Ovarian response of prepubertal Murrah heifers to exogenous GnRH

The aim of the current study was to evaluate the ovarian follicular response to GnRH at two dose levels in prepubertal Murrah buffalo heifers during hot-humid months. Heifers received 10 μg (Group A, n = 7) or 20 μg (Group B, n = 6) of GnRH during the growing phase of the dominant follicle (DF > 6 mm), as identified by pretreatment regular ultrasound scanning. A similar dose was repeated approximately 30 days later, again coinciding with another growing DF. Post-treatment ovarian activity was studied by alternate day transrectal ultrasonography until 25 days post-second GnRH. In both groups, three types of response were recorded: formation of a corpus luteum (CL), luteinization of the follicle wall, i.e. luteinized follicle (LF) or no response (NR). Pooled data at GnRH injections revealed that the DF diameter in relation to the type of response in Group A heifers was, NR: 6.83 ± 0.17 (n = 3), LF: 8.10 ± 0.67 (n = 6) and CL: 8.88 ± 0.96 mm (n = 5), while respective values in Group B heifers were 8.68 ± 0.44 mm (n = 4), 9.37 ± 0.46 (n = 6) and 8.95 ± 0.55 mm (n = 2). The pattern of response was more evident in Group A but unpredictable in Group B. Corpora lutea developed in response to both the GnRH injections were short-lived. Mean maximum diameter of LFs in Groups A and B were 16.07 ± 0.99 and 16.58 ± 1.20 mm respectively and wave duration of these follicles in both groups was 23.33 ± 1.67 and 25.33 ± 1.12 days, respectively. None of the heifers commenced cyclicity following regression of the CL or LF.