Postthaw survival and fertility of frozen bull spermatozoa treated with antibiotics and detergent.

Five factorial experiments were conducted, each with 10 bulls, three extenders, and six antibiotic treatments to determine safe levels of new antibiotics to add to bull spermatozoa. Dicloxacillin, cephapirin, ceforanide, gentamicin, and minocin were added at five concentrations to whole milk, egg yolk-Tris, and egg yolk-Tris detergent (sodium triethanolamine lauryl sulfate) extenders with penicillin and streptomycin as a control. Semen was extended to 20 X 10(6) sperm/ml, packaged in .5-ml straws, frozen and stored in liquid nitrogen, and thawed at 35 degrees C for 30 s. Two people assessed postthaw percentage of motile spermatozoa from two straws per treatment. Bulls and extenders always affected sperm motility significantly. Percentage of intact acrosomes of spermatozoa was assessed in selected treatments but did not differ in any experiment. Sodium triethanolamine lauryl sulfate tended to improve cryopreservation of spermatozoa. Percentage of motile spermatozoa in milk declined when concentrations of dicloxacillin exceeded 200 micrograms/ml or when gentamicin, as Gentocin, exceeded 500 micrograms/ml. Minocin was toxic at all levels tested in egg yolk and was nontoxic to sperm in milk extender at concentrations less than or equal to 100 micrograms/ml. Cephapirin and ceforanide were innocuous at all concentrations tested (200 to 2000 micrograms/ml). Fertility with cephapirin (500 micrograms/ml) added to an extender containing control antibiotics resulted in a 56-d nonreturn rate of 75.5 versus 72.1% for the control.