الفهرس 
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Abstract
Six mature native bulls were used in the present study. Semen was collected twice weekly from each bull using artificial vagina, only semen samples with at least 70% sperm motility, 700 X 106 sperm/ml and 80% normal sperm were used for processing. Semen preserved at 5ºC for 7 days in Tris, CU-16, diluent 14, skim milk, skim plus 5% egg yolk and sodium citrate. Best results were obtained with Tris, CU-16, diluent 14 and skim milk plus 5% egg yolk. After preservation in liquid nitrogen at –196ºC the best post-thaw sperm parameters were obtained when semen diluted in Tris, CU-16, diluent 14 or egg yolk milk with glycerol added at 5ºC with appropriated percentage, equilibrated for 2 hours, packaged either in 0.25 or 0.5 ml straw with 30-35 million sperm concentration, frozen 6 cm over liquid nitrogen surface and thawed at 40ºC for 30 seconds.