EN
The development of the yellow body and ovarial vesicles was evaluated in 20 cows during an entire oestrus cycle (group II, n = 9) and an oestrus ended by pregnancy (group I, n = 11) using a linear ultrasonograph (5 MHz). The investigations were performed on the first day of oestrus and then on the 5, 12 and 18 day after oestrus. The maximum diameter of the yellow body was noted on the 12th day of the oestrus cycle. At the same time (depending on the phase of oestrus) 25 (40%) of the yellow bodies possessed a vesicle situated internally. This phenomenon did not affect either the length of oestrus or the effects of insemination. At the same time in the group of pregnant cows the size of the yellow body with a vesicle was on the 12th day significantly larger than in group II (p < 0,05). A large vesicle was observed with a similar frequency in both groups of cows in 30, 50 and 75% of the animals on the 5, 12 and 18 day of the cycle, respectively. The large size of the vesicle observed on the 5th day of oestrus suggests that it is a vesicle which dominates the first period of growth of the ovarial vesicles.