Effects of transport container and ambient storage temperature on motion characteristics of equine spermatozoa

Abstract

This study was conducted to compare the cooling rates and storage temperatures within equine semen transport containers exposed to different ambient temperatures, and to evaluate the ability of these containers to preserve spermatozoal motility following 24 h of storage under these conditions. In Experiment 1, nonfat dried milk solids, glucose, sucrose, equine semen extender was divided into seven 40-mL aliquots and loaded into seven different semen transport containers: Equitainer I ™, Equitainer II ™, Equitainer III ™, ExpectaFoal ™, Bio-Flite ™, Lane STS ™, and Equine Express ™. After containers were loaded, they were subjected to one of three ambient storage temperatures: 1) 22 °C for 72 h, 2) −20 °C for 6 h followed by 22 °C for 66 h, or 3) 37 °C for 72 h. Cooling rates and storage temperatures of semen extender in each container were monitored with thermocouples and a chart recorder. In Experiment 2, semen from each of three stallions (3 ejaculates per stallion) was diluted to 25 × 10 6 spermatozoa/mL with semen extender, divided into 40 mL aliquots and loaded into transport containers as in Experiment 1. Containers were subjected to one of three ambient storage conditions: 1) 22 °C for 24 h, 2) −20 °C for 6 h, followed by 22 °C for 18 h, or 3) 37 °C for 24 h. After 24 h of storage, spermatozoal motion characteristics (percentage of motile spermatozoa; MOT, percentage of progressively motile spermatozoa; PMOT, and mean curvilinear velocity; VCL) were evaluated using a computerized spermatozoal motion analyzer. Significant interactions were detected among storage conditions and semen transport containers for the majority of the temperature endpoints measured. When exposed to temporary ambient freezing conditions, the lowest temperatures attained by samples in containers ranged from −2.8 to 0.8 °C. Lowest temperature samples attained was not correlated (P > 0.05) with spermatozoal motility under any ambient condition. However, time below 4 °C was highly correlated (P < 0.05) with a reduction in spermatozoal motility. Mean cooling rates from 20 °C to 8 °C did not correlate with spermatozoal motility, except when containers were exposed to temporary freezing conditions. No container cooled samples below 6 °C in 22 °C or 37 °C environments except for the ExpectaFoal ™, in which samples fell below 4 °C under all ambient conditions. Ambient temperature affected MOT, PMOT and VCL of semen stored in all containers (P < 0.05) except for the Equitainer II ™ in which motion characteristics remained high and were similar among all ambient temperatures (P > 0.05). Results suggest that stallion semen may be able to tolerate a wider range of cooling rates and storage temperatures than previously considered safe.