The Effect of Streptomycin upon the Livability and Bacterial Content of Bovine Semen

Abstract

Since penicillin-resistant organisms are encountered in bovine semen, it seemed desirable to study the value of streptomycin as an antibacterial agent. Streptomycin was added to 10 samples of bull semen diluted 1:24 with egg yolk-citrate diluter at the rate of 0, 100, 250, 500, 750, 1,000, 1,250, 1,500 and 2,000 units or [gamma] per ml. of diluted semen. Levels of streptomycin ranging from 100 to 1,000 [gamma] per ml. did not significantly affect the ability of the spermatozoa to maintain motility during 20 days'' storage at 4.5 C. Levels of 1,250, 1,500 and 2,000 [gamma] per ml. of diluted semen brought about a significant decrease in spermatozoan livability. Based on linear regression, the mean % of motile spermatozoa during 20 days'' storage decreased by 0.5% for each addition of 250 [gamma] of streptomycin. Bacterial plate counts on 9 semen samples demonstrated that streptomycin inhibited bacterial growth in diluted semen as compared with untreated controls. Levels above 100 [gamma] per ml. were especially effective; the greatest antibacterial activity was obtained in freshly diluted semen and diluted semen stored for 8 days. Initial plate counts for 10 ejaculates of freshly collected bull semen ranged from 2,000 to 350,000 bacteria per ml. of undiluted semen, with a mean of 73,000 bacteria per ml. Streptomycin assays by the standard cylinder plate method, using Bacillus subtilis as the test organism, showed no significant loss in streptomycin activity in diluted semen stored for 8 and 16 days at 4.5 C.