Preservation of Bull Semen at Sub-Zero Temperatures

CONTENTS

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EARLY WORK ON FREEZING SEMEN		5

SELECTION OF SEMEN FOR FREEZING		6
	Predicting freezability	6
	Freezability of first and second ejaculates	7
	Freezability of several consecutive ejaculates	7
	Freezability of epididymal sperm	9
	Freezability of washed sperm	10

EXTENDERS FOR FREEZING BULL SEMEN		10
	Proportion of egg yolk in final diluent	10
	Citrate level in final diluent	11
	Storing and freezing diluent	12
	Other diluents	13

DILUTION RATES		14
	Effect of further dilution and refreezing	14

GLYCEROL ADDITIONS		17
	Effect of glycerol on sperm survival at 5° C.	17
	Glycerol levels for freezing semen	18
	Rate, temperature, and method of adding glycerol	18
	Allowing sperm to equilibrate with glycerol	20
	Sugar additions and equilibration time	20
	Substitutes for glycerol	22

FREEZING RATE		22
	Effect of freezing rate on sperm survival	22
	Rate of cooling in plastic and in glass	23

STORAGE TEMPERATURE		24
	Storage at -23° to -79° C.	24
	Use of higher glycerol levels and storage at -20° C.	25