Influence of repeated prostaglandin F2 alpha injections on the ovarian function in the heifer

This study was carried out in order to mimic the postpartum release of prostaglandins. Twenty-five mg PGF2 alpha was given intramuscularly three times daily from day 9 of the oestrous cycle during a period of 15 days in three heifers. Endocrine patterns related to ovulation and corpus luteum formation were determined. Blood samples were collected every second day during the cycle prior to treatment, before each injection during the treatment period and daily during the post-treatment cycle. Plasma samples were analysed for progesterone and oestradiol-17 beta. Palpation per rectum and realtime, B-mode ultrasound scanning of the reproductive tract were carried out once daily. During the period of treatment, ovulation occurred every time after the animals were in oestrus correlating with peaks of oestradiol-17 beta and with an inter-ovulatory interval of 6-7 days. No clear structure of a corpus luteum developed after these ovulations and progesterone levels remained low (less than 1 nmol/l) until the end of the treatment period.