Post-thaw survival and acrosome integrity of spermatozoa of Leccese rams frozen in different seasons with a milk-egg yolk extender

The influence of the period of semen collection on post-thawing survival, motility and acrosome integrity of spermatozoa in Leccese rams was studied throughout an entire year. The year was divided into the seasons: winter and spring (first semester) and summer and autumn (second semester). Semen from 5 adult rams was collected every two weeks by artificial vagina and frozen according to a freezing system based on milk-lactose egg yolk to constitute semen doses of 400 x 10(6) spermatozoa. At thawing, survival and acrosomal status of cells were assessed and the motility of the sperm and their kinetic rating (scale 0 to 5 score) were determined at thawing (0 h), and after 1 and 3 h incubation (37 degrees C). Semen collected during the first semester (winter - spring) of the year showed the highest (P<0.01) proportion of post-thaw live spermatozoa, with the maximum value in winter (P<0.01), and the best acrosomal status of spermatozoa, considered as both total proportion of spermatozoa with acrosome break down and spermatozoa without acrosomes. Acrosome integrity was positively correlated (r = 0.32; P<0.01) with post-thaw sperm viability. Motility of spermatozoa at thawing was not influenced by the period of semen collection. However, after 3 h incubation sperm motility was higher (P<0.01) during the first semester of the year, without a difference between winter and spring. A marked individual ram effect was found on freezability of semen. The results provide evidence that the period of semen collection can influence freezability of spermatozoa in Leccese rams. The best characteristics of spermatozoa were observed during the first semester of the year, corresponding to the sexual hypoactivity season for this breed.