Cryopreservation of boar semen in 0.5mL straws at low spermatozoa concentration is better than high concentration to maintain sperm viability

A manutenção da viabilidade do sêmen suíno criopreservado em palhetas de 0,5mL em baixas concentrações espermáticas é melhor do que em altas concentrações

ABSTRACT:

To date, no studies have been performed evaluating the effect of boar spermatozoa concentration in 0.5mL freezing straws, leading us to examine this question. Each sperm-rich fraction of the ejaculate (n=25) was diluted at five different sperm concentrations (100, 200, 300, 600 and 800 x 10⁶ spermatozoa/mL), packaged in 0.5mL straws, and subsequently frozen. After thawing, the sperm from all of treatment groups were analyzed to determine motility characteristics using a sperm class analyzer (SCA-CASA), and their plasma and acrosomal membrane integrity, mitochondrial membrane potential, sperm membrane lipid peroxidation and fluidity were analyzed by flow cytometry. An increase in spermatozoa concentration above 300x10⁶ spermatozoa/mL in a 0.5mL straw impaired (p<0.05) the total and progressive motility, curvilinear velocity, straight-line velocity, linearity and beat cross frequency. However, the plasma and acrosomal membrane integrity, mitochondrial membrane potential, membrane lipid peroxidation and fluidity were not influenced (p>0.05) by high spermatozoa concentrations at freezing. Therefore, to increase spermatozoa survival and total and progressive motility after thawing, boar spermatozoa should be frozen at concentrations up to 300x10⁶ spermatozoa/mL.

INDEX TERMS:
Cryopreservation; boar semen; spermatozoa concentration; sperm viability; cryoinjury; cryocapacitation; swine