Net transfer of nutrients to the duodenum and disappearance ofn-alkanes in the reticulo-rumen and the hindgut of sheep fed grass/legume combinations

Abstract

An experiment was carried out to examine the effect of increasing the proportion of Wimmera ryegrass hay in a lucerne hay-based diet on net transfer of nutrients to the intestine, and on the disappearance of n-alkanes in the reticulo-rumen and the hindgut of sheep. Following a latin square design, four adult ewes were fed 1:0, 0·33:0·67, 0·67:0·33 and 0:1 proportions of legume and grass. Increasing the proportion of ryegrass in the diet linearly decreased the intake of DM (P¼0·017), organic matter (P¼0·021) and N (P¼ 0·001). However, neutral-detergent fibre intake was not affected (P¼ 0·148), nor was its digestibility coefficient (P.0·10). Diet had no effect on duodenal flows of nutrients (P.0·10), although the proportion of N intake (NI) recovered at the duodenum as non-NH 3 N (NAN) increased linearly with Lolium rigidum in the diet (P¼0·002). Full recovery of NI as NAN was achieved at NH 3 concentrations in the rumen below 110 g/l. Microbial N contribution to NAN varied in a quadratic manner (P, 0·05) with the proportion of grass in the diet, although efficiency of microbial synthesis was not affected (P. 0·10). Duodenal recovery of consumed n-alkanes was not affected by diet and was complete for those present in higher concentrations in the forages. Isolated rumen bacteria contained significant amounts of n-alkanes, contributing to the duodenal flow of these hydrocarbons in variable proportions depending on the diet consumed.Key words: n-Alkanes: Duodenum: Nutrients: Rumen bacteria Net transfer of ingested protein to the duodenum (in the form of microbial protein, undegraded plant protein and endogenous protein) is complete only when the plants contain approximately 210 g crude protein (CP)/kg digestible organic matter (DOM) or less (1) . Above this threshold, there is net loss of protein with potentially large amounts of ingested N lost as NH 3 across the rumen wall. Legumes usually exceed this CP content, and hence including a grass in the diet might minimise N losses. The amount of protein reaching the abomasum when animals are fed different grass/legume mixtures (2) is largely unknown, with most of the work having been carried out with silages and dairy animals (3 -5) . Lucerne and Wimmera ryegrass (Lolium rigidum) are important resources of integrated sheep farming systems in many semi-arid areas of the world, but there is no information about net transfer of N to the duodenum when these are fed in combination.The use of n-alkanes as markers of diet selection and intake in grazing animals (6,7) is based on evidence that faecal recovery is related to chain length (6 -8) , which allows correcting for the incomplete faecal recovery of a determined hydrocarbon by dosing a selected alkane of similar chain length. Incomplete recovery of n-alkanes in faeces can be due to losses in the reticulo-rumen, in post-ruminal compartments or in both. Studies dealing with ruminal disappearance of n-alkanes are scarce (8 -11) , but they suggest that losses in the reticulo-rumen are minimal, if any. If this is th...

Technical note: Evaluation of markers for estimating duodenal digesta flow and ruminal digestibility: Acid detergent fiber, sulfuric acid detergent lignin, and n-alkanes

“…The recovery of n-alkanes in the feces was (mean ± SD) 0.63 ± 0.11, 0.47 ± 0.09, and 0.76 ± 0.11 for C 31 , C 32 , and C 33 , respectively. Except for C 32, these recovery values were similar to those reported by Morais et al (2011) and Keli et al (2013). Because a very low recovery of C 32 was obtained, the use of the relationship between the amount of orally dosed C 32 and its concentration in the duodenal digesta resulted in a negative ruminal DM digestibility.…”

Methane production, nutrient digestion, ruminal fermentation, N balance, and milk production of cows fed timothy silage- or alfalfa silage-based diets

“…Bannink et al (2010) suggested that at a pH of approximately 6.3 (the average value observed in this study), fermentation of starch in the rumen results in less propionate production than at lower pH, which may contribute to explain the lack of changes in CH 4 production observed in our study. Carulla et al (2005), Keli et al (2013), and Hammond et al (2013) also reported that replacing partially or completely ryegrass with alfalfa (fresh or hay) in sheep diets had no significant effect on ruminal pH, total VFA concentration, or molar proportion of acetate or propionate. Other studies observed an increase (Kammes and Allen, 2012) or a decrease (Dewhurst et al 2003a;Vanhatalo et al 2009) in molar proportion of propionate in the rumen when legumes replaced grasses in dairy cow or sheep diets.…”

Does Replacing Maize with Barley Affect the Animal Performance and Rumen Fermentation, including Methane Production, of Beef Cattle Fed High-Concentrate Diets On-Farm?

“…The estimation of intake in group-and loose-housed animals using n-alkanes as markers was performed as in Keli et al [33], whereas the disappearance of DM and starch from polyester bags on time was fitted to the first-order kinetic equation described by Ørskov and McDonald [35]. The concentration of Yb in faeces was adjusted to a decreasing exponential function in which the slope represents the fractional rate of passage through the rumen [36].…”

“…Refusals in polyester bags were analysed for DM and starch content, whereas the concentration of Yb in samples of faeces was determined as described by Keli et al [33]. Cortisol in hair was determined as in Moya et al [34] using an ArborAssays kit (ArborAssays, Ann Arbor, MI, USA).…”