The aim of the present work was to determine the weaning effect on ovarian activity during postpartum period, 35 and 70 days after parturition, in Charolais cows that calved during spring season in natural pasture condition. Fifteen cows were randomiy assigned to five weaning treatments as the following: nose-plates for two days (TAB 2), for four days (TAB 4), calves removal for two days (TOT 2), or for four days (TOT 4) and neither nose-plates nor calves removal as a control group. Ovarian activity was controlled for eight days from the beginning of the treatments, followed by both daily blood collection for determining progesterone level and heat identification. Ovaries were evaluated by ultrasound and follicles were classified in small (< 3mm), medium (4 a 9mm) and large-size (>10mm). The number of small and medium size follicles did not change during the eight days of examination among the different treatments at 35 and 70 days in one day at least postpartum. The large size follicles population changed at 35 days postpartum amoung treatments (p = 0.0001) and second day group TOT 4 presented a increase on large siz.e follicle population on second day, decreasing after fifth day by ovulations. The other treatments did not change on different days. At 70 days postpartum, the large size follicles population changed on TAB 2 (p = 0.05) and TOT 4 (p = 0.013), showing a quadratic distribution. There was an animal effect inside treatments (p = 0.0001). Considering the data, it is possible to conclude that weaning with nose plates for two days at either 35 or 70 days postpartum do not change follicular dynamic. The nose plates for four days do not change follicular dynamic at 35 days postpartum but induce an increase in large siz,e follicle population and ovulation at 70 days. The calves removal also induce an increase in large size follicles for 4 days at 35 and 70 days postpartum but do not change follicle dynamic for 2 days.
postpartum anestrus; weaning; follicle dynamic
