Response to the first GnRH and pregnancy out come in buffaloes underwent ovsynch and fixed timed artificial insemination

The peculiar reproductive characteristics of the species limit the utilization of artificial insemination (AI) in buffalo. For this reason, in the last years a great attention has been focused on estrus synchronization methods based on fixed timed artificial insemination (FTAI). Among these, the Ovsynch-TAI program has been successfully applied in buffalo. The aim of this study was to assess the response to the first GnRH, prostaglandin and second GnRH in buffaloes synchronized by Ovsynch and subsequent pregnancy outcome. The trial was carried out on 59 buffaloes (138.7±86 days in milk) bred in a commercial farm in the South of Italy. Ten days before the start of the study all the animals underwent clinical and ultrasound examination, to confirm the absence of any gross abnormalities of the genital tract. Synchronization of the estrous cycle was performed by Ovsynch-TAI program which involved the injection of a GnRH agonist on Day 0 (12 μg of buserelin acetate), prostaglandin on Day 7 (5 mg of Dinoprost), and a GnRH agonist again on Day 9 (12 μg). The AI was carried out 16 h after the second GnRH injection, using frozen-thawed semen from bulls of proven fertility. The ultrasound examinations of the ovaries were performed by using a portable Sonoace Pico equipped with a 10 MHz linear transducer adapted for transrectal examination in large domestic animals on Day 0, 1, 7, 9, 10 and 11. All visible antral follicles were recorded and classified into three categories, according to their size: small (diameter < 0.5 cm), medium (diameter between 0.5 and 1 cm) and large (diameter > 1cm). The dimensions of the dominant follicle and the corpus luteum (CL) were further registered. In order to evaluate the characteristics of the CLs, the colour-doppler mode was activated in order to display signals for blood flow in vessels. Pregnancy diagnosis was carried out on 35 days post-AI and the statistical analysis was performed by ANOVA and chi-square test. It was observed that 37 buffaloes (62.7%) ovulated after the first GnRH treatment and showed a functional corpus luteum on day 7. Interestingly, animals that ovulated after the first GnRH injection showed a lower (P=0.08) CL area (22.1±10.1 vs. 28.6±10.3 mm, respectively) and a larger follicle (10.5±4.3 vs. 8.5±3.0, respectively) on day 0. A total of 54 buffaloes (91.5%) showed a functional CL on day 7, although luteolysis occurred only in 50 subjects (84.7%). All the buffaloes (37/37) that ovulated after the first GnRH injection underwent luteolysis. On the contrary, CLs responsive to prostaglandins were recorded only in 59% (n=13) of the animals that did not ovulate after the first GnRH (P<0.01). The response to the second GnRH treatment was very high, since 91.5% of the buffaloes ovulated on the day after FTAI. The ovulation rate was 97.3% (36/37) and 81.8% (18/22) in animals that had either a positive or negative response to the first GnRH injection, respectively. Total pregnancy rate was 59.3% (35/59) on day 35 post-AI. Interestingly, a significantly higher (P<0.01) pregnancy rate was observed in the animals that ovulated after the first GnRH injection (30/37=81.1%) than in those that did not ovulate (5/22=22.3%). As expected, no pregnancies were recorded in animals that did not respond to both the prostaglandin and second GnRH. These results suggest that the response to the first GnRH rather than that to both prostaglandin and the second GnRH may allow to predict the pregnancy outcome after FTAI. In conclusion, the ovulation rate after the first GnRH could be utilized as a preliminary screening of buffaloes to be inseminated, reducing FTAI costs