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

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Abstract
Since neither penicillin nor streptomycin alone will completely control bacteria in diluted bull semen at levels which are not injurious to the spermatozoa, a combination of the antibiotics was investigated. Eight combinations of the Na salt of penicillin and streptomycin sulfate ranging from 100 to 1000 units of each per ml. of diluted semen were studied using 13 semen samples. Analysis of variance involving 1170 motility estimations showed that none of the combinations caused a significant effect upon the ability of the spermatozoa to remain motile during a 20-day storage period. Bacterial plate counts on 5 semen samples showed that penicillin and streptomycin together effectively controlled bacterial growth at all levels tested. Since the initial amount of bacterial contamination in these samples was very low, the next 5 samples were inoculated with broth cultures of bacteria isolated from previous semen platings. After 8 days of storage at 5[degree]C there were marked decreases in the bacterial plate counts as compared with the same samples plated before storage. Negative plate counts consistently were obtained at all levels above 100 U. each of penicillin and streptomycin per ml. of diluted semen.

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