Abstract
A total of 360 weanling pigs (241 × 600, DNA; initially 5.4 ± 0.01 kg) were used in a 45-d study to evaluate the effects of a yeast extract on growth performance, fecal dry matter, stress-relevant blood antioxidant criteria, and cytokine production. Pens of pigs were randomly allotted to 1 of 6 dietary treatments in a generalized randomized block design with 5 pigs per pen and 12 pens per treatment. Pigs were blocked such that there were 4 replications each of light, medium, and heavy weight pens per treatment. Diets were corn-soybean meal-based and consisted of a negative control diet, a positive control diet which was the negative control diet + 55 mg/kg carbadox (Mecadox 2.5, Phibro; Teaneck, NJ),the positive control diet with 0.04% yeast extract (Ceretide S, Planet Bioscience; Boon Lay Way, Singapore), and the negative control diet with either 0.04, 0.08, or 0.12% yeast extract. Treatment diets were fed in three phases from d 0 to 10 (phase 1), d 10 to 24 (phase 2), and d 24 to 45 (phase 3). On d 10 and 24, fecal samples were collected from the same 3 randomly selected pigs in each pen to determine fecal dry matter (DM) and fecal scores. Blood samples were collected on d 10 and 45 from the same representative pig in each pen for total antioxidant capacity (TAC), superoxide dismutase (SOD), and cytokine panel. Overall (d 0 to 45), final BW increased (P < 0.05) while ADG and ADFI tended to increase (P < 0.10) for pigs fed diets containing carbadox compared to pigs fed diets without carbadox with either none or 0.04% added yeast extract. Gain:feed ratio increased (P = 0.017) when 0.04% yeast extract was added to the positive and negative control diets. For fecal DM on d 10, increasing yeast extract in diets without carbadox increased fecal DM (linear, P = 0.005). Additionally, pigs fed carbadox had increased (P < 0.05) fecal DM on d 10 and 24 compared to pigs not fed carbadox. There were no significant treatment differences observed on d 10 for TAC; however, TAC decreased (linear, P = 0.008) on d 45 as added yeast extract increased. Increasing yeast extract tended to decrease (linear, P = 0.095) serum SOD activity on d 10 while no significant treatment differences were observed on d 45. In summary, pigs fed carbadox with or without 0.04% yeast extract had increased overall ADG and fecal DM. Additionally, feeding 0.04% yeast extract led to an improvement in overall G:F and increasing yeast extract improved d 10 fecal DM.