Effect of certain additives in the diluter on post-thaw recovery rate of bovine semen

Semen ejaculates (forty eight, 12 each from 2 Murrah, 2 HF and 2 crossbred bulls) were frozen in presence and absence of two concentrations each of ascorbic acid (an antioxidant), caffeine (metabolic stimulator), chloroquine diphosphate and chlorpromazine HCl (membrane stabilizers). Post thaw quality of semen was assessed using motility, intactness of acrosome and two in vitro fertility tests i.e., cervical mucus penetration test (for functional integrity) and hypo-osmotic swelling (HOS) test (for structural integrity) of fresh as well as frozen semen. Both the concentrations of all the four additives improved post-thaw motility, per cent intact acrosome, per cent HOS positive sperm and sperm penetration distance traveled by vanguard spermatozoa in cervical mucus, as compared to control (without any additive). However, out of two concentration, ascorbic acid in the concentration of 10mM, caffeine in the concentration of 7mM, chloroquine diphosphate in the concentration of 0.54mM and chlorpromazine in the concentration of ^{– 4} M in the diluter were significantly better (in improving post-thaw quality) than the other concentration of these additives respectively, being 15 mM, 10.5mM, 0.81mM and ^{– 5} M. The improvement in the post-thaw quality of semen was recorded for all the three breeds. A significant improvement in the penetration distance traveled by vanguard spermatozoa in the post-thawed semen (after incorporation of additives in the diluter) coupled with significantly higher percentage of spermatozoa responding to the hypo-osmotic solution is indicative of reducing structural and functional damage to sperm cells during freeze-thaw stress. Addition of these additives, therefore, might prove beneficial in maintaining the fertilization potential of frozen thawed spermatozoa.