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Effect of Sperm Numbers on Fertility of Frozen Bull Spermatozoa in Skim Milk Diluent¹

Dairy Breeding Research Center, Department of Dairy Science, The Pennsylvania State University, University Park 16802

ABSTRACT

Insemination doses of 10, 15, and 20 million progressively motile spermatozoa prior to freezing were compared in a split-ejaculate fertility experiment involving 4,603 first service inseminations to 34 semen samples from six Angus bulls. Based on 60- to 90-day nonreturn rates, fertility was significantly lower for inseminating doses of 10 and 15 X 10⁶ than 20 X 10⁶ motile sperm (61, 62, and 70%). The 1-ml doses of skim milk diluted semen were frozen in glass ampules. The post-thaw number of motile sperm per ampule after freezing and storage for 3 wk in liquid nitrogen averaged 5.5, 8.4, and 12.4 X 10⁶ for corresponding pre-freeze numbers of 10, 15, and 20 X 10⁶ motile sperm/ml and ranged from 4.0 to 15.7 X lC/ml. Frozen semen packaged in ampules should contain more than 8.4 X 10⁶ motile cells post-thaw per ampule.

¹ Authorized for publication on April 22, 1974 as Paper No. 4678 in the journal series of The Pennsylvania Agricultural Experment Station.