Relationships between the ovarian status and superovulatory responses in dairy cattle.

The aim of this study was to determine the influence of follicular profiles over 4 days prior to superovulation on superovulatory responses. Eighty-eight Holstein cows were synchronized by two prostaglandin F(2)α injections given 11 days apart and conventionally superovulated between days 8 and 12 of the estrous cycle with 400 mg Folltropin-V given in decreasing doses over 4 days. Luteolysis was induced by 2 im injections of cloprostenol (2 ml) with the sixth and seventh injections of Folltropin-V. The ovaries of all cows were examined by ultrasonography with a real-time linear scanning ultrasound diagnostic system (Ls-300-A: Tokyo Keiki Co., Tokyo, Japan; 7.5 MHz Transducer) on days -3, -2, -1, 0 (initiation day of the superovulatory treatment=day 0). Data were analyzed by the GLM procedure of the SAS. Animals with a greater diameter of the largest follicle (F1; 13.4 vs 9.8 and 10.1 mm; p<0.007) and with a greater difference in the diameter of the first and second largest follicles (7.6 vs 4.5 and 3.8 mm; p<0.001) had the greater superovulatory response and produced the greater number of quality I embryos. In conclusion, the diameter of the F1 and the F1-F2 follicles were higher over a 4-day period prior to superovulation in animals yielding a high than a medium and a low number of quality I and I+II embryos.