Abstract
Extended semen from six Hereford bulls was placed in .25-ml Continental straws and frozen in the vertical position. Treatments were arranged factorially with glycerol levels of 5, 7, 9 or 11%; semen cooled from 5 to −130 C in 3.5 (fast), 20 (moderate) or 40 min (slow); and thawed in water at 5 C for 3 min, 35 C for 12 sec, 55 C for 8 sec, 75 C for 7 sec or 90 C for 5 seconds. Fast freezing resulted in greater post-thaw motility than moderate (P < .05) or slow rates (P < .01), regardless of thawing method. Glycerol levels of 7 to 11% provided optimal survival when averaged over rates of freezing and thawing (P < .05). Post-thaw motility improved as the temperature of the thawing bath was increased from 5 to 55 C (P < .01). Further increases in thawing bath temperature to 90 C did not enhance survival. The post-thaw motility of spermatozoa frozen rapidly in straws and thawed at 55 to 90 C exceeded that for ampules from split-ejaculates frozen in 1.O-ml ampules (P < .01). Semen from one Angus, two Hereford and three Charolais bulls was frozen in a second study at the fast, moderate and slow rates in straws maintained in the horizontal or vertical position. The final extended semen contained 5, 7, 9 or 11% glycerol; and all semen was thawed in 75 C water for 7 seconds. Fast freezing resulted in post-thaw motility equal to or greater than that with the slower methods when the spermatozoa were suspended in 5 to 9% glycerol, but the slower rates of freezing were superior when 11% glycerol was used (P <.01). Glycerol levels of 7 and 9% were superior to 11% (P < .05), when averaged over all other factors. Higher post-thaw motility was obtained when spermatozoa were frozen in straws placed horizontally as opposed to vertically (P<.01). Copyright © 1975. American Society of Animal Science. Copyright 1975 by American Society of Animal Science.