Fertility of Bull Semen at High Extension Rates in Tris-Buffered Extenders

A 0.20-~ Tris-yolk extender buffered to pH 6.50 or 6.75 was superior to other combinations tested in preserving motility of sperm (P < 0.005). Inclusion of glycerol in the extender added to semen at room temperature was as satisfactory in maintaining sperm motility as glycerolating semen at 5 C. In 3 trials involving 135,579 first inseminations with unfrozen semen, fertility results in a 0.20-~ Tris extender buffered at pH 6.5, and containing 1.0% fructose (w/v) and 6.4% glycerol (v/v) in the final extender, were equal to those obtained with Cornell University Extender. Omission of glycerol resulted in a decrease in 60-to 90-day nonreturns from 73.6 to 71.6% (P < 0.01). The nonreturn rate with semen extended to 8 million motile sperm per milliliter was 73.7 as compared to 72.7% when 4 million motile sperm were used (P > 0.10).