Follicular development during the progesterone therapy of ovarian acyclicity and ovarian cysts in cows

Follicular development in cows is characterized by the cyclic growth and atresia of antral follicles in 7-10 days interval - follicular waves. Dominant follicle is selected during follicular wave and periodically it undergoes atresia or ovulation. Continual administration of low doses of progestagens commonly used for induction or synchronization of estrus in cows lead to the prolonged growth and maintenance of the dominant follicle. Application of oestradiol supports luteolytic effect of the treatment. Estrus and ovulation occurrs 2-4 days after the treatment. It was suggested that progestagen treatment in cows with ovarian dysfunction would have a similar effect and it would prolong the growth and increase maturity of the dominant follicle which could respond to gonadotropin rebound effect and ovulate there after. Twenty cows with ovarian acyclicity (experimental group A) and 25 cows with ovarian cysts (experimental group C) 50-100 days after parturition were included to the experiment. Cows were treated with progesterone intravaginal device (PRID, Sanofi) for 12 days. Ultrasound examination of the ovaries was performed on the day of PRID insertion (day 0), following 3, 6, 9, 12, 15, 17 and 25 days after. Samples of milk were obtained for determination of progesterone by RIA on day 0, 15 and 25. Various changes were found in ovarian cysts during PRID treatment in group C; e.g. cysts persisted without any response or they underwent luteinization, in some cases they became large or smaller and/or disappeared. The number of small follicles (4-6 mm) varied, the number of medium follicles (7-10 mm) decreased while the number of large follicles (> 10 mm) increased in group A as well as group C during treatment (Figs. 1 and 2). The dominant follicles grew slowly and persisted during treatment. Ovulation occurred in 14 (70%) and 16 (64%) cows until day 5 after treatment and corpus luteum was found in 12 (60%) and 13 (72%) cows on the day 13 after the treatment in groups A and C. Average concentrations of milk progesterone on day 13 after PRID removal in the groups A and C were 5.6 +/- 5.23 and 6.2 +/- 7.12 ng/ml (Tabs. I and II). The results confirm our hypothesis that response of the ovarian follicles to progestagen treatment in most of the cows with ovarian dysfunction is comparable with the cyclic cows. Then PRID application for 12 days represents alternative method of the treatment of ovarian acyclicity and ovarian cysts.