples. The blood samples were analyzed for progesterone with a solid phase radioimmunoassay. In the field study only two mares were injected with NaCl and the remaining with hCG. These mares were only observed by ultrasonography and only during a short period after treatment. The study showed that there are several limitations with this kind of treatment to prevent estrus in mares. Only two of the mares in the intensive study treated with hCG showed prolonged luteal activity. Also two of the mares in the field study had signs of a prolonged luteal phase, but this was never confirmed with plasma analysis for progesterone. Some of the mares seldom or never had follicles > 30 mm during luteal phase and those that were treated with hCG and had follicles < 30 mm did not ovulate. Furthermore, if hCG was injected too early in the luteal phase, no ovulations occurred. One mare did ovulate, but the corpus luteum of that ovulation disappeared during luteolysis a few days later. In conclusion, this method to prevent estrous in mares works if you give hCG to mares day 11 or later post ovulation and if there is a follicle of a minimum 30 mm and that this follicle is mature to ovulate.