In vitro fertilizing capacity and chromatin condensation of deep frozen boar semen packaged in 0.5 and 5 ml straws

The effect of the straw volume employed for semen freezing was studied in 14 ejaculates from seven boars, by evaluating the viability, IVF capacity and chromatin state of spermatozoa. Frozen-thawed semen from 0.5 and 5 ml straws was compared to fresh semen. The chromatin condensation degree was determined by flow cytometry, using propidium iodide as fluorochrome, and the chromatin stability was evaluated by inducing its decondensation with SDS and EDTA. The results obtained for IVF, motility and normal apical ridge (NAR) were: 91.64, 78.14 and 81.47% sperm penetration, 80.78, 68.38 and 70.83% monospermy, 10.86, 9.76 and 10.64% polyspermy, 87.14, 50.71 and 47.86% motility, 79.14, 56.14 and 53.36% NAR, for fresh semen, thawed semen in 0.5 and 5 ml straws, respectively. Frozen-thawed spermatozoa showed significantly increased (P < 0.05) chromatin compactness compared to fresh spermatozoa (55.42, 48.41 and 47.08 fluorescence units (MIFU), for fresh semen, thawed semen in 0.5 and 5 ml straws, respectively). Chromatin was significantly more unstable (P < 0.05) in spermatozoa frozen in 0.5 ml straws (174.7 MIFU) compared to those frozen in 5 ml straws (155.53 MIFU) or to those in fresh semen (149.74 MIFU).