The antimicrobial compound U-82,127 (Pharmacia & Upjohn, Kalamazoo, MI) is a thiopeptide that belongs to a series of cyclic peptide antibiotics produced by Streptomyces arginensis. It is active mainly against Gram-positive organisms. A study involving 576 growing-finishing pigs was conducted at six locations to assess the efficacy of the growth-promoting compound from approximately 19 to 89 kg BW. The basal diet was an unmedicated corn-soybean meal diet fortified with vitamins and trace minerals and containing 16% CP (.80% lysine) during the growing stage (to 54 kg) followed by 13% CP (.60% lysine) during the finishing stage. Dietary dose concentrations of the antimicrobial compound were 0, 3.3, 6.6, and 9.9 mg/kg. At each location, there were six replications of four pigs (two barrows and two gilts) per pen. Diets and water were available for ad libitum consumption. The antimicrobial was provided in coded bags, and investigators were blind to the treatments. The ADG during the growing stage was improved by all levels of the antimicrobial (P < .04), but only the 6.6 mg/kg level improved ADG during the finishing stage (P < .03). Feed:gain was improved by all concentrations of the antibiotic (P < .01) during the growing stage and by the two lower levels of the drug (P < .06) during the finishing stage. Over the entire study, the antimicrobial compound improved ADG (linear, P < .06) and feed:gain (quadratic, P < .01; minimum feed:gain was at 6.2 mg/kg). The lowest dose with a 90% confidence interval of its predicted value not overlapping with the predicted value of the control was 2.3 mg/kg; thus, the efficacious dose range for improving feed/gain was between 2.3 and 6.2 mg/ kg. Neither death loss nor pig removal from the experiment was affected by treatment. The results indicate that the antimicrobial compound U-82,127 is an effective growth-promoting agent for growing-finishing pigs.

Two experiments were conducted to evaluate the response of broiler chickens to addition of bacitracin methylene disalicylate (BMD) to diets containing salinomycin. In each experiment, five tests were conducted at different locations. In Experiment 1, all diets contained 66 mg salinomycin/kg of diet for the first 42 days and either 0 or 33 mg BMD/kg of diet for the entire 49-day feeding period. In Experiment 2, all diets contained 66 mg salinomycin and 50 mg roxarsone/kg of diet for the first 42 days and either 0, 11, 33, or 55 mg BMD/kg of diet for the entire 49-day feeding period. In Experiment 1, addition of 33 mg BMD/kg of diet significantly (P less than .05) improved body weights and feed utilization. Results were similar in all five tests. In Experiment 2, addition of 11, 33, or 55 mg BMD/kg of diet significantly (P less than .05) increased body weights. In one location the addition of 55 mg BMD/kg of diet resulted in no significant difference in body weight compared with those fed the unsupplemented diet, but in all other locations the response was similar. Addition of 33 or 55 mg BMD/kg of diet resulted in improved (P less than .05) feed utilization when all tests were combined. Feed utilization was not improved in all locations by the addition of BMD.

Six trials were conducted at various locations to determine the response of broiler chickens to combinations of zinc bacitracin and roxarsone when fed in the presence of narasin. The addition of zinc bacitracin at 55 mg per kg significantly improved growth rate and feed utilization when data from all locations were combined. There was no effect of roxarsone fed at 50 mg per kg on BW or feed utilization, nor was there an interaction of roxarsone and zinc bacitracin on BW. There was a significant interaction of roxarsone and zinc bacitracin for feed utilization; addition of zinc bacitracin significantly improved feed utilization both in the presence and absence of roxarsone, but the improvement was greater in the absence of roxarsone.

Five trials were conducted at various locations to determine the response of broiler chickens to the addition of zinc bacitracin to diets containing both salinomycin and roxarsone. Results indicate that when a combination of salinomycin and roxarsone is used as an anticoccidial, the addition of zinc bacitracin at 33 or 55 mg/kg diet will improve growth rate and feed utilization by broiler chickens. Regression of body weight and feed utilization on dietary levels of zinc bacitracin indicated that each milligram of zinc bacitracin in the diet increased the 49-day weight of broiler chickens by .92 g and reduced the feed required per gram of gain by .0012 g.

Studies were conducted at six locations over a 7-yr period to evaluate the response of broiler chickens to bacitracin methylene disalicylate (BMD) and roxarsone in the presence of diets containing 3 ppm halofuginone/kg feed. Treatments consisted of a 2 x 2 factorial arrangement with 0 or 55 mg BMD and 0 or 50 mg roxarsone/kg feed. These additives were fed beginning with day-old chicks and were removed 6 days before termination of the study, which varied in length from 48 to 56 days among locations. Body weights were significantly improved (P less than .05) by the addition of either BMD or roxarsone with a significant interaction (P less than .05) between BMD and roxarsone. Roxarsone improved body weights only in the presence of BMD. Feed utilization was significantly (P less than .05) improved by addition of either BMD or roxarsone, with no interaction between the two products.