A BLOCK OF THE LUTEINIZING HORMONE AND OF OVULATION DESPITE OESTRUS IN ICI 33828-TREATED GILTS

in Reproduction

Summary.

Thirty-five sexually mature gilts were fed either the compound ICI 33828 (100 mg/day) or a control ration on Day 18 of the oestrous cycle (Day 1 = oestrus). At 2, 4 or 6 days after oestrus, gilts were killed and ovarian and pituitary data collected. Treated gilts not showing an oestrus were killed 10 days after treatment was started. Sixty-seven per cent of the treated gilts showed the forthcoming oestrus. A high percentage (75%) of the treated gilts which exhibited oestrus failed to ovulate. The number of follicles was less than would normally be present before ovulation, and pituitary fsh and lh levels were greater in the ICI 33828-treated (non-ovulating) gilts than in controls. Gilts killed 10 days after initiation of treatment had high levels of pituitary fsh and lh, which may explain the occurrence of superovulation in one gilt (> 100 corpora lutea). These gilts, which did not ovulate except for one pig, also had no follicles greater than 6 mm in diameter, indicating that fsh release was blocked by the drug. The lower ovulation rate in the three ICI 33828-treated gilts which ovulated, compared to the controls, was thought to be the result of decreased follicular growth in the treated gilts.

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