Dynamics of microbial contamination of protein during ruminal <i>in situ</i> incubation of feedstuffs

Abstract

The aim of this study was to determine the dynamics of bacterial contamination of feedstuffs during ruminal in situ incubation and to quantify the effects of bacterial contamination on the ruminal in situ degradation of crude protein (CP). Two different approaches using 15 N as a marker were followed, namely: 1. ] and t denotes the incubation time (h). The A max values of most cereals ranged from 32 to 38% of the residue N. For roughages and straw, A max reaches 45 to 100%. A max , but not C, is significantly positively influenced by the NDF content in feedstuffs (P=0.049). The CP content of feedstuffs negatively affects C (P=0.006). The proportion of bacterial CP of total CP within the in situ bag residues was used to correct the apparent CP degradation rate. This correction was numerically lowest for protein concentrates and grains (0 to 3%) and highest for roughages (up to 50%). In conclusion, correction of ruminal protein degradation for bacterial contamination is necessary, especially for roughages. For cereal grains and protein concentrates it seems to be irrelevant.

Comparison of three 15N methods to correct for microbial contamination when assessing in situ protein degradability of fresh forages1

“…As expected, the proportion of microbial N in the residue increased with incubation time (Alexandrov, 1998) and was more extensive for low-protein forages (Wanderley et al, 1999). Bacterial contamination of in situ residues as a function of incubation time has been fitted using an exponential function (Krawielitzki et al, 2006;Rodríguez and González, 2006). There were differences among labeling methods, with LAB giving the smallest estimates of microbial contamination for the incubation residues of the 3 forages.…”

“…The presence of protozoa and fungi in residual particles was confirmed by Lindberg et al (1984) and Elliott et al (1985). However, Krawielitzki et al (2006) recorded similar microbial contamination 3 a = readily soluble fraction (g N degraded/g N incubated); b = slowly degradable fraction (g N degraded/g N incubated); a + b = potential (asymptotic) degradability (g N degraded/g N incubated); k d = fractional degradation rate (h -1 ); dg = effective degradability (g N degraded/g N ingested); Δ = fractional change in the estimate of dg when residues are corrected for microbial contamination (in relation to the uncorrected or apparent value),…”

“…Mathers and Aitchison (1981) observed that residues remaining in the bags after incubation in the rumen were contaminated with microbial matter. The extent of microbial contamination is particularly high in forages with low N content and at longer incubation times (Krawielitzki et al, 2006;González et al, 2007). A correction for this contamination should be considered when assessing N degradability values.…”

Ruminal degradation of protein : implications for polluting emissions

“…Current results were also close to that of 70.9% shown by Varvikko and Lindberg (1985) for a 24 h-incubated barley straw residue and lower than that of 82% observed by Bernard et al (1988) for a 48 hincubated wheat straw. The increasing evolution of contamination over time is associated with the development of micro-colonies and agrees with previous results (Rodríguez and González, 2006;Nocek, 1988;Krawielitzki et al, 2006). The decreasing contamination order shown in general for total-N, NDIN and ADIN agrees with previous results obtained in several types of digesta samples, which showed a partial and accumulative microbial decontamination with the application of NDF and sequential ADF procedures Guevara-González et al, 2015).…”

Effect of Additives on In Vitro Intestinal Utilizable Crude Protein in Dairy Cows and Mobile Bag Nutrient Digestibility of Corn, Alfalfa and Whole Barley Silages

“…Individual bag residue disappearances were subsequently calculated based on the formula: Digestibility coefficient [21]=F-f/F; where, F is the amount of feed component (mg) in the bag and f is the amount of the feed component in the rumen or in the faeces (mg). Correction for bacterial contamination was estimated using exponential equation as described by Krawielitzki et al [22]. A max was estimated by treating a subsample of the residue with neutral detergent solution with the assumption that the residues only contained cell wall bound CP (estimated from neutral detergent insoluble N; NDIN) and microbial matter was soluble in neutral detergent [23].…”