Estimation of sperm concentration limits to produce intrauterine insemination doses in swine.

This study evaluated the effect of sperm concentration of boar semen doses, for intrauterine artificial insemination (IUAI), on semen quality and established concentration limits for their production. Twenty ejaculates from four crossbred mature PIC® boars were collected to produce 50 mL semen doses in a split sample, reaching the following sperm concentrations: ~20, 30, 60, and 100 × 106  cells/mL. Doses were produced using Androstar® Plus, stored at 17°C, and evaluated until 120 h of storage. There was a linear decrease in sperm motility as the sperm concentration increased (p linear < .01). The concentration which no longer affected the total and progressive motility was 59 and 55 × 106 cells/mL, respectively (corresponding to 71% and 62%, respectively). The pH linearly decreased as the sperm concentration increased (p < .01); yet, at 72 and 120 h, the parameter dramatically reduced in boar semen doses with 60 and 100 × 106  cells/mL. The percentage of cells with intact plasma and acrosomal membranes or with high mitochondrial membrane potential was not influenced by the sperm concentration (p ≥ .15). In conclusion, sperm motility was negatively affected in highly (60 and 100 × 106  cells/mL) concentrated doses. To achieve suitable sperm motility, boar semen doses may not surpass the sperm concentration of 55 × 106  cells/mL. The effect of low-concentrated boar semen doses on sperm quality still needs to be better evaluated, mainly considering the influence of extender type and thermo-resistance conditions.