OVARIAN FOLLICULAR DYNAMICS IN NELORE BREED (BOS-INDICUS) CATTLE

The most common beef cattle raised in Brazil is the Nelore breed (Bos indicus). Information obtained by ultrasonography on follicular growth in Bos taurus cattle has been accumulating rapidly. However, there ar e few publications to date on follicular development in Bos indicus br eeds. The follicular dynamics in Nelore heifers and cows during natura l or prostaglandin (PG)-induced estrous cycle were studied. From the d etection of estrus onward, all animals were examined daily by ultrason ography for one (n=35) or two (n=10) consecutive estrous cycles. The f ollicular dynamic in Nelore cattle was characterized by the predominan ce of 2 follicular waves in the cows (83.3%, n=18, P<0.05) and 3 waves in the heifers (64.7%, n=16, P<0.05). Most of the cattle observed ove r 2 consecutive estrous cycles presented the same pattern of follicula r waves in the first and second cycle, and only 30% showed variation i n the number of waves from one cycle to the other. Most of the follicu lar parameters analyzed were not affected by PG treatment or age but w ere altered by follicular waves. Consequently, data on cows and heifer s were combined according to the number of follicular waves. The ovula tory follicle was larger than the other dominant follicles (P<0.05), a nd the ovulatory wave was shorter than the preceding waves (P<0.05). T he interovulatory interval was longer in animals showing 3 waves than those exhibiting 2 waves (P<0.05). Maximum diameter of the dominant fo llicle (around 11 mm) and of the corpus luteum (CL, approximately 17 m m) were smatter than those reported for European breeds. In conclusion , the results demonstrate that although the dominant follicle and corp us luteum are smaller than in European breeds, the follicular dynamics in Nelore cattle were similar to those observed in European breeds an d were characterized by 2 or 3 follicular waves for cows and heifers, respectively, during the natural or prostaglandin-induced estrous cycl e. (C) 1997 by Elsevier Science Inc.