Digestibility of bacterial protein grown on natural gas in mink, pigs, chicken and Atlantic salmon

Abstract

The composition and amino acid digestibility of bacterial protein meal (BPM) produced by Methylococcus capsulatus (Bath), Alcaligenes acidovorans, Bacillus brevis, and Bacillus firmus grown on natural gas were studied. The BPM contained 959 g kg −1 dry matter, 702 g kg −1 crude protein, 103 g kg −1 fat, and 95 g kg −1 nucleic acids. The amino acid composition of BPM was similar to that of fish meal, except for less lysine (6.1 vs. 8.6 g/16 g N) and more tryptophan (2.1 vs. 0.9 g/16 g N). Total tract apparent digestibility (TTAD) in mink, chickens and pigs, and apparent ileal digestibility (AID) in pigs, were obtained by feeding BPM as the sole source of protein. In salmon, TTAD was measured by regression, using diets where BPM substituted fish meal. The average TTAD of total N from BPM was 79.0%, 85.4%, 80.5%, and 81.9% in mink, pigs, chickens and salmon, respectively. Ileal N digestibility in pigs was 78.1%. There were substantial differences among digestibilities of individual amino acids. Arginine and lysine revealed the highest digstibilities and cystine the lowest. The average TTAD coefficients for lysine were 88.7%, 89.2%, 82.6% and 91.7% in mink, pigs, chickens and salmon, respectively, whereas lysine AID in pigs was 84.5%. Average TTAD for cystine was 47.2% in mink, 77.0% in pigs, 44.7% in chickens and 51.9% in salmon. Cystine AID in pigs was 54.9%. Methionine showed TTAD values ranging from 80.9% in chickens to 84.5% in mink, and a pig AID of 83.8%. There were highly significant correlations among the TTAD coefficients of BPM in mink, chicken and salmon, and among the latter figures and AID in pigs ( p<0.001). Although highly significant, the TTAD coefficients in pigs were less correlated to TTAD in mink, chickens and salmon than pig AID ( p<0.001). It appears that small intestine digestion and overall uptake of amino acids from BPM were similar among the investigated species.