[Delayed parturition in sheep by clenbuterol (author's transl)].

The effect of treatment with clenbuterol on lambing during the period from 9 p.m. to 5 a.m. was studied in a field trial in sheep, which was continued for twenty-two days. The date of tupping was not known. The sheep were divided into an experimental and a control group, each numbering 106 animals. Animals of the experimental group were assessed every day at approximately 7.30 p.m., using a system of scoring for the development of udders and vulvae, and were treated with oral administration of 200 micrograms of clenbuterol when the findings suggested that parturition would occur that night. Seventy-nine animals of the experimental group lambed. twelve of them lambing during the night (two of these had been treated in the evening before lambing); of the group of controls, seventy-two lambed, twenty-three doing so during the night (difference significant: P greater than 0.05). The difference in the number of lambings during the night between treated and untreated animals was highly significant (P less than 0.001). Side-effects of clenbuterol were not recorded. The amount of clenbuterol used in the group of controls was: 3.49 tablets/lambing sheep, 5.03 tablets/treated sheep and 5.02 tables/treated and lambing sheep. This high consumption rate is attributed to the fact that the date of tupping was not known as well as to the defectiveness of the criteria on which the decision to treat or not to treat was based.