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Ovarian activity in postpartum, early pregnant and norgestomet synchronized dairy cattle Taylor, Christopher C.


Studies to monitor bovine ovarian function with regard to follicular growth and turnover, and corpus luteum (CL) growth and function, were carried out during three different reproductive states: the postpartum anestrus period, early pregnancy and during the artificial control of the estrous cycle with the synthetic progestin norgestomet. Ovarian function was monitored using a combination of ultrasound imaging and progesterone (P₄) profiling. Growth of large antral follicles (> 10mm) was found to commence very early in the postpartum period and ovulation occurred as early as the first week postpartum. Short first postpartum estrous cycles (< 18 days) were observed in a minority of the animals studied (4/10) and the occurance of a short first cycle was not associated with an early ovulation following parturition. Growth of large antral follicles occurred in a wave-like pattern during the postpartum estrous cycles with most cycles being composed of two waves of growth, the second wave resulting in the growth of the ovulatory follicle. A wave-like pattern of growth of large dominant follicles was also seen through the first 60 days of pregnancy. There was no difference between pregnant and non pregnant cows in the size of the dominant follicle found on day 20. In addition no effect of the CL could be found on the side on which the dominant follicle was found, it was as likely to be on the ipsilateral ovary to the CL as on the contra lateral. The gonadotrophin ihibitor norgestomet did not effect follicular dynamics in the presence of the CL, however in the absence of a CL the dominant follicle present was maintained for the duration of the norgestomet treatment and then went on to ovulate upon norgestomet removal. In addition there was no new growth of antral follicles in the absence of a CL. Norgestomet did not effect the temporal relationship between the onset of standing estrus, the LH surge and ovulation. The results of the three studies suggest that a wavelike pattern of growth of large antral follicles is a characteristic of the bovine ovary regardless of the reproductive state.

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