In situstudy of the relevance of bacterial adherence to feed particles for the contamination and accuracy of rumen degradability estimates for feeds of vegetable origin

Abstract

An in situ study was conducted on four rumen-cannulated wethers to determine (using 15 N infusion techniques) the microbial contamination (mg bacterial DM or crude protein (CP)/100 mg DM or CP) and the associated error on the effective degradability of fourteen feeds: barley and maize grains, soyabean and sunflower meals, full-fat soyabean, maize gluten feed, soyabean hulls, brewers dried grains, sugarbeet pulp, wheat bran, lucerne and vetch-oat hays, and barley and lentil straws. The DM or CP contamination in residues (M) fitted to single exponential or sigmoid) was proposed to match this fit. Asymptotic values (m) varied from 2·84 % to 13·3 % and from 2·85 % to 80·9 % for DM and CP, respectively. Uncorrected results underestimated the effective degradability of both DM (P,0·05) and CP (P, 0·01). For CP, this underestimation varied from 0·59 % to 13·1 %, with a higher but unascertainable error for barley straw. Excluding maize grain, the microbial contamination of both DM and CP, and the associated underestimation of the effective degradability of CP, were positively related to the cellulose content of the feed. The error in the effective degradability of CP was also negatively related to the CP content and its apparent effective degradability (R 2 0·867). This equation allows easier and more accurate estimates of effective degradability, needed to improve protein-rationing systems. The current systems of protein rationing for ruminants require an accurate knowledge of the quantity of the microbial and feed proteins that reach the post-ruminal tract. The magnitude of both protein fractions is influenced by the rumen degradation of feeds included in the ration. In situ methods are the most common way to obtain estimates of effective degradability (ED). However, adherent micro-organisms that colonise and degrade feed particles simultaneously contaminate them. The resultant underestimate of the ED of crude protein (CP) or amino acids in vegetable feeds may be important as a consequence of the high N content in micro-organisms, although feed characteristics determining microbial adherence and the development and persistence of the micro-organisms may also influence this underestimate.In spite of these errors, uncorrected ED values are commonly employed in current systems, because the estimation of microbial contamination is a laborious, complex and expensive procedure. Although microbial attachment has been the subject of many types of research, quantitative and systematic in situ studies across a wide range of feeds are scarce (Michalet-Doreau & Ould Bah, 1989), and in most cases these have focused only on the effects of N contamination on ED estimates. Studies on microbial colonisation may, however, also contribute to a better knowledge of factors affecting feed degradation (McAllister et al. 1994) and microbial protein supply associated with feed particles, which represents an important contribution to the nutrition of the ruminant (Merry & McAllan, 1983, Rodríguez et al. 2003. The objectives of the present...

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).…”

“…Positive or negative differences of 15 N abundance between the whole feed and its insoluble fraction have been previously shown in a large collection of non-labelled feeds by Rodríguez and González (2006) which was explained by them by non-systematic differences in the 15 N fixation by the different tissues. Also, these authors showed that small differences This absorption will depend on the fibre polarity, which agrees with the lower reduction shown in SS than in wheat samples.…”

“…Isotopic markers such as 15 N have been used in in situ studies to solve the problems associated with this contamination by using two possible techniques: the rumen infusion of 15 N to a steady-state situation with the isolation of a sample of marked microorganisms (usually solid adherent bacteria, SAB) (Rodríguez and González, 2006) or the 15 N dilution technique using 15 N-enriched feedstuffs (Varvikko and Lindberg, 1985). Both techniques are subject to limitations and criticisms: for the first one, the possible lack of representability of the SAB sample for microorganisms adhered to specific feed particles and, for the second one, the incorporation to SAB of 15 N resulting from the colonised 15 N-enriched feed particles.…”

Potenciación de la respuesta productiva en rumiantes mediante el empleo de proteínas protegidas

“…Both overestimations are directly related to the extent of microbial contamination (Rodríguez and González, 2006), whereas the difference in intestinal disappearance between SAB and bypass compounds is also a major factor affecting ID overestimations , which is in agreement with the large overestimations shown in ID-CP of SP. Current values for SFM showed higher contaminations (4.0 and 3.1 times as average of the three meals for the DM and CP, respectively) than those observed in another SFM sample of a previous similar experiment carried out with the same doses of both acids .…”

“…The microbial proportions of N and DM in CS were determined as indicated by Rodríguez and González (2006) using SAB samples as reference; SAB isolates were lyophilised and analysed for DM, OM, N, 15 N/N and total glucose. Microbial proportions of OM and glucose were determined as the microbial DM content of CS samples × the concentration of these fractions in SAB expressed on DM.…”