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

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.Uppsatsen börjar med en sammanställning av litteratur som tar upp stons normala reproduktionsfysiologi, normal luteolys och olika orsaker till förlängd lutealfas. I uppsatsen redovisas också en studie där det undersökts om behandling med humant choriongonadotropin (hCG) under lutealfas hos ston orsakar en förlängd lutealfas och på så sätt förhindrar brunst. Studien bestod av två delar: en intensivstudie av åtta ston på f.d. institutionen för obstetrik och gynekologi (numera institutionen för kliniska vetenskaper), SLU, Uppsala och en fältstudie av sju ston på ett stuteri sju mil norr om Uppsala. De ston som ingick i intensivstudien delades in i en försöksgrupp som injicerades med hCG under lutealfas när de hade en follikel > 30 mm och en kontrollgrupp som injicerades med NaCl. Stona undersöktes med ultraljud och blodprover, som analyserades för progesteron. I fältstudien injicerads endast två ston med NaCl, övriga ston fick hCG. Dessa ston studerades med ultraljud under en kortare period efter injektionen. Studien visar att det finns ett antal begränsningar med denna behandlingsmetod med hCG för att förhindra brunst. Endast två av de behandlade stona i intensivstudien visade en förlängd lutealfas. Två av stona i fältstudien visade också symptom på förlängd lutealfas, men detta konfirmerades aldrig med blodprover för analys av progesteron. Några av stona fick aldrig folliklar > 30 mm under lutealfas och de ston med folliklar < 30 mm, som behandlades med hCG ovulerade inte. Inte heller inträffade ovulation om hCG gavs för tidigt under lutealfasen. Ett sto ovulerade tidigt i lutealfas, men den bildade gulkroppen försvann ett par dagar senare i samband med luteolys. Slutsatsen av studien blir att denna metod för att förhindra brunst fungerar om hCG ges till stona dag 11 eller senare post ovulation och om de då har en follikel som är > 30 mm, samt att denna follikel är mogen för ovulation

A preliminary study on the induction of dioestrous ovulation in the mare – a possible method for inducing prolonged luteal phase

BACKGROUND: Strong oestrous symptoms in the mare can cause problems with racing, training and handling. Since long-acting progesterone treatment is not permitted in mares at competition (e.g. according to FEI rules), there is a need for methods to suppress unwanted cyclicity. Spontaneous dioestrous ovulations in the late luteal phase may cause a prolongation of the luteal phase in mares. METHODS: In this preliminary study, in an attempt to induce ovulation during the luteal phase, human chorionic gonadotropin (hCG) (3000 IU) was injected intramuscularly in four mares (experimental group) in the luteal phase when a dioestrous follicle ≥ 30 mm was detected. A fifth mare included in this group was not treated due to no detectable dioestrous follicles ≥ 30 mm. Four control mares were similarly injected with saline. The mares were followed with ultrasound for 72 hours post injection or until ovulation. Blood samples for progesterone analysis were obtained twice weekly for one month and thereafter once weekly for another two to four months. RESULTS: Three of the hCG-treated mares ovulated within 72 hours after treatment and developed prolonged luteal phases of 58, 68 and 82 days respectively. One treated mare never ovulated after the hCG injection and progesterone levels fell below 3 nmol/l nine days post treatment. Progesterone levels in the control mares were below 3 nmol/l within nine days after saline injection, except for one mare, which developed a spontaneously prolonged luteal phase of 72 days. CONCLUSION: HCG treatment may be a method to induce prolonged luteal phases in the mare provided there is a dioestrous follicle ≥ 30 mm that ovulates post-treatment. However, the method needs to be tested on a larger number of mares to be able to draw conclusions regarding its effectiveness