Effect of tetracosactid on post partum cyclicity in cows after induction of parturition with PGP(2 alpha)

Parturition and retention of fetal membranes were induced with PGF(2 alpha) in 3 primiparous dairy cows. Starting on day 12 post partum (PP) the cows were treated with 500 mug i.m. of ACTH-analogue (tetracosactid) every 6 h f or 6 times. Changes in plasma concentrations of cortisol, progesterone and 15-ketodihydro-PGF(2 alpha) were evaluated immediately after treatment. The effects on the resumption of ovarian activity were evaluated by clinical a nd ultrasound examinations and by progesterone and 15-ketodihydro-PGF(2 alp ha) analyses for 56 days after parturition. Treatment was able to induce a statistically significant (p <0.01) similar increase in cortisol and proges terone after both the 1(st) and the 6(th) injections, in all cows. No chang es in 15-ketodihydro-PGF(2 alpha) concentrations were seen after any of the injections of ACTH-analogue. The first corpus luteum (CL) was seen on day 18 PP (cow A), and 28 (cow B) and in both cases it was followed by a normal ovarian cyclicity. No CL was observed during the whole period of study in cow C. Progesterone profiles confirmed these clinical and ultrasonographic findings. The steroid output, especially progesterone, induced by the ACTH- analogue might be a stimulus for the onset of ovarian cyclicity, since 2 of the 3 animals ovulated earlier than expected. These findings point to the fact that interference with the stress system might have a positive effect on ovarian cyclicity. The different pattern of response does however demand further studies.