Effect of torula yeast on growth performance, diarrhea incidence, and blood characteristics in weanling pigs.

Two experiments were conducted to test the hypothesis that torula yeast may replace animal and plant proteins in diets for weanling pigs without negatively impacting growth performance or blood characteristics. In exp. 1, 128 weanling pigs (6.71 ± 0.76 kg) were allotted to four treatments with four pigs per pen and eight replicate pens per diet. Pigs were fed one of four diets from day 1 to 14 post-weaning (phase 1), whereas all pigs were fed a common diet in phase 2 (day 15 to 28). The four dietary treatments included a control diet with 5% fish meal, 2.5% plasma protein, and no torula yeast. The second diet contained 5% fish meal, 4.75% torula yeast, and no plasma protein. The third diet contained 2.5% plasma protein, 6% torula yeast, and no fish meal, and the last diet contained 10.75% torula yeast, no fish meal, and no plasma protein. The inclusion of torula yeast was calculated to replace the amount of digestible Lys provided by fish meal, plasma protein, or both fish meal and plasma protein in the control diet. During the initial 14 d, fecal scores were visually assessed. At the end of phase 1, blood samples were collected and tumor necrosis factor-α (TNF-α), blood urea nitrogen (BUN), peptide YY, immunoglobulin G, total protein, and albumin were analyzed. Results indicated that torula yeast could replace fish meal and plasma protein without affecting growth performance, fecal scores, or blood characteristics of pigs. In exp. 2, 160 weanling pigs (6.11 ± 0.62 kg) were allotted to one of four diets with five pigs per pen and eight replicate pens per diet. Phase 1 diets contained 0%, 10%, 18%, or 26% torula yeast, whereas phase 2 diets contained 0%, 8%, 14%, or 20% torula yeast. Torula yeast was included in diets at the expense of animal proteins and soybean meal. On days 14 and 28, blood samples were collected and concentrations of cytokines, BUN, total protein, and albumin were analyzed. Phase 2 gain-to-feed ratio (G:F) linearly increased (P < 0.01) as the concentration of torula yeast increased in the diets. The concentration of albumin on day 14 linearly increased (P < 0.05) and the concentration of TNF-α was linearly reduced (P < 0.01) as the concentration of torula yeast increased in the diets. In conclusion, under the conditions of this research, torula yeast could replace fish meal and plasma protein without affecting the growth performance of pigs, but inclusion of increasing levels of torula yeast improved G:F of pigs, which may be because of greater nutrient utilization.