EFFECTS OF TREATMENT WITH BUSERELIN ON PLASMA-CONCENTRATIONS OF ESTRADIOL AND PROGESTERONE AND CYCLE LENGTH IN THE COW

Treatment of cows with 10 mu g of the gonadotrophin releasing hormone (GnRH) analogue, Buserelin (Receptal; Hoechst) 12 days after mating re sults in a 12% improvement in conception rate (Drew and Peters, 1991). We have now investigated the endocrine effects and possible mechanism of action underlying this effect. Treatment of cyclic cows (n=5) with Buserelin on days 11 and 13 did not affect cycle length or plasma con centration of progesterone, but did significantly (P<0.05) reduce plas ma oestradiol concentration from day 12-16. We conclude that the Buser elin treatment acts by causing a fall in plasma oestradiol which resul ts in a reduction in the strength of the luteolytic drive, improving t he chance of an embryo being able to prevent luteal regression.