Field Trials with Semen Containing Several Combinations of Antibacterial Agents

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Abstract
In the 1st experiment there were 107 bulls, 1376 collections, and 136,004 services in 6 studs. The basic diluter was yolk-citrate-sulfanilamide. The 60-90 day nonreturn rate was slightly but insignificantly higher with streptomycin than with streptomycin-penicillin. Addition of streptomycin to the basic diluter increased the nonreturn rate by 4.5 percentage units, a highly significant difference. Five hundred units of penicillin and 500 [mu]g of streptomycin gave nonreturn rates slightly and insignificantly higher than 1000 of each. Ninety bulls, 1080 collections, and 118,875 services in 5 studs were used in the 2d experiment Treatments (4) in yolk-citrate diluter were compared: no antibacterial agents, sulfanilamide-streptomycin, streptomycin alone, and penicillin-streptomycin. A greater drop in nonreturn rate from the 1st to the 2d day after collection occurred with penicillin-streptomycin than with the other treatments. In general, the lowest nonreturn rate was with no antibacterial agents and next lowest with penicillin-streptomycin. Best results were with sulfa-streptomycin. With breedings on the 2d and 3rd day after collection, the nonreturn rates for streptomycin were higher than for penicillin-streptomycin. The difference on the 2d day was not significant. The 23 bulls which were significantly benefited by sulfanilamide-streptomycin as compared with no antibacterial agents, had, with the 3 treatments containing antibiotics, nonreturn rates almost identical with the other bulls. Embryonic mortality, indicated by decline in nonreturn rate from 28-35 days to 60-90 days, became greater with increased length of storage of semen, was greater with no antibacterial agents, and lowest with sulfa-streptomycin. There were significant bull x treatment and stud x treatment interactions.