The trial was conducted to study if the temporary infertility in ewes induced by oestrogenic clover, would recover accompanied by a concomitant increase in ovulation rate and/or litter size following their removal to a 'safe' pasture. Romney ewes (N - 155) either grazed on Pawera red clover or Ryegrass-white clover (control) pasture for four weeks. Afterwards all ewes grazed ryegrass-white clover pasture and were mated in 3 groups either at the first, third or sixth week post-treatment. Mean ovulation rate was significantly lower (P<0.05) in the Pawera ewes (1.22 ± 0.06) than in the controls (1.49 ± 0.07) on respective treatments after two weeks of grazing. Ovulation rates in ewes after the 1st, 2nd and 3rd mating cycle were 1.60 ± 0.12, 1.41 ± 0.10, 1.27 ± 0.09 (red clover), and 1.64 ± 0.10, 1.67 ± 0.12, 1.30 ± 0.90 (control) respectively. Ovulation rate and litter size were similar for the two treatment groups after joining in week 1, 3 or 6 post-treatment (P>0.05). No increase in ovulation rate/litter size in Pawera group ewes was observed over and above those observed in the control ewes within the six week post-treatment period.

M, Anwar, RG Keogh, and MF McDonald

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 235-238, 1994
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