Comparison of procedures for estimating microbial contamination of feed residues from in situ bags in sheep

Abstract

situ protein degradations of grass hay and molassed sugarbeet pulp were performed in the rumen of sheep. Three methods, namely labelling with 35S, measuring cytosine as an internal microbial marker and dissolving contaminating microbes in neutral detergent solution were compared with the aim of choosing the method that best estimated microbial contamination of in situ feed residues. Corrected protein degradation values were higher (P<0.05) than the values uncorrected for microbial contamination. The cytosine method gave the highest estimates of microbial presence in in situ bag residue followed by labeling with 35S. At incubation times up to 16 h, considerable quantities of dietary cytosine might have been present in the bag residue causing an overestimation of the amount of microbes present in the residue. In contrast, the neutral detergent procedure underestimated N disappearance because it removed
97.5% of the N content of solid associated microbes. Due to weaknesses of the cytosine and neutral detergent methods, the 35S technique was considered to be the best method for correcting microbial contamination of residues in the bags during in situ determination of feed degradability in the rumen.