70 Effect of seasons and additives in Arunachali yak bull semen at different stages of processing and freezing along with fresh semen characteristics

The yak is regarded as one of the world’s most remarkable domestic animals, as it thrives in conditions of extreme harshness and deprivation while providing livelihoods and nutritional security to the highlanders. Although the yak has become a part of the culture of these highlanders, its sustainability is facing several challenges, such as changes in seasonal migration patterns due to impending climate change, forest and rangeland degradation, decline in grazing area, shortage of feed and fodder, modernisation among younger generations, slaughtering for meat, inbreeding, reproductive disorders, etc. Thus, in light of such arising problems, the successful application of quality sperm in various assisted reproductive technologies could address the issues of poor reproductive efficiency along with the propagation of superior yak germplasm. Therefore, the present study was carried out to evaluate the effect of additives and seasons on quality attributes of fresh and post-thawed semen collected from six healthy yak bulls (3–5 yrs of age) maintained at animal herd of Indian Council of Agricultural Research-National Research Centre on Yak, Dirang. A total of 216 fresh semen ejaculates were collected throughout the year in different seasons by standard artificial vaginal method for evaluation of semen attributes, viz: volume, initial sperm motility, sperm concentration, live sperm, sperm abnormality, HOST-reacted sperm, acrosomal abnormality, and intact acrosome. Splitting the ejaculates into two equal parts, the fresh semen group was used for studying semen characteristics, while additives vitamin E (1 mg/mL) and a combination of vitamin E (1 mg/mL) + vitamin C (5 mM/mL) were added to the frozen group to study their effect at different stages of processing and freezing. Most of the positive attributes for fresh semen characteristics were found significantly higher (P < 0.01) in the autumn season, whereas the negative attributes, such as sperm abnormalities (%) and acrosomal abnormality (%), were significantly lower (P < 0.01). The supplementation of vitamin C and the combination of vitamin C + vitamin E showed significantly higher values for most of the positive attributes in comparison with non-supplementation in post-thawed yak semen, and the value for negative attributes was lower during autumn season. It is concluded that a better quality of fresh yak semen could be obtained in the autumn season and effectively cryopreserved in a Tris extender with the supplementation of additives.