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Effect of Rates of Freezing, Thawing and Level of Glycerol on the Survival of Bovine Spermatozoa in Straws¹

Colorado State University, Fort Collins 80523

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).

¹ Animal Reproduction Laboratory, Department of Physiology and Biophysics. The advice and suggestions of Mr. George Covington, Cryenco, Denver, CO 80216, for the design of the freezing apparatus used in this study are greatly appreciated. Supported in part by grants-in-aid from Cryenco and Noba, Inc. through the National Association of Animal Breeders.

² Present address: Institute Nacional de Investigaciones Pecuarias, Km. 15 1/2 Carretera Mexico-Toluca, Palo Alto, D. F., Mexico.

³ Continental Plastics, Inc., P. 0. Box 336, Darien, WI 53114.

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