Sperm parameters after cushion centrifugation of stallion cooled-stored semen

Clinical practice suggests that some stallions may benefit from semen centrifugation and reextension after cooled storage and shipping. This study aimed to determine the effects of centrifugation and resuspension on stallion cooled semen. It was hypothesized that an egg-yolk based extender would improve sperm motilities parameters after cushion centrifugation (CC) of cooled-stored semen. Ejaculates (n = 25) from 5 mature stallions were extended to 25 million/ml with a skim milk-based extender (CST, Animal Reproduction Systems, Chino, CA) and stored for 24 or 48 hours in a passive cooling device (Equine-Express II; EE, Exodus Breeder, York, PA) or Equitainer (EQ; Hamilton BioVet, Ipswich, MA). After storage, semen was processed through CC (1000 × g, 20 minutes), supernatant was discarded, and pellet resuspended in 2 ml of INRA 96 (IMV, Maple Grove, MN) or Botucrio (Botupharma, Phoenix, AZ). Noncentrifuged aliquots of cooled stored semen served as controls. Motility parameters were assessed with a computer-assisted sperm analyzer (Spermvision, MOFA, Verona, WI) before and after CC and in control samples that were not processed. Assessment included total motility (TM) and progressive motility (PM). Data were analyzed using a mixed model (R project) accounting for fixed (containers, time, and extenders) and random (stallion and ejaculate) effects. CC did not affect (p > 0.05), TM at 24 or 48 hours, whereas PM tended (p = 0.07) to decrease after centrifugation and 24 hours of storage (Table). Additionally, after 24 hours, none of the other sperm kinetics parameters were affected (p > 0.05) by the type of extender, processing with CC or the type of container. These results could either suggest that: 1) CC cannot be used to enhance sperm kinetics parameters of cooled-stored semen; 2) or it could be possible that apparent benefits of CC cannot be seen on normospermic stallions (as used herein). Thus, it is reasonable to speculate that if stallions with poor semen cooling quality were used, results may be different. In addition, CC has another benefit that was not assessed here; upon arrival, semen needs to be concentrated in a small volume for deep uterine horn insemination. Additional studies are warranted to assess effects of CC on sperm motility parameters on stallions with poor-quality semen cooled semen.

Keywords: Sperm motility, semen quality, horse, equine, andrology

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.