The influence of antioxidant, cholesterol and seminal plasma on the in vitro quality of sorted and non-sorted ram spermatozoa

In an effort to improve the number of functional spermatozoa following sex-sorting and cryopreservation, the effects on in vitro sperm characteristics of the additives: (i) catalase (pre-sorting); (ii) cholesterol-loaded cyclodextrins (CLCs; pre-sorting); and (iii) seminal plasma (post-thawing) were investigated. For all experiments, spermatozoa (three males, n = 3 ejaculates/male) were processed using a high speed flow cytometer before cryopreservation, thawing and incubation for 6 h. Catalase had no effect (P > 0.05) on post-thaw motility characteristics (as measured by CASA) of sex-sorted ram spermatozoa, but pre-sort addition of CLCs reduced (P < 0.05) sperm quality after post-thaw incubation for 0 h (motility), 3 h (motility, average path velocity, viability and acrosome integrity) and 6 h (motility, average path and curvilinear velocity, straightness, linearity, viability and acrosome integrity). Seminal plasma had a differential effect (P < 0.001) on sex-sorted and non-sorted spermatozoa. Post-thaw supplementation of increasing levels of seminal plasma caused all motility characteristics of sex-sorted, frozen-thawed spermatozoa to decline (P < 0.05); conversely, non-sorted, frozen-thawed spermatozoa exhibited improvements (P < 0.05) in motility, viability, acrosome integrity and mitochondrial respiration. In summary, incorporation of catalase, CLCs and seminal plasma into the sorting protocol failed to improve post-thaw sperm quality and, consequently efficiency of sex-sorting of ram spermatozoa. The paradoxical effect of seminal plasma supplementation on the in vitro characteristics of ram spermatozoa provides further evidence that sex-sorting by flow cytometry produces a selected population of cells with different functions compared with non-sorted spermatozoa.