The LH receptor (LHr) present in ovarian follicle cells is essential for the biological response due to its binding to the ligand (LH). The events following the LH surge are related to the presence of LHr and its affinity to LH. Studies on LHr gene expression in theca and granulosa cells from bovine follicles have demonstrated the presence of at least four isoforms of LHr mRNA by alternative splicing. Two of the four detected isoforms have an open reading frame (ORF) and can be translated to functional proteins (receptors coupled with G protein) with different affinities to their ligands (Robert C et al. 2003 Reproduction 125, 437–446). From those two isoforms with ORF, one (full) has affinity to both LH and hCG molecules, whereas the second isoform (with deletion of exon 10) has affinity to hCG only. Recently we have detected the same four isoforms described by Robert et al. in both granulosa and theca cells from abattoir. Based on this information, the present study tested the hypothesis that, in cows superstimulated with FSH, administration of both LH and hCG, as an attempt to stimulate any variety of LH receptor present in the follicles, would result in improvement of oocyte quality and/or increase in ovulation rate. Nelore cows (Bos taurus indicus) were superstimulated according to the protocol termed P-36 (Barros CM et al. 2003 Theriogenology 59, 524 abst), and embryos were flushed 7 to 8 days after inducing ovulation. Ovulation was induced with LH (pLH, 12.5 mg, i.m.; Lutropin, Vetrepharm, London, Ontario, Canada; Group 1) or both LH (12.5 mg) and hCG (1500 IU, i.m.; Choragon, Ferring GmbH, Kiel, Germany; Group 2). Superstimulation protocol and embryo transfer were performed simultaneously on both groups. Mean (± SEM) of total structures, viable embryos, and viability rate were: 12.4 ± 2.36, 10.0 ± 2.38 and 80.8% (Group 1, n = 8 flushings) and 12.2 ± 2.03, 8.9 ± 1.66, and 73.1% (Group 2, n = 14); there was no significant difference between groups (P = 0.96; P = 0.71 (ANOVA), and P = 0.18 (Fisher's Exact Test), respectively). In a subset of embryos (excellent, good, fair, and poor qualities) transferred without freezing, the pregnancy rates for groups 1 and 2 were 41.7% (25/60) and 56.9% (37/65), respectively (P = 0.11, Fisher's Exact Test). The overall pregnancy rates from embryos of excellent, good, and fair qualities were 46.3% (25/54) and 58.9% (33/56), respectively for Groups 1 and 2 (P = 0.25). When only embryos of good, fair, and poor qualities were pooled, the pregnancy rates were 18.8% (06/32) and 60.0% (30/50), respectively for Groups 1 and 2 (P = 0.0003). It is concluded that simultaneous administration of LH and hCG to induce ovulation in superstimulated animals did not alter production of viable embryos or viability rate. However, the use of hCG in addition to LH administration could be beneficial for embryos of good, fair, and poor qualities.

Nogueira has a fellowship from FAPESP (São Paulo).