Effect of different cryo-protectants on the viability of frozen/thawed semen from boars of the Piau breed

The objective of this study was to evaluate the effect of different cryo-protectants (glycerol, dimethylacetamide and dimethylformamide alone or combined and added to lactose–egg yolk extender) on the viability of frozen/thawed semen from the Piau breed as assessed by in vitro testing. Frozen semen samples (n = 20) were used from five male swine. Five different freezing extenders, including 2% glycerol (Group 1 – G), 2% glycerol and 3% dimethylacetamide (Group 2 – GA), 2% glycerol and 3% dimethylformamide (Group 3 – GF), 5% dimethylacetamide (Group 4 – A) and 5% dimethylformamide (group 5 – F), were evaluated. To assess post-thawing sperm quality, sperm motility and morphology were evaluated. Sperm viability was determined using the hypoosmotic swelling test, supravital staining, and a fluorescent assay (carboxyfluorescein diacetate and propidium iodide). The mean total sperm motility of semen immediately after thawing was 46.2 ± 1.3, 57.7 ± 1.5, 53.2 ± 2.1, 51.7 ± 1.2, and 46.5 ± 1.6% for groups 1–5, respectively. Groups 2 (GA) and 3 (GF) had greater motility values (P < 0.05). Fluorescent assay values of 22.3 ± 2.3%, 35.2 ± 3.7%, 30.8 ± 3.4%, 36.6 ± 3.7%, and 26.5 ± 3.8% were obtained for Groups 1–5, respectively, showing that Group 4 (A) sperm had greater viability than those from Group 1 (G), although there was no differences between the other treatments (P > 0.05). The other complementary tests (hypoosmotic swelling test and supra-vital staining) demonstrated that sperm in Groups 2 (GA), 3 (GF) and 4 (A) had the greatest viability and there were no significant differences among these three groups (P > 0.05). The most effective cryo-protectant combinations likely minimized and controlled the deleterious processes that occur in the sperm cell during freezing/thawing, thus improving post-thawing sperm viability. In conclusion, the combination of amides (3%) and glycerol (2%) or dimethylacetamide (5%) alone were more efficient at cryo-protection than glycerol alone for semen freezing in the Piau swine breed.