Synchronization of oestrus in heifers with norethisterone

Sixty-five heifers in different stages of the oestrus cycle were fed norethisterone once daily for 17 days at doses of 0.2, 0.6 and 1.0 mg/kg body weight.During treatment swollen vulva, mucus discharge, open and reddened portio and udder enlargement were noted.Norethisterone was effective in suppressing oestrus and ovulation at doses of 0.6 and 1.0 mg/kg. Extremely good heat-synchronization followed the treatment and 98 % of the heifers came on heat within a two-day period. Fifty-five % conceived after the first insemination. In the group receiving 0.2 mg norethisterone per kg, three out of 13 heifers showed psychic heat during treatment. Poor heat synchronization and low conception rate were obtained in this group.A possible effect of cycle stage on heat synchronization was noted only in the 0.2 mg group where a better result was obtained when treatment began in the follicular phase.