Analysis of covariance was performed to determine the correlation (rxx) between the different sperm variables, calculated from the residual variances (varx and varx , respectively) and covariance (covxx ): rxx’ = covxx/ (varx and varx)0.5. Percentages were transformed to square roots before analysis. The GLM procedure of the SAS statistical package (SAS Institute, Cary, NC) was used for all data analysis.