This work aimed to determine the effect of cysteamine (25, 50, 100 and 200 mM) incorporated during
dilution on frozen thawed buffalo semen quality. Semen was collected twice weekly for 7 consecutive
weeks from three Egyptian buffalo bulls using an artificial vagina. Semen samples were pooled and
extended with a Tris-based extender, cooled, equilibrated and finally frozen in liquid nitrogen. The
diluted semen was evaluated for motility, viability, morphology, plasma membrane and DNA integrity, in
addition to oxidative stress and in vitro fertilizing capability. The post thaw motility and velocity parameters noticeably increased with different concentrations of cysteamine (mainly 100 mM) during
different incubation periods. The post thaw sperm viability and normality significantly (p < 0.05)
improved with concentrations of 50 and 100 mM. Plasma membrane integrity substantially increased at
all concentrations of cysteamine. Cysteamine reduced alanine aminotransferase (at all concentrations),
aspartate aminotransferase (at 25e100 mM), and creatine kinase (at 100 and 200 mM). Cysteamine at a
concentration of 100 mM noticeably enhanced the total antioxidant capacity and glutathione peroxidase
and decreased nitric oxide production. Cysteamine, at concentrations of 100 and 200 mM, increased the
DNA intensity in the comet head (%) and decreased the DNA % in the comet tail. The comet tail length and
moment substantially decreased at concentrations of 50e200 mM. Cysteamine did not affect the in vitro
fertilizing capability of sperm. In conclusion, cysteamine incorporation (mainly at a concentration of
100 mM) in buffalo semen extender showed varying protective effects on different sperm parameters
against cryo-damage; however, it did not affect the in vitro fertilizing capacity of sperm