The effect of recombinant GH treatment on ovarian growth and atresia in sheep

This study investigated the effect of recombinant bovine GH (rGH) on follicle development and LH secretion patterns in ewes. In Experiment 1, 20 ewes (n=10/group) synchronized with progestagen sponges on Day 0 received either a 7 d period of rGH treatment starting on Day 4, or acted as controls. On Day 11, all ewes were unilaterally ovariectomized. Follicles in the excised ovary were characterized on the basis of size, health status and rate of granulosa cell proliferation. Circulating levels of LH, GH, IGF-1 and insulin were monitored. Compared to controls, rGH treatment significantly increased the number of healthy follicles >2.0 mm, reduced the number of 0.25 to 0.5-mm follicles and reduced the number of 0.8 to 2.0-mm early atretic follicles. GH treatment also reduced the mitotic index of 0.25 to 0.5-mm follicles. Recombinant GH treatment had no effect on LH secretion patterns, but plasma GH, IGF-1 and insulin levels were increased in rGH-treated ewes. Because rGH treatment may have had an anti-atresia effect in Experiment 1, the hypothesis for Experiment 2 was that rGH treatment could maintain follicle development beyond 2.5-mm diameter in bovine follicular fluid (bFF)-treated ewes. Forty ewes (n=10/group) were synchronized with progestagen sponges. Starting 5 d after sponge insertion, ewes were treated for 6 d with rGH, bFF, rGH plus bFF, or acted as controls. On Day 12, ewes were sacrificed, and follicles were dissected out of their ovaries and assessed on the basis of size. FSH concentrations were assessed on Days 7, 9 and 11. GH treatment alone significantly increased the number of 2.5 to 4.0-mm follicles compared to controls, whereas no follicles larger than 2.5 mm were present in bFF-treated ewes. In rGH plus bFF-treated ewes, the number of 2.5 to 4.0-mm follicles was similar to controls, but there were less follicles >4.0 mm. GH treatment had no effect on FSH levels, whereas bFF treatment significantly reduced FSH levels. These results expand previous findings that rGH treatment of ewes alters follicle development, but do not suggest that rGH treatment is likely to be of benefit in superovulatory protocols. Furthermore, the data indicate that rGH has an anti-atretic action that is unlikely to be mediated via gonadotropins.