MODIFICATION BY PROPYLENE-GLYCOL OF OVULATION RATE IN EWES IN RESPONSE TO A SINGLE INJECTION OF FSH

Five experiments were conducted with the objective of developing a met hod to induce superovulation in ewes with a single i.m. injection of F SH. This was achieved by injection of 10 mg FSH-P in propylene glycol at the same time as luteolysis was induced by cloprostenol on day 13 o f the oestrous cycle (day 0 = oestrus). Experiments 1, 2, 3 and 5 were conducted in a single flock of Manchega ewes in Spain during the bree ding season. Ovulation rates were determined at laparoscopy. In Expt I , FSH-P was diluted in saline, and neither 5 mg FSH on day I nor 5 or 10 mg FSH-P on day 13 changed the ovulation rate after cloprostenol tr eatment on day 13. In Expt 2, FSH-P was diluted in propylene glycol an d data were collected over 2 years. Ten milligrams FSH-P, on day 13 on ly increased (P < 0.01) the mean number of corpora lutea to 5.5 compar ed with a control value of 1.5. Five milligrams FSH-P on day 13 only h ad no effect; however, 5 mg FSH-P on day I reduced the mean number of corpora lutea formed in ewes receiving 10 mg FSH-P on day 13 to 2.6 (P < 0.01). Saline and propylene glycol, as vehicles for 10 mg FSH-P, we re compared directly at two times of injection in Expt 3. FSH-P increa sed the mean number of corpora lutea when injected on day 13 in propyl ene glycol (4.7) but not in saline (2.5; P < 0.5). Ovulation rate did not differ between diluents when FSH-P was injected 24 h before clopro stenol (1.3; day 12). Experiments 4 and 5 were conducted to examine po ssible mechanisms by which propylene glycol improved the response to F SH. In Expt 4, conducted during anoestrus in a crossbred flock in West Virginia, concentrations of FSH in plasma were measured for 58 h afte r injection of 10 mg FSH-P in saline or propylene glycol. Propylene gl ycol did not delay the time of maximum concentration of FSH in plasma after i.m. injection (2.7 +/- 0.7 h) when compared with saline injecti on (3.6 +/- 0.5 h). Maximum concentration was reached later when FSH-P was injected s.c. in propylene glycol (7.6 +/- 0.7 h; P < 0.05). In E xpt 5, ovulation rate was greater (P < 0.05) in ewes treated with 10 m g FSH-P in propylene glycol than in ewes treated with FSH-P in saline and an injection of propylene glycol at a separate site. The number of corpora lutea did not differ in ewes treated with FSH-P in saline and in ewes treated with FSH-P in saline and propylene glycol at a separa te site. Thus neither delayed absorption nor an augmentation effect co uld account for the benefit of propylene glycol as a vehicle for deliv ery of FSH to superovulate ewes.