Evaluation of conjugated linoleic acid and dietary antibiotics as growth promotants in weanling pigs

An experiment was conducted to determine the efficacy of dietary conjugated linoleic acid (CLA) as a growth promotant in weanling swine. Weanling pigs (n = 192; 7.6 kg and 29 d of age) were randomly assigned to four treatment s that were arranged as a 2 x 2 factorial. Concentrations of dietary CLA (0 or 0.6%) and antibiotics (+/-) constituted the main effect variables. Diet ary CLA treatments consisted of a 1% addition of an oil containing 60% CLA isomers or 1% soybean oil, and dietary antibiotic treatments were antibioti cs or no antibiotics. The experimental diets were fed for 9 wk in four phas es (1, wk 1; 2, wk 2 and 3; 3, wk 4 through 6; and 4, wk 7 through 9), afte r which all pigs were fed identical medicated diets for the duration of the finishing phase. Live weights were recorded at wk 17 postweaning and at ma rketing to determine any residual effects of dietary treatments on finisher ADG and days to market. Medicated diets fed during phases 1 and 2 containe d 55 mg carbadox/kg; during phase 3 contained 299 mg tilmicosin/kg; and dur ing phase 4 contained 110 mg tylosin and 110 mg sulfamethazine/kg. Pigs fed medicated diets had higher overall ADG than pigs fed unmedicated diets for wk 0 through 9 (P < 0.03). Gain:feed (G:F) was greater for pigs fed medica ted diets than for pigs fed unmedicated diets during phase 1 (P < 0.03) and for the duration of the nursery phase (P < 0.03). There were no effects of CLA on ADG, ADFI, or G:F. There were no residual effects of nursery CLA or antibiotics on finisher ADG and days to market. Blood samples collected fr om a subset of pigs (n = 72) at the completion of phases 2, 3, and 4 were a ssayed for serum IGF-I and antibody concentrations to porcine reproductive and respiratory syndrome virus (PRRS-V) and Mycoplasma hyopneumoniae. There was a tendency for pigs fed medicated diets to have greater IGF-I concentr ations than pigs fed unmedicated diets at the completion of phase 4 (P < 0. 06). Pigs fed CLA had greater antibody titers (P < 0.02) to Mycoplasma hyop neumoniae at d 63 than pigs fed diets without CLA. These results indicate t hat feeding 0.6% dietary CLA did not enhance growth performance in weanling swine and that the use of dietary antibiotics can increase production effi ciency in nursery pigs. Furthermore, there were no interactions between CLA and dietary antibiotics on the variables addressed in this study.