3 indicate high correlation among the factors viability, mobility, and sperm membrane functional integrity.
The eigenvalues of the covariance matrix of stan- dardized variables were: 1 2.5990; 2 0.3013; 3 0.0997 (data not shown). In this context, the eigenvalues 1, 2, 3 represent the percentage of total variance (tv) explained by each principal component (PC). Since in our case tv is equal to the number of the standardized variables, that is 3, it follows that 1/ 3*100 86.63%; this means that the first principal com- ponent (whose variance is equal to 1) accounted for 86.63% of the total variance, such that it could be easily interpreted as an overall indicator of sperm quality. Moreover, the eigenvector associated with 1 gave the following coefficients: 1 0.5936; 2 0.5521; 3 0.5855, meaning that our artificial variable, i.e., Sperm Quality, was a weighted mean of the original ones. Evidence that our principal component variable was a valid indicator of overall semen quality was provided by the correlation coefficients observed be- tween the artificial and the original variables, as can be seen in Table 3.
To identify the best cryopreservation procedure in terms of the highest Sperm Quality score we calculated mean scores for each of the 192 treatments. The treat- ment generating the best Sperm Quality score among the 192 tested was the combination: extender Tselutin at a dilution rate 1:4, semen cooling time 60 min; DMA added at 8%; equilibration time before plunging in liquid nitrogen 5 min; drop volume 80 L; and thawing at 75 °C for 10 –12 s. This treatment rendered outcome variables of 32.35% sperm viability, 20.27% sperm