Induction of Ovulation of Ovulatory Size Non‐Ovulatory Follicles and Initiation of Ovarian Cyclicity in Summer Anoestrous Buffalo Heifers (Bubalus bubalis) Using Melatonin Implants

This study was conducted on summer anoestrous buffalo heifers to monitor the efficacy of melatonin for induction of ovulation and ovarian cyclicity. During pre‐treatment period of 24 days, the ovarian dynamics of five cycling and 10 summer anoestrous heifers was monitored on each alternate day using a transrectal ultrasound scanner. Thereafter, during treatment period, these 10 anoestrous heifers along with additional seven anoestrous heifers were randomly allocated into non‐implanted (n = 5) and implanted (n = 12, one melatonin implant/50 kg, 18 mg melatonin/implant) group. Non‐implanted heifers were monitored on each alternate day till the confirmation of second‐ovulation in implanted heifers. Pre‐treatment period revealed the presence of dominant follicles in anoestrous heifers which attained the diameter comparable with ovulatory follicles of cycling heifers but failed to ovulate and regressed. Between 6 and 36 days (15.3 ± 2.9 days) post‐treatment, all the implanted heifers (p < 0.05) exhibited ovulation of dominant follicles; however none of the non‐implanted heifers ovulated during the corresponding period. The first‐interovulatory period in implanted heifers ranged between 8 and 28 days (18.0 ± 1.8 days). The implanted heifers with short (≤16 days) interovulatory period had short‐lived corpus luteum (CL) that had smaller diameter and secreted less progesterone (p < 0.05). The diameter of CL was large (p < 0.05) and plasma progesterone was high (p < 0.05) following second‐ovulation compared with first‐ovulation in implanted heifers. In conclusion, using melatonin implants, ovulatory size nonovulatory follicles observed in summer anoestrous buffalo heifers can be successfully ovulated to initiate ovarian cyclicity.