148 Superovulation and embryo production response in oestrus-synchronized Arunachali yak

The Arunachali breed of yak is reared by the Monpa pastoral community of Arunachal Pradesh in India for their livelihood and nutritional security on highland pastures. In addition to fulfilling the basic needs of highlanders, this animal is associated with poor production potential linked to its inherent reproductive problems, including silent oestrus, seasonality, and inbreeding, making yak rearing a less-profitable venture. In the recent past, efforts have been made to improve reproductive efficiency of Arunachali yak through assisted reproductive techniques. However, a few regimens for superovulation have been tried to date with limited success in terms of superovulatory response and embryo recovery. Therefore, the present study was undertaken to evaluate the efficacy of two different doses and regimes of superovulation: Stimufol (400 and 200 µg per animal) and Folligon (1500 and 1000 IU per animal) in Arunachali yak. Twenty-four yaks were allotted in 4 groups (of 6 animals each) and subjected to respective superovulation treatment. Thereafter, the treatment response was assessed in terms of expression of oestrus, interval between treatment and oestrus onset, duration of oestrous, number of corpora lutea and embryos recovered, and analysed using two-way statistical analysis between treatment groups. The results (Table 1) showed a significant (P < 0.01) variation in onset of oestrus after the treatment, whereas other responses did not differ among the groups. Further, the recovered embryos were categorized as excellent, good, fair, and poor according to cell size, shape, texture, and number of vesicles present in the blastomeres; 58.33, 20.83, 8.33, and 12.5% embryos in these categories were recovered, respectively. The overall embryo recovery rate was 30.77%, ranging from 10.53 to 52.38% in different treatment groups. The numbers of embryos recorded were less than the numbers of CL present, showing the possibility of non-availability of all ovulated oocytes for fertilization in the oviduct due to untrapping by the fimbriae. The effectiveness of treatments depended upon the precision of oestrus detection and the time of ovulation. In our study, the variation in onset of oestrus might be associated with poor expression of behavioural oestrus in the treated animals. Based on the present findings, we conclude that all the treatments are effective in superovulation and embryo recovery. However, the use of Folligon at 1500 IU seemed to be comparatively more effective in Arunachali yak. Table 1. Mean (n = 6) average of treatment responses in yak following different superovulatory treatment Variable Treatment Stimufol Folligon 400 µg/animal 200 µg/animal 1500 IU/animal 1000 IU/animal Oestrus response (%) 100 100 100 100 Interval between treatment and oestrus onset (h) 17.67 ± 0.56a 20.83 ± 0.79b 21.17 ± 0.79bc 23.67 ± 1.43c Duration of oestrous (h) 30.33 ± 1.09 28.50 ± 0.99 31.50 ± 1.50 28.83 ± 1.25 Corpora lutea (n) 2.83 ± 1.22 3.50 ± 1.18 3.50 ± 0.67 3.17 ± 0.87 Embryo recovered (n) 0.83 ± 0.83 1.00 ± 0.81 1.83 ± 0.98 0.33 ± 0.21 Recovery rate (%) 29.41 28.57 52.38 10.53 a–cMeans within a row with different superscripts differ P < 0.05.