Energy concentration and phosphorus digestibility in yeast products produced from the ethanol industry, and in brewers' yeast, fish meal, and soybean meal fed to growing pigs

Two experiments were conducted to determine the DE, ME, and standardized total tract digestibility (STTD) of P in 2 novel sources of yeast (C-yeast and S-yeast) and in brewers' yeast, fish meal, and soybean meal fed to growing pigs. The 2 new sources of yeast are coproducts from the dry-grind ethanol industry. The concentrations of DM, GE, and P were 94.8%, 5,103 kcal/kg, and 1.07% in C-yeast; 94.4%, 4,926 kcal/kg, and 2.01% in S-yeast; 93.6%, 4,524 kcal/kg, and 1.40% in brewers' yeast; 91.4%, 4,461 kcal/kg, and 3.26% in fish meal; and 87.7%, 4,136 kcal/kg, and 0.70% in soybean meal, respectively. The DE and ME in each of the ingredients were determined using 42 growing barrows (28.9 +/- 2.18 kg BW). A corn-based basal diet and 5 diets containing corn and 24% to 40% of each test ingredient were formulated. The total collection method was used to collect feces and urine, and the difference procedure was used to calculate values for DE and ME in each ingredient. The concentrations of DE in corn, C-yeast, S-yeast, brewers' yeast, fish meal, and soybean meal were 4,004, 4,344, 4,537, 4,290, 4,544, and 4,362 kcal/kg DM (SEM = 57), respectively, and the ME values were 3,879, 3,952, 4,255, 3,771, 4,224, and 4,007 kcal/kg DM (SEM = 76), respectively. The ME in S-yeast and fish meal were greater (P < 0.05) than the ME in corn and brewers' yeast, whereas the ME in C-yeast and soybean meal were not different from those of any of the other ingredients. The STTD of P in the 5 ingredients was determined using 42 barrows (28.3 +/- 7.21 kg BW) that were placed in metabolism cages. Five diets were formulated to contain each test ingredient as the sole source of P, and a P-free diet was used to estimate the basal endogenous loss of P. Feces were collected for 5 d using the marker to marker method after a 5-d adaptation period. The STTD of P in brewers' yeast (85.2%) was greater (P < 0.05) than the STTD of P in all the other ingredients except S-yeast (75.7%). The STTD of P in C-yeast (73.9%) was not different from the STTD of P in S-yeast and fish meal (67.3%) but was greater (P < 0.05) than the STTD of P in soybean meal (56.7%). In conclusion, the 2 novel sources of yeast contain similar or greater concentrations of energy compared with brewers' yeast, corn, fish meal, and soybean meal, and the STTD of P in the 2 yeast products is not different from the STTD of P in fish meal.