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

The aim of this study was to investigate whether human FSH without contaminating LH can exert a normal superovulation response in cows. One group of heifers (n = 9) was stimulated with recombinant human FSH (rhFSH), an FSH source without any LH activity, and another group (n = 9) was treated with equine chorionic gonadotrophin (eCG), an FSH source with high LH activity. Daily transrectal ultrasonography showed that eCG- and rhFSH-stimulated heifers (n = 9 per group) had the same follicular growth characteristics and equal numbers of follicles > 8 mm in diameter after 3 days of stimulation. The treatment groups differed considerably in steroid production: rhFSH-treated heifers produced much lower oestradiol concentrations than did eCG-stimulated heifers during the first days of stimulation and much lower progesterone concentrations in the period after the LH surge. During the 27-35 h after prostaglandin injection, rhFSH-treated heifers had fewer LH pulses than did 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-treated 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 cortical 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 might be due to the combination of a lack of LH activity in the gonadotrophin preparation and the severe suppression of LH pulsatility.