Evaluation of a Yeast Single Cell Protein with Young Pigs

Abstract

The digestibility and utilization of nitrogen (N) were compared between a yeast single-cell protein (SCP) and dehulled soybean meal (SBM) during two, 5-day total collection periods. Semipurified diets supplying 18% crude protein from either SCP or SBM as the only protein sources were fed in a metabolism trial to 12 pigs that weighed 5.6 kg at the beginning of the experiment. Both diets were supplemented with methionine. These same pigs were used in an intermediate period to obtain estimates of metabolic fecal nitrogen (MFN) and endogenous urinary nitrogen (EUN) of .101 and .313 g/lOOg of feed intake, respectively. These estimates were made by extrapolating nitrogen intake to zero from low protein (3, 6, 9 and 12%), dried skim milk diets. Apparent dry matter and N digestibility coefficients were higher (P<.01) for the SCP than for the SBM diet. The differences between diets were greater in period 1 than in period 2 (interactions, P<.01 for DM and P<.05 for N). Apparent biological values (BV) of 72.5 and 73.7 for SBM and SCP, respectively, were not significantly different (P>.10). Apparent net protein utilization (NPU) values of 64.8 and 69.3 for SBM and SCP diets, respectively, differed (P<.10) and the source difference was greater in period 1 than in period 2 (interaction, P<.10). True BVs of 84.4% and 84.1% were similar, as were true NPU values of 78.1 and 81.6% for SBM and SCP diets, respectively. Plasma urea N levels, but not plasma α-amino N, were higher (P<.05) 4 hr after feeding in pigs fed SBM than in those fed SCP. In a second experiment the yeast SCP product replaced none, one-third, two-thirds or all of the SBM in the diet of weanling pigs. Diets were not supplemented with methionine. The SCP levels did not affect (P>.05) average daily gain (ADG), average daily feed intake (ADF) and gain to feed ratio (G:F). As SCP level increased, the plasma urea N (PUN) level decreased (linear and quadratic effects, P<.01). Diets did not affect plasma α-amino N concentration. In a third experiment, the SCP product, at a level that replaced 50% of the SBM in the diet, was compared with a second SCP product at the same feeding level and with a control diet containing no SCP. Diets were not supplemented with methionine. Source of protein did not (P>.05) differentially affect ADG, ADF, G:F, PUN and plasma a-amino N of weanling pigs. Results of these experiments indicate that the SCP product described and tested is an excellent protein feedstuff for use in diets fed to weanling pigs.