Synchronisation of oestrus and pregnancy diagnosis in heifers bred in autumn and winter.

The calving rate to artificial insemination following administration of progesterone or prostaglandin was influenced by ovarian activity at the start of the treatment. Significantly more heifers inseminated on a fixed time basis after a 12-day progesterone treatment calved compared to synchronised or control heifers inseminated at a detected oestrus. Administration of 10 mg oestrogen intravaginally by gelatin capsule attached to the progesterone-containing coil or injection of 5 mg oestrogen and 200 mg progesterone at the start of the 12-day progesterone treatment did not influence the oestrous response of calving rate. The accuracy of detection of non-pregnant heifers by oestrous detection, measurement of progesterone in blood 21 days after AI or rectal examination varied from 90 to 93 per cent. However, both oestrous detection and the progesterone test identified significantly fewer non-pregnant heifers. Rectal examination as a method of diagnosing pregnant heifers was significantly more accurate than either of the above.