Animal Reproduction Science 63 (2000) 127–136 Follicular dynamics during postpartum anestrus and the first estrous cycle in suckled or non-suckled Brahman (Bos indicus) cows G. Henao a,1 , M. Olivera-Ángel b,∗ , J.G. Maldonado-Estrada b,c,2 a Departamento de Producción Animal, Universidad Nacional de Colombia, Medell´ ın, Colombia b Biogenesis-Biotechnology Group, Universidad de Antioquia, AA 1226 Medell´ ın, Colombia c Facultad de Medicina Veterinaria y de Zootecnia, Universidad de Antioquia, AA 1226 Medell´ ın, Colombia Received 19 August 1999; received in revised form 16 May 2000; accepted 18 May 2000 Abstract Brahman (Bos indicus) cows, were selected at 28±10 days after calving and analyzed by real time rectal ultrasonography three times a week, in order to evaluate and compare follicular and corpus luteum development during postpartum (PP) anestrus and the first PP estrous cycle under sylvopastoril conditions. Suckling (S, n=11) or non-suckling (NS, n=5) cows were evaluated in a zone of tropical dry forest (450 m of altitude, mean temperature=27 ◦ C, annual rainfall=1000 mm). Estrous detection was performed twice daily by direct observation. Progesterone was quantified using RIA. From 28±10 days postcalving to resumption of estrous cycles, there were no differences (P>0.05) between NS and S cows for diameter of the dominant or first subordinate follicle, follicular growth rate, or interdominance interval. Silent ovulation, corpus luteum formation and subsequent progesterone concentrations ranging from 0.3 to 9.7 ng/ml, were found in both groups. The first calving to ovulation and calving to standing estrus intervals were shorter (P<0.01) in NS (34.8±5.81 and 41.2±9.03 days) than in S (65±4.82 and 81±6.21 days) cows. Follicular development and progesterone concentrations during the first PP estrous cycle did not differ (P>0.05) between NS and S cows. These results suggest that Brahman cows could have an early PP resumption of follicular recruitment if fed under sylvopastoril system conditions. However, non-suckled cows did have an earlier standing estrus and ovulation than did suckled cows. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Progesterone; Ultrasound; Sylvopastoril conditions ∗ Corresponding author. Tel.: +574-4259110; fax: +574-4259111. E-mail addresses: ghenao@yahoo.com (G. Henao), molivera@catios.udea.edu.co (M. Olivera- ´ Angel), jungmal@catios.udea.edu.co (J.G. Maldonado-Estrada). 1 Tel.: +574-2607333/ext. 158; fax: +574-2300380. 2 Tel.: +574-4259130; fax: +574-4259104. 0378-4320/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0378-4320(00)00173-1