The Effectiveness of Adding Penicillin to a Mixture of Chlortetracycline and Sulfamethazine to Improve Growth of Weanling Pigs

Three groups, each of five pigs, of initial age 5–6 weeks and initial weight 12 kg, were placed on each of three wheat-soybean-meal-based diets of 18% crude protein content. The diets contained either (a) no antibiotic, (b) 110 mg/kg chlortetracycline hydrochloride, 110 mg/kg sulfamethazine and 55 mg/kg penicillin, or (c) diet (b) minus penicillin. Both antibiotic treatments produced a similar growth response of approximately 12%, which resulted partly from an increased feed intake and partly from an improved efficiency of feed utilization.