Effect of Chlortetracycline, Sulfamethazine and Procaine Penicillin on the Performance of Starting Pigs

C HLORTETRACYCLINE is well established as an additive used extensively in swine rations to aid in the prevention of losses from enteritis (Braude et al., 1953; Jukes, 1955), cervical abscesses (Gouge et al., 1957, 1958), atrophic rhinitis (Gouge et al., 1956; Elliott, 1957), and for increasing body weight gains and improving feed efficiency (Beeson and Conrad, 1955; Catron, 1961; Elliott et al., 1958; Smith et al., 1956; Teague, 1962). Combinations of other antibiotics with chlortetracycline have been fed, but none has been thoroughly investigated. Sulfamethazine, active against both Grampositive and Gram-negative bacteria, has been used for disease therapy, but has not been used in feeds on a continuous basis for preventing diseases or improving production, although limited research has shown efficacy against diseases when feed was used as the route of administration. Burkhart et al. (1948) found that high concentrations of sulfamethazine occurred in the blood within one hour after administering the drug in the feed. Thorp and Straley (1946) obtained clinical improvements in swine with necrotic enteritis and pneumonia caused by Hemophilus suis when sulfamethazine was given in the feed. Larsen (1948) successfully treated dysentery in swine. These reports established the therapeutic efficacy of sulfamethazine at concentrations ranging from 65 to 98 rag. per pound of body weight per day in their feed. To determine the effects of combinations of chlortetracycline, sulfamethazine and procaine penicillin in pig starter rations on growth rate, feed efficiency, and disease prevention and the safety of the combination, the following experiments were condUcted under laboratory and farm conditions.