Abstract :
Two experiments were conducted to evaluate the effects of the administration of 125 mg
rbST at the time of breeding on fertile and subfertile superovulated ewes – in terms of the
ovulation rate, embryo yield and embryonic development. In addition, the effects of the
treatment on the plasma progesterone concentrations and interferon-tau (IFNT) expression
in the embryos were evaluated in the fertile animals. In the first experiment, carried
out on fertile superovulated ewes, the treatment significantly increased the ovulation rate
(p < 0.05) and shifted the embryo distribution towards more advanced stages of development
(p < 0.01). Plasma progesterone concentrations increased faster in the treated ewes,
being significantly different (p < 0.05) between groups at day 6 post-breeding. In the second
experiment, embryonic development was more advanced in fertile, but not in subfertile
superovulated ewes. The expression of IFNT was significantly (p < 0.01) decreased in blastocyst
embryos obtained from rbST treated animals, compared with non-treated ewes. It is
concluded that the administration of rbST to subfertile ewes at the time of breeding does
not stimulate embryonic development as it does when administered to fertile animals.
