Impaired final follicular maturation in heifers after superovulation with recombinant human FSH

The aim of this study was to investigate whether human FSH without contamin ating LH can exert a normal superovulation response in cows. One group of h eifers (n = 9) was stimulated with recombinant human FSH (rhFSH), an FSH so urce without any LH activity, and another group (n = 9) was treated with eq uine chorionic gonadotrophin (eCG), an FSH source with high LH activity. Da ily transrectal ultrasonography showed that eCG- and rhFSH-stimulated heife rs (n = 9 per group) had the same follicular growth characteristics and equ al numbers of follicles > 8 mm in diameter after 3 days of stimulation. The treatment groups differed considerably in steroid production: rhFSH-treate d heifers produced much lower oestradiol concentrations than did eCG-stimul ated heifers during the first days of stimulation and much lower progestero ne concentrations in the period after the LH surge. During the 27-35 h afte r prostaglandin injection, rhFSH-treated heifers had fewer LH pulses than d id eCG-treated heifers (0.3 versus 3.0 per heifer, respectively; n = 3 per group). All rhFSH-treated heifers (n = 6) underwent a preovulatory LH surge , but this occurred significantly later than in the eCG-treated heifers (n = 4; 39.4 +/- 1.9 h versus 47.1 +/- 1.5 h in rhFSH- and eCG-treated heifers , respectively). Multiple ovulations occurred in only three of six rhFSH-tr eated heifers, but in all four eCG-treated heifers with an LH surge. At 24 h after the LH surge, the percentage of metaphase II stage oocytes with cor tical granules distributed close to the oolemma was significantly lower in the rhFSH group (7.3%) than in the eCG group (55.9%). In conclusion, final follicular maturation is impaired in heifers treated with rhFSH, which migh t be due to the combination of a lack of LH activity in the gonadotrophin p reparation and the severe suppression of LH pulsatility.