Influence of Extender, Extension Rate, and Glycerolating Technique on Fertility of Frozen Bull Semen

Abstract

In four field trials involving 57,791 inseminations with ampuled frozen semen, there was no difference in motility or fertility when glycerol was included initially in Tris-fructose-glycerol-yolk extender or when it was added slowly after cooling to 5 C. Fertility in citrate-glycerol-yolk extender also was the same when glycerol was added slowly in four steps or in one step at 5 C. Thus, slow addition of glycerol is not necessary. Reduction in pH of the citrate extender from 7.0 to 6.5 did not affect fertility. The 60- to 90-day per cent nonreturns for Tris extender at pH 6.5 and 6.75 were 74.1 and 71.9 (P = 0.10). Sperm motility following freezing and thawing in Tris extender was slightly superior to that in citrate extender, but there was no difference in fertility. Fertility was 0.5 and 1.5 percentage units lower in two trials when 12 × 106 motile sperm numbers per ampule before freezing were compared with 24 × 108 motile sperm (P > 0.10). After freezing and thawing, motile sperm numbers per ampule ranged from 3 × 106 to 23 × 106. Correlations between these sperm numbers and fertility in three experiments were 0.17, 0.26, and 0.42. Thus, sperm numbers in the range studied accounted for only 3 to 18% of the variation in nonreturn rate. Increasing sperm numbers had little effect on improving fertility of low-fertility bulls. © 1970, American Dairy Science Association. All rights reserved.