Immediate and delayed (after cooling) effects of centrifugation on equine sperm

The objectives of this study were to determine the effects of centrifugation on equine sperm total and progressive motility, viability, and acrosomal integrity. We hypothesized that although high centrifugation forces would be detrimental to equine Equus caballus sperm, recovery rates would increase. Ejaculates from six stallions were collected, extended to a concentration of 25×106 cells/mL, and subjected for 10min to (1) no centrifugation (NC) or (2) centrifugation at 400×g, (3) 900×g, or (4) 4500×g. Before and after centrifugation (Day 0), and after 24h of cooling (Day 1), sperm motility was assessed by computer-assisted semen analysis, and samples were stained with SYBR-14/propidium iodide (PI) for viability and with PI/fluorescein isothiocyanate (FITC)–Peanut aglutinin (PNA) (Arachis hypogaea) for acrosomal integrity. The effect of treatment and day on motility, viability, and acrosomal integrity was determined using a mixed linear model. Compared with the other treatments, centrifugation at 4500×g reduced all end points measured (P<0.05). Both 400×g and 900×g yielded lower recovery rates than that of 4500×g (NC=100.0±0.0%; 400×g=54.4±8.6%; 900×g=75.0±7.1%; 4500×g=97.9±2.8%; P<0.05). Centrifugation at 400×g or 900×g did not damage equine sperm. Based on these findings, further studies of centrifugal forces between 900×g and 4500×g are warranted to determine the optimal force that maximizes recovery rate, minimizes sperm damage, and does not affect fertility.