Characterization of Mithun (Bos frontalis) ejaculates and fertility of cryopreserved sperm

Abstract

Technologies for conservation and propagation of genetic resources in the Mithun (Bos frontalis), a rare semi-wild bovine species of Southeast Asia. Successful cryopreservation of Mithun semen would provide a potential vehicle to address above issue. To date, information on characteristics of Mithun ejaculates is not available and there are no reports of birth of live offspring using cryopreserved Mithun semen collected using AV method. A study was therefore conducted to (i) characterize the Mithun ejaculate, (ii) investigate the effectiveness of Mithun sperm cryopreservation, and (iii) determine whether artificial insemination using frozen–thawed Mithun sperm can result in live offspring. Semen samples collected from eight fertile Mithun bulls were evaluated for colour, consistency, volume, concentration, mass activity and progressive motility. The freshly ejaculated sperm were also evaluated for morphological abnormalities, live sperm counts, acrosome integrity, membrane stability (hypo-osmotic swelling test; HOST) and DNA integrity. Semen samples of good quality were cryopreserved in liquid nitrogen using Tris–egg yolk–glycerol diluent. Post-thaw quality of the cryopreserved sperm in terms of progressive motility, morphological abnormalities, live sperm counts, acrosome integrity, membrane stability and DNA integrity were assessed. In addition, 16 Mithun cows at estrus were inseminated with frozen–thawed Mithun sperm. Following cryopreservation, the percentage of progressive motility (fresh versus frozen–thawed), live sperm counts, morphological abnormalities, acrosome integrity, membrane stability and DNA integrity were found to decrease (P<0.01) with a motility recovery rate of 74±9%. Mithun cows inseminated with cryopreserved sperm result 75% conception rate and all the conceived cows maintained full-term pregnancy with delivery of live calves.