Sensitivity of domestic cat (Felis catus) sperm from normospermic versus teratospermic donors to cold-induced acrosomal damage

Freeze-thawing cat sperm in cryoprotectant results in extensive membrane da mage. To determine whether cooling alone influences sperm structure and via bility, we compared the effect of cooling rate on sperm from normospermic ( N; > 60% normal sperm per ejaculate) and teratospermic (T; < 40% normal spe rm per ejaculate) domestic cats. Electroejaculates were divided into raw or washed (Ham's F-10 + 5% fetal calf serum) aliquots, with the latter resusp ended in Ham's F-10 medium or Platz Diluent Variant Filtered without glycer ol (20% egg yolk, 11% lactose). Aliquots were 1) maintained at 25 degrees C (no cooling; control), 2) cooled to 5 degrees C in a commercial refrigerat or for 30 min (rapid cooling; similar to 4 degrees C/min), 3) placed in an ice slush at 0 degrees C for 10 min (ultrarapid cooling; similar to 14 degr ees C/min), or 4) cooled to 0 degrees C at 0.5 degrees C/min in a programma ble alcohol bath (slow cooling); and aliquots were removed every 4 degrees C. All samples then were warmed to 25 degrees C and evaluated for percentag e sperm motility and the proportion of intact acrosomes using a fluorescein -conjugated peanut agglutinin stain. In both cat populations, sperm percent age motility remained unaffected (p > 0.05) immediately after exposure to l ow temperatures and after warming to 25 degrees C. However, the proportion of spermatozoa with intact acrosomes declined (p < 0.05) after rapid coolin g (similar to 4 degrees C/min) to 5 degrees C (N, 65.6%; T, 27.5%) or ultra rapid cooling (similar to 14 degrees C/min) to 0 degrees C (N, 62.1%; T, 23 .0%) in comparison to the control value (N, 81.5%; T, 77.5%). Transmission electron microscopy of cooled sperm revealed extensive damage to acrosomal membranes. In contrast, slow cooling (0.5 degrees C/min) to 5 degrees C mai ntained (p > 0.05) a high proportion of spermatozoa with intact acrosomes ( N, 75.5%; T, 68.3%), which also remained similar (p > 0.05) between cat pop ulations (N, 64.7%; T, 56.8%) through continued cooling to 0 degrees C. Res ults demonstrate that 1) rapid cooling of domestic cat sperm induces signif icant acrosomal damage without altering sperm motility, 2) spermatozoa from teratospermic males are more susceptible to cold-induced acrosomal damage than normospermic counterparts, and 3) reducing the rate of initial cooling markedly decreases sperm structural damage.