FOLLICULAR DEVELOPMENT AND SUPEROVULATION RESPONSE IN COWS ADMINISTERED MULTIPLE FSH INJECTIONS EARLY IN THE ESTROUS-CYCLE

To determine whether follicular development, superovulation and embryo production were affected by the absence or presence of a dominant fol licle, cows were administered injections of FSH twice daily in the ear ly (Days 2 to 6, estrus = Day 0) or middle stage (beginning on Day 10 or 11) of the estrous cycle. Treatment with FSH early in the cycle sti mulated follicular development in 83 to 100% of all cows from 4 groups evaluated at different times after PGF2 alpha treatment on Days 6 and 7. However, the proportion of cows with > 2 ovulations varied from 31 to 62.5%, indicating that induction of follicular development may occ ur in the absence of superovulation. When compared with cows treated i n the middle of the cycle, no differences were observed in the proport ion of cows with > 2 ovulations (31 vs 20%), ovulation rate (26.0 +/- 6.3 vs 49.6 +/- 25.8), production of ova/embryos (13.3 +/- 3.2 vs 14.4 +/- 3.4), or the number of transferable embryos (8.0 +/- 3.6 vs 5.4 /- 1.5; early vs middle, respectively). The proportion of the total nu mber of embryos collected that were suitable for transfer was greater (P<0.01) in cows treated early in the cycle (60%) than at midcycle (37 .5%) The diameter of the largest follicle observed by ultrasound prior to initiation of FSK treatment in the early stage of the cycle (10.0 +/- 2.0 mm) was smaller (P<0.05) than at midcyle (16.8 +/- 1.3 mm). Th ese results demonstrate that superinduction of follicular development is highly consistent after FSH treatment at Days 2 to 6 of the cycle a nd that superovulation and embryo production are not less variable tha n when FSH is administered during the middle of the cycle. However, su perovulation in the early stage of the cycle may increase the proporti on of embryos suitable for transfer.