Stable Isotope Labeled n-Alkanes to Assess Digesta Passage Kinetics through the Digestive Tract of Ruminants

Daniel Warner,Jan Dijkstra,Michel J H Breuer,Wilbert F Pellikaan,Luis M M Ferreira,Robert J Forster

doi:10.1371/journal.pone.0075496

Abstract

We describe the use of carbon stable isotope (13C) labeled n-alkanes as a potential internal tracer to assess passage kinetics of ingested nutrients in ruminants. Plant cuticular n-alkanes originating from intrinsically 13C labeled ryegrass plants were pulse dosed intraruminally in four rumen-cannulated lactating dairy cows receiving four contrasting ryegrass silage treatments that differed in nitrogen fertilization level (45 or 90 kg nitrogen ha−1) and maturity (early or late). Passage kinetics through the gastrointestinal tract were derived from the δ13C (i.e. the ratio 13C:12C) in apparently undigested fecal material. Isotopic enrichment was observed in a wide range of long-chain n-alkanes (C27–C36) and passage kinetics were determined for the most abundant C29, C31 and C33 n-alkanes, for which a sufficiently high response signal was detected by combustion isotope ratio mass spectrometry. Basal diet treatment and carbon chain length of n-alkanes did not affect fractional passage rates from the rumen (K 1) among individual n-alkanes (3.71–3.95%/h). Peak concentration time and transit time showed a quantitatively small, significant (p≤0.002) increase with carbon chain length. K 1 estimates were comparable to those of the 13C labeled digestible dry matter fraction (3.38%/h; r = 0.61 to 0.71; p≤0.012). A literature review has shown that n-alkanes are not fermented by microorganisms in the rumen and affirms no preferential depletion of 13C versus 12C. Our results suggest that 13C labeled n-alkanes can be used as nutrient passage tracers and support the reliability of the δ13C signature of digestible feed nutrients as a tool to measure nutrient-specific passage kinetics.

Highlights

Production animals need to be fed according to their nutritional requirements in order to reach their maximum performance, reduce the loss of waste products into the environment from undigested feed nutrients, and prevent nutrient-related disorders due to an unbalanced or insufficient supply of nutrients
Knowledge on the behavior of ingested feed nutrients in the different compartments of the gastrointestinal tract is essential to understand the fate of nutrients and related digestive mechanisms [1]
In ruminants, which are adapted to yield energy from poor-quality forages, the reticulorumen is the main site of fermentative degradation of nutrients through the action of microorganisms, mixing of the ingesta and particle size reduction

Summary

Introduction

Production animals need to be fed according to their nutritional requirements in order to reach their maximum performance, reduce the loss of waste products into the environment from undigested feed nutrients, and prevent nutrient-related disorders due to an unbalanced or insufficient supply of nutrients. Knowledge on the behavior of ingested feed nutrients in the different compartments of the gastrointestinal tract is essential to understand the fate of nutrients and related digestive mechanisms [1]. Once ingested feed particles reach a specific particle size [2] and specific density [3], they pass in aboral direction into the following digestive compartment at specific fractional rates (i.e., as a fraction per hour; %/h) depending on a number of feed and animal characteristics [4,5]. Knowledge on the fractional passage rate from the reticulorumen may be used to predict the extent of degradation and excretion of nutrients [1]. Quantitative knowledge on feed- and nutrient-specific passage kinetics are limited

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