Dinámica folicular posparto y comportamiento del amamantamiento en razas Angus y Criolla Argentina

To determine the differences in the physio-logical processes that affect the postpartum reproductive performance, follicular dynamics, postpartum cyclicity resumption and suckling behavior were studied in cows of breeds with enhanced reproductive performance (Angus) and poor reproductive performance (Criolla Argentina) in two experiments. In experiment 1, ovarian follicular dynamics was monitored daily by transvaginal ultrasonography in 6 suckled Angus cows and 6 suckled Criolla Argentina cows, from day 30 postpartum to either 90 days after calving or when the second ovulation was detected whichever came earlier. Simultaneously suckling behavior was observed daily for 6 hours at 18 stages of lactation. In each observation, the frequency (number of suckling bouts), average duration of each bout (minutes) and total time spent in suckling (minutes/6 hours), were recorded. In experiment 2, the return to cyclicity was monitored weekly by transrectal ultrasonography in 20 suckled Angus cows and 19 suckled Criolla Argentina cows, from day 30 postpartum until either the observation of the first corpus luteum or until day 90 postpartum. In both experiments, the changes in body weight of cows and calves were monitored. In experiment 1, body weight was similar between breeds. However in experiment 2, Criolla Argentina cows registered heavier weights. Breeds did not differ in parameters of follicular dynamics, ovulation rate (ovulated cows/total cows), duration of postpartum interval or days to observation of first postpartum corpus luteum. This is the first description of postpartum follicular development in the Criolla Argentina breed. Frequency and duration of each suckling bout for Angus calves were not related to age of the calves. However, in Criolla Argentina calves, the frequency diminished and the duration increased with the increasing age of the calves. Total time spent in suckling was not different between breeds or between observation stages. It is concluded that differences in reproductive performance of these breeds did not seem to be mediated by differences in follicular dynamics. The differences in suckling behavior could not be related to postpartum cyclicity resumption due to the fact that the latter might have been affected by differences in body condition of the cows.