Modulation of postthaw motility, survival, calcium uptake, and fertility of bovine sperm by magnesium and manganese.

Because Mg2+ and Mn2+ are potent stimulators of motility through the stimulation of adenylate cyclase activity, the current study was undertaken to modulate the fertilizing ability of bovine semen by incorporation of various concentrations of those two salts in extenders before freezing. Motility analysis at 6 h in vitro showed a positive effect of MgCl2 in a dose-dependent manner from 0.5 to 5 mM (31 to 50%). Manganese at the concentration of 0.1 mM also supported good sperm motility (53%) compared with that of the control (28%). Although survival was increased, no detrimental effects were seen on the number of sperm that penetrated mucus of cows in estrus. The intracellular Ca2+ concentration of sperm was very different across treatments after thawing; spermatozoa that were extended with 2 mM MgCl2 and 0.5 mM MnCl2 possessed the highest concentrations at thawing. Four hours later, in the presence of Ca, spermatozoa that were extended in 0.1 mM MnCl2 showed the highest uptake. In the presence of Ca and heparin, spermatozoa that were extended in different amounts of Mg showed Ca2+ concentrations that increased in a dose-dependent manner. This effect was negated by glucose. Functional fertilizing capacity was also evaluated by in vitro fertilization, and the different treatments did not show any detrimental effects. In summary, 5 mM MgCl2 and 0.1 mM MnCl2 both have beneficial effects for the maintenance of sperm motility without detrimental effects on mucus penetration and fertilizing ability. Furthermore, these treatments do not prevent subsequent Ca2+ uptake in response to heparin. These in vitro studies are potentially a good sorting system to predict the benefits of extender modifications.