The superovulatory response of Dutch-belted does injected with several standard gonadotrophin preparations twice daily for 3 days at 12, 16 and 20 weeks of age and in adult animals was examined to determine the relationship between age, dose and response. The effects of age and the age × treatment interaction were highly significant (P<0·01). At 12 weeks of age 0·31 mg and 0·50 mg fsh/day resulted in overstimulation without ovulation. Prepriming with progesterone apparently counteracted high fsh levels at this age because 0·125 mg fsh with and without progesterone resulted in 16·8 and 1·8 ovulation points respectively. Similar results were obtained at 16 weeks of age, but at 20 weeks of age the number of ovulation points was lower in the progesterone-treated groups. Adult rabbits responded with a mean of 53·7 ovulations following administration of 0·50 mg of fsh. Overstimulation reduced the rate of egg recovery. This was attributed partially to the effect of endogenous oestrogen production on the rate of egg transport and partially to eggs being trapped in follicles.
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