Comparison of three markers for the determination of bacterial protein in terminal ileal digesta in the growing pig

Abstract

The aim of the study was to compare three methods commonly used to determine the concentrations of bacterial protein in digesta collected from the terminal ileum of growing pigs that had been fed a casein-based diet. The amounts of bacterial protein in terminal ileal digesta were determined using three different markers: 2.6-diaminopimelic acid (DAPA) and the d-amino acids, d-aspartic acid (d-Asp) and d-glutamic acid (d-Glu). The effectiveness of each marker was compared against a control based on physical fractionation by centrifugation. The total bacterial protein concentrations derived from the markers d-Asp and d-Glu were significantly different (p = 0.05) to those calculated from DAPA and the control, but there was no difference between DAPA and the control. The percentage of bacterial nitrogen ranged from 40% to 52% dependent on the marker used. Bacterial protein expressed as a percentage of the total protein, ranged from 48% to 62%, a substantial proportion of which (12-28%) was derived from lysed bacterial cells. Statistical correlations between the estimation methods were low. Such poor correlation between the markers may be the result of random errors such as variance in the epimerization of the two d-amino acids during protein hydrolysis. DAPA was accepted as a reliable marker for determining microbial protein in ileal digesta.

2,6-Diaminopimelic acid as a biological marker of rumen synthesis and fermentation capacities in the transition period and early lactation of dairy cows

“…Gram-positive bacteria contain approximately 30-60% peptidoglycan, whereas gram-negative bacteria have only 10% peptidoglycan (Schoenhusen et al 2008). Amino acid composition and structure of peptidoglycans in gram-positive bacteria varies greatly, whereas that of gram-negative bacteria is more consistent (Miner-Williams et al 2013). Knowledge of the DAPA concentration in the walls of bacterial cells is the basis for verification of the hypothesis of the possibility of applying DAPA in the rumen content as a marker of the synthesis of bacterial biomass.…”