Based on previous assessments on stallions, 40 ejaculates of 20 Duroc boars were split and evenly frozen with a conventional vapour freezing method and two directional, drum and directional, prototype methods using commercial extenders and relative standard procedures. The directional prototype was provided with a double internal setup that allowed the positioning of experimental 2ml flat straws with 1 billion sperm (Flat) in a fixed support, or both classical 0.5 ml paillettes with 250 million spermatozoa and flats in a rotating drum designed so as to ensure a more uniform heat exchange. Preliminary tests for individuation of the most appropriate thawing rate showed beneficial effects (P≤0.05) of thawing the sperm at 50°C for 13 s when compared to 42°C for 20 s, in terms of total motility (42.8±8.4% and 35.6±6.8%, respectively). With regard to freezing/packaging methods, major improvements (P≤0.05) were shown for the drum method with paillettes for total motility (38.6±14.2%) assessed immediately after thawing, when compared with the conventional (29.4±13.3%) and the directional methods with flats (30.2±12.8%), and for total motility (P≤0.01) assessed following incubation for 120 min at 37°C after thawing (24.8±11.6%) with respect to the conventional method (15.6±10.9%). Despite the statistical non-significance of results, both the prototype freezing approaches using the experimental flat straw showed some improvements in functional parameters assessed by cytofluorometry when compared to the conventional method.
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