Antibiotics for bull semen frozen in milk and egg yolk extenders

In six experiments, gentamicin, clindamycin, amikacin, minocin, tylosin, and Linco-Spectin were tested for their effect on motility and fertility of frozen bull spermatozoa and all but clindamycin were used in fertility trials. Antibiotics were added to raw (unextended) semen and nonglycerol portions of the three commonly used semen extenders, whole milk, egg yolk-Tris, and egg yolk-citrate. Semen was frozen in .5-ml straws, stored in liquid nitrogen, and thawed at 37 degrees C for 30 s. Postthaw percentage of motile spermatozoa in antibiotic-treated semen was different for individual bulls in each experiment. Percentage of motile sperm was slightly but significantly depressed at the higher concentrations of clindamycin and Linco-Spectin tested in whole milk and with minocin in the two egg yolk extenders. In general, nonspermicidal concentrations of each antibiotic were established. Of five antibiotics tested for fertility, only gentamicin reduced fertility on the basis of 59-d nonreturn rates.