As part of the study into the mechanism by which nutrition influences ovulation rate two trials have been conducted to examine the effect of protein intake on the negative feedback of oestradiol-17Beta (E17Beta) on plasma FSH levels. In Trial 1 three groups of ovariectomised ewes (n=8) fed on a low protein (LP 11%, 10 MJ ME) diet were treated with silastic implants of E17Beta. Four days after implant insertion one group was changed to a high protein (HP 22%) diet while another was treated orally for 10 days with phenobarbital (1 g/d). The E17Beta implants were removed 6 days after treatment started. In Trial 2 groups of ewes (n=6) were given either full (HE) or 1/2 size (LE) implants for 5 days. All ewes were fed on a LP diet but 2 groups were infused abomasally with 100g/d of protein (HP) commencing 3 days before implant. FSH levels were monitored 4 x d throughout both trials and expressed as a percentage of pre-treatment values. In Trial 1 FSH levels were 33% on day 11 after implant with no treatment difference. However after implant removal the values for the LP ewes returned to 100% by day 17 while for the HP and phenobarbital group values remained at 33%. In Trial 2 the levels 4 days after implant insertion were 37%, and 48% for the HE and LE ewes. Again protein treatment delayed recovery following implant removal. These results do not support the hypothesis that the increased ovulation rate following protein supplementation is due to a reduction in negative steroid feedback on FSH levels.
Proceedings of the New Zealand Society of Animal Production, Volume 50, , 97-100, 1990
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