[The follicular system of bovine ovaries after estrus synchronization using the luteolytic action of cloprostenol].

Oestrus synchronization was studied in samples from six cows of the Black-Pied Lowland breed. Three cows four to five days from oestrus were used as the control; three animals with marked periodic corpora lutea were given an i. m. injection of 0.5 mg cloprostenol. The eighth day from the administration of the preparation, the ovaries of the cows were excised and, after histological processing in a simultaneous series in a 4mm interval, the preparations were subjected to qualitative and quantitative microscopic evaluation. The structure of non-atretic and atretic follicles was described in different stages of the atretic process. The lymphoid cells of atretic follicles were observed to penetrate into the granulosa membrane. A multiplication of non-atretic tertiary follicles was observed after the administration of cloprostenol. This multiplication was more pronounced on the right ovary where the preceding ovulation had taken place (P less than 0.01). The treated animals, compared with the controls, showed a significant multiplication of tertiary follicles at early atresia and at total collapse atresia (P less than 0.001), whereas the number of follicles with contractive atresia showed a significant decrease (P less than 0.001). The results suggest that cloprostenol can influence follicle population mostly through the stimulation of the growth and ripening of tertiary follicles; its modulation effect seems manifest itself in cooperating relation with gonadotrophic hormones, mainly with the follicular secondary hormone (FSH), in the theory of the complex effect of proteohormones .