Okapi would benefit from artificial insemination with frozen-thawed sperm in cases where aggression prevents mating or where individuals are geographically disparate. Effective sperm cryopreservation is a prerequisite to this goal. Ejaculates (n = 20) were collected from 7 anesthetized adult male okapi housed individually, or with a female for breeding, throughout the year by electroejaculation, and semen and sperm parameters were assessed. Semen aliquots were centrifuged; resuspended in 500 µL of PBS with the osmolarity adjusted to 35, 75, 150, 600, 1200, and 2400 mOsm; and incubated for 30 min before returning to isosmotic conditions. Semen was extended in TEST containing 1%, 2%, or 4% glycerol with or without 0.5% Equex (Minitube, Verona, WI, USA); 5-µL aliquots were cooled in a Latin square design on a Linkam BCS 196 cryomicrostage (Linkam Scientific, Tadworth, Surrey, UK) at 20�C min–1 to –6� –12�C at which point ice crystal formation was induced (seeded), and cooled further to –70�C before warming at 50�C min–1 to 35�C (okapi body temperature). To investigate cooling effects only, raw ejaculate was cooled to –6�C without seeding and warmed to 35�C. Percent sperm motility and plasma membrane integrity (PMI) were recorded before and after treatments. Differences were examined using one-way repeated measures analysis of variance. No differences in motility, total sperm numbers, or percent normal morphology were observed throughout the year (P > 0.05), although the power of the test was low so that negative findings should be interpreted cautiously. Mean semen volume was 1.3 � 0.19 mL, sperm motility was 29 � 3.2%, with a PMI of 39 � 6.8%; 48 � 2.8% were morphologically normal. High proportions of non-motile, plasma membrane-damaged cells were noted in every ejaculate, and whiplash motility, possibly indicating spontaneous capacitation, was observed in several ejaculates 1 h after collection. Motility was dramatically reduced on either side of isosmotic conditions and was more sensitive to osmotic pressure than was plasma membrane integrity. Cooling of raw ejaculate to sub-zero temperatures without freezing did not result in any loss of motility or PMI, indicating cold tolerence. Superior results were obtained when sperm were frozen-thawed in TEST containing 4% glycerol with 0.5% Equex. Findings indicate that okapi semen collected by electroejaculation routinely contain high numbers of non-motile and plasma membrane-damaged spermatozoa, apparently unrelated to season or the length of time since the male was housed with a breeding female. Okapi spermatozoa are remarkably intolerant of departures from isosmotic conditions, indicating a lack of ability to regulate or withstand volume excursions during osmotic stress events; however, cooling to sub-zero temperatures in the absence of cryoprotectant did not reduce percent sperm motility or PMI, indicating resistance to cold shock. Increasing and maintaining proportions of motile, membrane-intact spermatozoa prior to and during cryopreservation will be critical for development of freezing protocols for this species.
Increased Water Viscosity Enhances Water Intake and Reduces Risk of Calcium Oxalate Stone Formation in Cats
