Evaluation of a new progestin (Sa 45.249) in cattle

Daily oral administration of the progestin Sa 45.249 to 80 cycling heifers, at doses ranging from 6 to 14 mg/day and over varying treatment periods (from 8 to 16 days) resulted in all animals in complete estrus inhibition. Irrespective of the dose and the treatment period used, heat and ovulations — as judged by the corpora lutea which became palpable on day 15 of this cycle — occurred between day 2 and 9 after cessation of treatment in 73 of 80 heifers (91%). Neither the daily dose nor the duration of treatment had any discernible effect on the occurrence of heat.This pattern was confirmed in a pilot field trial. From artificial insemination at the first and second heat after treatment, 16 of 21 treated heifers (76%) and 45 of 55 cows (80%) were pregnant. There was no difference in cyclic plasma progesterone levels between heifers treated for 14 days with 10 mg Sa 45.249 and untreated controls, when treatment commenced either on day 5 or 14 of the cycle, with the exception of the delay in the post-ovulatory rise in the latter treatment.