Effect of variation in the proportion of solid- and liquid-associated rumen bacteria in duodenal contents on the estimation of duodenal bacterial nitrogen flow

Abstract

The aim of this research was to examine to what extent variation in the relative proportions of solid-(SAB) and liquid-associated rumen bacteria (LAB) in duodenal bacteria have an impact on the estimation of duodenal flow of bacterial N. For this, four dairy cows were fed diets varying in forage: concentrate ratio (80:20, 65:35, 50:50 and 35:65). SAB and LAB were separated from rumen contents four h after the morning feeding. Adenine, cytosine and odd and branched-chain fatty acids were determined both in SAB and LAB and used to estimate bacterial N flow. Bacterial N flows were also calculated using a SAB:LAB ratio in duodenal bacteria, as estimated from the odd and branched-chain fatty acid pattern. Compared with calculations based on the estimated SAB:LAB ratio, estimations based on SAB or LAB only as a bacterial reference on average over-and underestimated bacterial N flow by 37 and 55 g N/d, respectively (P<0.05) when cytosine or adenine were used as bacterial marker. In contrast, due to the small differences in the OBCFA:N ratio between SAB and LAB, these differences were less than 15 g/d when OBCFA were used as bacterial marker. The results suggest that, depending on the marker used, changes in the proportions of SAB and LAB can have a substantial impact on estimated duodenal flow of bacterial N.

Apparent Recovery of Duodenal Odd- and Branched-Chain Fatty Acids in Milk of Dairy Cows

“…This lack of relationship was surprising, because there was a substantial increase in microbial yield at the duodenum in response to increasing concentrates (Moorby et al, 2006). Nonetheless, there was a strong correlation between the flows of purine bases and of OBCFA in duodenal digesta in this study (Vlaeminck et al, 2006). This suggests that, in contrast to the results of Vlaeminck et al (2005), milk OBCFA are not useful microbial markers.…”

“…A large number of studies over the last 40 yr have estimated microbial protein flow from the rumen using marker techniques and cannulated animals. Odd-and branched-chain fatty acids (OBCFA) are distinctive components of ru-men microorganisms (Harfoot, 1978) and have recently been used as markers of the microbial protein content within rumen and duodenal digesta (Vlaeminck et al, 2005(Vlaeminck et al, , 2006.…”

“…For example, there is relatively little information about the relative proportions of solid-and liquid-associated bacteria in duodenal digesta (Vlaeminck et al, 2006). The relatively constant ratio of OBCFA:N within solid-and liquid-associated bacteria (Vlaeminck et al, 2006) means that OBCFA may be more robust than conventional markers, such as purines (Vlaeminck et al, 2005).…”

The relationship between odd- and branched-chain fatty acids and microbial nucleic acid bases in rumen

“…However, these findings were limited to variations in dietary treatment. Vlaeminck et al [ 12 ] determined adenine, cytosine and odd and branched-chain fatty acids both in SAB and LAB and used them to estimate bacterial N flow in duodenal. The results suggested that, depending on the marker used, changes in the proportions of SAB and LAB can have a substantial impact on estimated duodenal flow of bacterial N. Vlaeminck et al [ 8 ] found that a large and independent dataset of OBCFAs could accuracy predict the molar proportions of volatile fatty acids in the rumen.…”