Supplementation of L-tryptophan (an aromatic amino acid) in tris citric acid extender enhances post-thaw progressive motility, plasmalemma, mitochondrial membrane potential, acrosome, and DNA integrities, and in vivo fertility rate of buffalo (Bubalus bubalis) bull spermatozoa

The aromatic amino acid L-tryptophan is an essential and versatile molecule, acts by transferring an electron to free radicals and protects the plasma membrane from injuries. The aim of the present study was to investigate the effects of L-tryptophan in extender on semen quality parameters, in vitro longevity and in vivo fertility rate of buffalo spermatozoa during cryopreservation. Two ejaculates were collected from each bull (n = 2 ejaculates and n = 4 bulls) with artificial vagina at 42 degrees C followed by initial evaluation for volume, motility, concentrations and were diluted in five extenders (C = lacking L-tryptophan, D1 = 25 mu M L-tryptophan, D2 = 50 mu M L-tryptophan, D3 = 75 mu M L-tryptophan, and D4 = 100 mu M L-tryptophan) respectively, and cryopreserved. The experiment was repeated four times (n = 4 replicates). At post-dilution, sperm plasma membrane integrity (PMI, %), supravital plasma membrane integrity (SVPMI, %), hypo-resistivity (HR, %) and acrosome integrity (ACR-I, %) were significantly higher (P < 0.05) in extender supplemented with D4 than control. At post-thawing, progressive motility (PM, %), PMI, SVPMI, HR, ACR-I, and DNA-I of buffalo bull spermatozoa were significantly higher in D4 than control. Sperm in vitro longevity (%) assessed in terms of PM, SVPMI, and ACR-1 were significantly higher in D4 than control. Sperm mitochondrial membrane potential (%) was higher in treated groups than the control. The in vivo fertility rate was significantly higher in D4 than control (60.17% vs. 44.17%, P < 0.05). It is concluded that the supplementation of L-tryptophan in tris citric acid extender improves semen quality parameters, in vitro longevity and in vivo fertility rate of buffalo spermatozoa during freezing and thawing process.