Abstract
Summary In the first experiment there were 107 bulls, 1,376 collections, and 136,004 services in six studs. The basic diluter was yolk-citrate-sulfanilamide. The addition of streptomycin to the basic diluter increased the 60- to 90-day nonreturn rate by 4.5 percentage units, a highly significant difference. The nonreturn rate was slightly but insignificantly higher with streptomycin than with streptomycin-penicillin. Five hundred units of penicillin and 500 γ of streptomycin gave nonreturn rates slightly and insignificantly higher than 1,000 of each. Ninety bulls, 1,080 collections, and 118,875 services in five studs were in the second experiment. Four treatments in yolk-citrate diluter were compared: no antibacterial agents, sulfanilamide-streptomycin, streptomycin alone, and penicillin-streptomycin. A greater drop in nonreturn rate from the first to the second 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. The best results were with sulfa-streptomycin. With breedings on the second and third day after collection, the nonreturn rates for streptomycin were higher than for penicillin-streptomycin. The difference on the second day was not significant, however. The 23 bulls which were significantly benefited by sulfanilamide-streptomycin as compared with no antibacterial agents, had, with the three 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 after service, became greater with increase in length of storage of semen, was greater with no antibacterial agents, and was lowest with sulfa-streptomycin. In the analysis of variance of nonreturn rates for first-day breedings, there were significant bull × treatment and stud × treatment interactions.
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