The effects of Hydroxyethyl starch (HES) on quality of equine sperm following cold storage and cryopreservation

Abstract

This study aimed at examining the effects of different concentrations of hydroxyethyl starch (HES) on quality of equine sperm following cold storage and cryopreservation. In experiment 1, the semen was collected from 6 stallions (3 replicates). The semen was diluted with extender for cold storage containing different concentrations of HES (2.5%, 5%, 10% and 15%). Extender without HES (0% HES) served as a control group. The temperature of extended semen was gradually decreased to 4 ºC. The quality of sperm in terms of progressive motility and viability was evaluated after cold storage for 6, 24 and 48 hours. This study revealed that equine sperm maintained in extender with 2.5% and 5% HES had similar progressive motility to that observed in a control group when examined within 24 hours of cold storage. However, the 2.5% HES significantly improved progressive motility at 48 hours of cold storage when compared with the control (P<0.05). In addition, this concentration of HES also resulted in a significant improvement of sperm viability only if examined within 24 hours (P<0.05). There was no significant different between the control and 2.5% HES at 48 hours of cold storage (P>0.05). Increasing concentrations of HES to 10% and 15% negatively affected to sperm quality during cold storage. In experiment 2, the semen was collected from 6 stallions (3 replicates). The semen was diluted with a freezing extender containing different concentrations of HES (2.5%, 5%, 10% and 15%). Equine sperm frozen without HES served as a control group. Sperm quality in terms of progressive motility, viability, DNA integrity, acrosomal integrity, membrane functionality (hypo-osmotic swelling test, HOS test) and sperm longevity was examined after cryopreservation and thawing at 0 (10 min), 1, 2, 4 and 6 hours post-thaw. This study revealed that HES influenced on freezing ability of equine sperm. This effect was found to be a concentration dependency. Equine sperm frozen with 2.5% HES had significantly higher progressive motility, viability and acrosomal integrity when compared with a control group (P<0.05). In addition, this concentration of HES also significantly improved progressive motility at 2 and 4 hours post-thaw when compared with the control group (P<0.05). There was no further protective effect of HES against progressive motility if the concentrations of HES were increased over 5%, similarly to the observation in the experiment 1. The 2.5% HES also positively improved sperm viability at 6 hours post-thaw when compared with the control. However, no significant effect was observed at 0 and 4 hours post-thaw. This study concluded that HES supplement in semen extender improved sperm quality during cold storage and cryopreservation. However, optimal concentration of HES was required. The current study indicated that the 2.5% HES was the optimal concentration that yielded the highest efficiency to protect equine sperm during cold storage and cryopreservation. Further study to examine the interactions of HES and other compositions in extender will need to be studied. In addition, it is necessary to use the equine sperm frozen with HES for insemination in order to test their fertilizing ability.