Effects of correcting for microbial contamination and the use of sodium sulphite in neutral detergent fibre analyses on the ruminal fibre degradability of several feeds

Abstract

Sodium sulphite is used in an optional way to remove insoluble proteins from neutral detergent fibre (NDF) residue. To determine whether the recovery of both NDF and insoluble nitrogen (N) in NDF solution (NDIN) are altered by its use, both parameters were measured in a set of 12 feeds, including cereal grains: maize (MG), rye (RG) and wheat (WG); cereal co-products: maize gluten feed (MGF), distilled dried grains from barley (DDGB) and wheat (DDGW) and wheat bran (WB); protein concentrates: rapeseed meal (RSM) and expeller palm kernel (EPK); dehydrated sugar beet pulp (DBP) and oat (OH) and ryegrass (RGH) hays. Associated effects on the in situ effective degradability (ED) of both NDF and NDIN were also studied in DDGW, WB, RSM, EPK, DBP, OH and RGH. Also, ED of acid detergent fibre (ADF) and its N (ADIN) were studied in hays. Errors due to microbial contamination in the rumen on the ED of NDF, ADF, NDIN and ADIN were also established in these last seven samples using 15 N infusion methods. Three rumen and duodenum cannulated wethers were used in the study. The sulphite use in NDF solution led to reductions (DDGB, DDGW, RSM and OH) and increases (RG, WG, WB and DBP) of the NDIN proportion, as well as the contribution of crude protein to NDF. These variations were associated with irregular effects on NDF residues and on ED of both NDIN and NDF. As a consequence, sulphite use does not assure the reduction of the insoluble protein contamination and it may even increase it. This methodology may also alter the degradability estimates of NDIN or NDF. Mean ruminal microbial contamination in NDF was 7·0, 10·8, 13·3, 5·4, 12·0, 35·3 and 20·0 g/kg in WB, DDGW, RSM, EPK, DBP, OH and RGH, respectively. The associated contents of microbial N in NDIN were: 59·3, 29·9, 26·2, 19·8, 37·3, 441 and 150 g/kg, respectively. Microbial contamination in ADF and ADIN (g/kg) was 3·6 and 94·5 in OH and 1·7 and 41·2 in RGH. Not correcting this contamination led to consistent undervaluations of ED of NDIN and NDF in all tested feeds, although errors only reached significance for NDIN in hays and DBP. Microbial-corrected ED of NDIN was 0·685, 0·826, 0·481, 0·389, 0·166, 0·718 and 0·425 in WB, DDGW, RSM, EPK, DBP, OH and RGH, respectively, whereas values for ADIN were 0·504 (OH) and 0·469 (RGH).

Ruminal degradation of protein : implications for polluting emissions

“…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). The exception to this behaviour observed at 4 h of incubation in SS and WG may be associated with the dilution of microbial N in a still high N content of incubated residues, which decreased from total-N to ADIN.…”

“…In the present study the calculation of degradability values was made taken into account only the rumen evacuation rate (5%/h) but not the comminution rate whereas in those of and Guevara-González et al (2015) these both rates were considered. The use of both rates for the calculation of degradability would result in higher values, especially for fibrous highly-lignified feeds such as wheat straw or sunflower seed hulls, which also have low comminution rates.…”

“…Regrettably, these estimates are biased by the contamination with adherent microorganisms during feed particle residence time in the rumen-reticulum because procedures to isolate neutral detergent (NDF) and acid detergent (ADF) fibres do not allow the total detachment of ruminal adherent microorganisms. This may lead to under-estimating the ruminal degradation of cell wall-bound N, especially for NDIN (Arroyo and Gonzalez, 2013;Guevara-González et al, 2015).…”

Ruminal degradation of cell wall associated nitrogenous compounds of several15N-labelled feeds

“…Regrettably, these estimates are biased by the contamination with adherent microorganisms during feed particle residence time in the rumen‐reticulum because procedures to isolate neutral detergent (NDF) and acid detergent (ADF) fibres do not allow the total detachment of ruminal adherent microorganisms. This may lead to under‐estimating the ruminal degradation of cell wall‐bound N, especially for NDIN …”

“…This may lead to under-estimating the ruminal degradation of cell wall-bound N, especially for NDIN. 1,2 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) 3 or the 15 N dilution technique using 15 N-enriched feedstuffs. 4 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.…”