Sperm evaluation in cryopreserved bovine semen recovered by two selection methods

Previous experiments have established that various semen manipulation techniques are able to increase the qualitative features of the spermatozoa used in different techniques of assisted reproduction, but practically no comparative data on frozen-thawed bovine semen have been found. The aim of this study was to compare the efficacy of two sperm selection methods: centrifugation on Percoll gradient and filtration through a Sephadex ion-exchange column, to improve the recovery of motile and morphologically normal spermatozoa, without inducing sperm damage, from cryopreserved bovine semen samples. Semen samples were thawed and centrifuged on a discontinuous Percoll gradient, or were filtered through a Sephadex G-15-120 column with the addition of ion exchangers. Sperm concentration, percentages of motile spermatozoa, acrosome integrity, superoxide dismutase activity and lipid peroxidation were evaluated in recovered samples and controls. The motility of spermatozoa obtained by Sephadex ion-exchange filtration (88.87 +/- 6.37%) and by Percoll gradient centrifugation (83.00 +/- 6.21%) were significantly greater than that of control samples (60.14 +/- 8.44%). Other results disclosed that both sperm selection methods significantly increased the percentage of intact acrosome and superoxide dismutase activity. In both cases, the number of recovered spermatozoa diminished significantly versus untreated samples. Although the number of recovered spermatozoa was low, these methods were effective to select viable sperm from cryopreserved bovine semen.