The objectives of this study were to investigate the effectiveness of ultrasonography in monitoring ovarian activity by examining follicular growth and regression and studying the correlation between corpus luteum (CL) measurements and plasma progesterone (P4) concentrations, and to compare high-and low-production genetic lines of dairy cows regarding endogenous bovine somatotropin (bST) and milk production effects on follicular wave patterns, size and number of follicles, CL growth and plasma P4 concentrations during the estrous cycle monitored by ultrasound. Seventeen multiparous lactating Holstein cows were divided into two groups, a low-production group (control group, n=9) and a high-production group (select group, n=8). Ovaries were examined daily from the day after estrus until the subsequent estrus by ultrasonography to monitor follicular and luteal dynamics. Nine of the 17 estrous cycles investigated in this trial had two follicular waves with an estrous cycle length of 22.2±0.4 days with a ovulatory (Graafian) follicle (18.1±0.4 mm), while 8 cycles had three follicular waves with an estrous cycle length of with a ovulatory (Graafian) follicle (18.1±0.4 mm), while 8 cycles had three follicular waves with an estrous cycle length of 24.5±0.7 days with a Graafian follicle (16.0±0.9 mm). The average length of the 2-wave estrous cycle was significantly shorter (P

The objectives of this study were to investigate the effectiveness of ultrasonography in monitoring ovarian activity by examining follicular growth and regression and studying the correlation between corpus luteum (CL) measurements and plasma progesterone (P4) concentrations, and to compare high-and low-production genetic lines of dairy cows regarding endogenous bovine somatotropin (bST) and milk production effects on follicular wave patterns, size and number of follicles, CL growth and plasma P4 concentrations during the estrous cycle monitored by ultrasound. Seventeen multiparous lactating Holstein cows were divided into two groups, a low-production group (control group, n=9) and a high-production group (select group, n=8). Ovaries were examined daily from the day after estrus until the subsequent estrus by ultrasonography to monitor follicular and luteal dynamics. Nine of the 17 estrous cycles investigated in this trial had two follicular waves with an estrous cycle length of 22.2±0.4 days with a ovulatory (Graafian) follicle (18.1±0.4 mm), while 8 cycles had three follicular waves with an estrous cycle length of with a ovulatory (Graafian) follicle (18.1±0.4 mm), while 8 cycles had three follicular waves with an estrous cycle length of 24.5±0.7 days with a Graafian follicle (16.0±0.9 mm). The average length of the 2-wave estrous cycle was significantly shorter (P