Nucleic acid-extracted torula yeast from the paper industry as a protein feed for ruminants: A comparison with soybean meal.

We compared nucleic acid-extracted torula yeast (NTY) with soybean meal (SBM) to evaluate NTY as a potential protein feed for ruminants in a metabolic trial using four castrated male goats. NTY was replaced isonitrogenously with SBM at a 25% crude protein (CP) level on a dry matter (DM) basis. NTY has 55% CP and 74% total digestive nutrients on DM. Absorbed N was lower on the NTY diet, but since the urinary N excretion was lower on the NTY diet, no significant between-diet difference in retained N was observed. The efficiency of N utilization (retained N/absorbed N) was significantly higher on the NTY diet. The Lys and Met contents (presumed limiting amino acids for dairy cattle) were higher in NTY than SBM, which may be why N utilization efficiency was higher for the NTY diet. Ruminal ammonia-N and blood serum N were lower on the NTY diet, suggesting that NTY has more rumen undegradable protein than SBM. There was no significant between-diet difference in the visceral disorder indicators or antioxidant activities. Our results indicate that NTY is a safe protein feed with a high CP ratio and high-quality amino acid profile for ruminants that is equivalent to SBM.