Effect of carbadox and various dietary copper levels for weanling swine.

Two experiments were conducted to evaluate the responses to carbadox and Cu additions in the postweaning diet of swine. The first trial contained 470 pigs in five replicates in a 2 X 5 factorial arrangement in a randomized complete block design. Weanling pigs 4-wk of age were fed diets containing 0 or 55 ppm carbadox and 0, 125, 375 or 500 ppm Cu for a 5-wk period. Copper levels of 125 and 250 ppm resulted in improved pig gains and feed intakes, but at 500 ppm, gains and feed intake declined. Carbadox resulted in enhanced gain and feed performance throughout the trial, but most notably during the initial 2-wk period. Copper improved performance measurements only during the latter 3-wk and for the overall period. There was an additive performance response when carbadox and Cu (125 ppm) were provided in combination. When carbadox was not provided, growth responses increased to the 250 ppm dietary Cu level. Liver, kidney cortex, heart and plasma Cu concentrations increased quadratically as dietary Cu levels increased, with the greatest change occurring between 250 and 500 ppm dietary Cu levels. A N and Cu balance trial in group feeding conditions involving 65 pigs was conducted in two replicates of a 2 X 2 X 5 factorial arrangement of a split-block design. Pigs were ad libitum fed diets with or without 250 ppm Cu and carbadox at 0 or 55 ppm for a 5-wk period. A fifth treatment group fed the 250 ppm Cu plus carbadox diet was pair-fed to the pigs fed the basal treatment. Growth rate and N retention increased when carbadox, but not when Cu was provided. When carbadox and Cu were provided in combination, either ad libitum or pair-fed, N retention was greater than when the basal diet was fed. This response was attributed to the carbadox addition. The carbadox addition reduced Cu retention and liver Cu concentrations.