RÉSUMÉ
This investigation focuses on analysing the follicular dynamics exhibited during peri-pubertal period in Sahiwal and Jersey crossbred heifers. The aim of the study was to assess first ovulation in the heifers following puberty (N=20; 10 for each breed). Heifers were subjected to alternate day trans-rectal ultrasonography (TRUS) when the diameter of dominant follicle surpassed 9 mm diameter. Transrectal ultrasonography (TRUS) was performed to observe and assess first ovulation in heifers. The size of the first pre-ovulatory follicle in Sahiwal and Jersey Crossbred heifer in peri-pubertal stage was 10.52�13 and 10.15�51 mm, respectively and the corpus luteum attained its maximum size of 13.89 and 11.26 mm, was significantly different (p<0.01) at day 8.6�4 and 8.2�48 in Sahiwal and Jersey crossbred heifers, respectively. The regression of corpus luteum (CL) adjudged by the Colour Doppler initiated on 10.6�4 and 11.0�63 day for Sahiwal and Jersey crossbred heifers, respectively. Some other follicular dynamics parameters i.e. day of wave onset, number of follicles recruited, inter-wave duration along with maximum diameter of dominant follicle, day of maximum diameter, growth rate, length of growth and static phase, duration of static phase and onset of atresia was recorded, however, no significant difference (p>0.05) was recorded between breeds. On an interesting note, the next estrous cycle for heifers did not lead to ovulation despite having follicular size more than10 mm in both the breeds. Conclusion: In peroration, peri-pubertal Sahiwal and Jersey crossbred heifers had notably precocious luteal regression after first ovulation, without subsequent ovulation in next estrous cycle.