Effect of Neomycin, Carbadox and Length of Adaptation to Calorimeter on Performance, Fasting Metabolism and Gastrointestinal Tract of Young Pigs1

Five sets of littermate gilts (8.2 ± .19 kg average initial weight) were randomly assigned within litter to a 16% protein corn-soybean meal basal diet (B), B + .308% neomycin, or B + 55 ppm carbadox. Each set was equally-fed individually once daily for 16 d in metabolism cages and 5 d in calorimeters. The average daily feed intake for 21 d was 276 g. Oxygen consumption and CO2production were measured during an 8- to 24-h postprandial period on d 16, 19, 20 and 21, and during a 32- to 48-h postprandial period after the d 21 feeding. Pigs were killed 50 h postprandially for gastrointestinal tract measurements. Dietary supplementation of antimicrobial agents (neomycin and carbadox) resulted in improvements (P<.01) in daily gain and efficiency of feed utilization and lower (P<.05) small intestinal mass in pigs. There was no difference (P>.05) in daily gain, feed efficiency or small intestinal mass between pigs fed neomycin- or carbadox-supplemented diets. Whole-animal fasting O2consumption and CO2production measured during the 8- to 24-h or 32-to 48-h postprandial period were not affected (P>.05) by the supplementation or the source of dietary antimicrobial agents. There were no differences (P>.05) in 8- to 24-h fasting O2and CO2measurements determined on d 16, 19, 20 and 21, indicating that adaptation to calorimeters was not needed by the pigs. The present study, thus, confirms that the growth-promoting effect of certain antimicrobial agents (e.g., carbadox, neomycin) in young pigs may be related to the reduction of the small intestinal mass, and that the hypothetic decrease in maintenance energy demand from reduced small intestinal mass cannot be detected consistently by measuring whole-animal fasting metabolic rate.