Clinical Signs and Hormonal Changes in Dairy Heifers after Induction of Parturition with Prostaglandin F_2α

Parturition was induced in 12 dairy heifers with prostaglandin (PG) F_2α, about 2 weeks before the expected time of calving. Eight animals gave birth after two injections (group 1), three animals needed more than two injections (group 2) and one animal (cow no. 740) required one injection. All animals in groups 1 and 2 had retained foetal membranes and the time needed to induce parturition was 59 + 7 and 149 ± 10h, respectively. As cow no. 740 did not have retained foetal membranes and calved 24 h after one PGF_2α injection, it was excluded from the results. Udder distension and relaxation of the pelvic ligaments could predict the calving to within 12 h. Furthermore, the pre-calving drop of body temperature could predict the time of parturition to within 16 h. The total white blood cells and polymorphonuclear cells were at their highest values on the day preceding parturition whereas mononuclear cells had a tendency to increase 3 days after calving. Increased levels of haemoglobin were found at the time of parturition, whereas, plasma-calcium levels significantly decreased after parturition (P < 0.001). Progesterone levels markedly decreased after the first PGF_2α injection and reached 2 nmol/1 at the time of parturition. Plasma levels of oestradiol-17β reached the peak at the time of parturition, whereas, the highest levels of the PCF_2α metabolite and cortisol were recorded 16 h after calving.