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Nolan, John V
- PublicationDietary nitrate metabolism and enteric methane mitigation in sheep consuming a protein-deficient dietIt was hypothesised that the inclusion of nitrate (NO3–) or cysteamine hydrochloride (CSH) in a protein deficient diet (4.8% crude protein; CP) would improve the productivity of sheep while reducing enteric methane (CH4) emissions. A complete randomised designed experiment was conducted with yearling Merino sheep (n = 24) consuming a protein deficient wheaten chaff control diet (CON) alone or supplemented with 1.8% nitrate (NO3–; DM basis), 0.098% urea (Ur, DM basis) or 80 mg cysteamine hydrochloride/kg liveweight (CSH). Feed intake, CH4 emissions, volatile fatty acids (VFA), digesta kinetics and NO3–, nitrite (NO2–) and urea concentrations in plasma, saliva and urine samples were measured. There was no dietary effect on animal performance or digesta kinetics (P > 0.05), but adding NO3– to the CON diet reduced methane yield (MY) by 26% (P = 0.01). Nitrate supplementation increased blood MetHb, plasma NO3 – and NO2– concentrations (P < 0.05), but there was no indication of NO2– toxicity. Overall, salivary NO3– concentration was greater than plasma NO3– (P < 0.05), indicating that NO3– was concentrated into saliva. Our results confirm the role of NO3– as an effective additive to reduce CH4 emissions, even in a highly protein-deficient diet and as a source of additional nitrogen (N) for microbial protein synthesis via N-recycling into saliva and the gut. The role of CSH as an additive in low quality diets for improving animal performance and reducing CH4 emissions is still unclear.
- PublicationNitrate and nitrite absorption, recycling and retention in tissues of sheep(Elsevier BV, 2021-07)
; ; ; Dietary nitrate is of increasing interest both for the pharmacological effects of its metabolites as well as its capacity to inhibit methanogenesis in the gut. A sequence of three experiments was conducted to investigate the absorption, metabolism and excretion of nitrate and nitrite through the gastrointestinal tract (GIT) of sheep, and to determine the fate of nitrate and nitrite in body fluids, tissues and faeces after intravenous dosing with 15N-labeled potassium nitrate (K15NO3) and with 15N-labeled sodium nitrite (Na15NO2). In Experiment 1, twelve female Merino sheep were assigned to one of two dietary treatments and adapted to the experimental diet over two weeks. Six sheep were fed a control diet of wheaten chaff mixture (600 g wheaten chaff plus 200 g wheat grain, CON) and six sheep were fed the CON diet with the inclusion of 18 g nitrate/kg DM (Nitrate). After acclimation to the diets, all sheep received a single intravenous dose of K15NO3 and were placed in metabolic cages for daily collection of total faeces and urine over 6 days. Experiment 2 studied movement of an intravenous dose of 15N in body fluids and tissues. Two sheep not adapted to dietary nitrate were dosed intravenously with K15NO3 or Na15NO2 and body fluids and tissue samples were collected 60 min after dosing. Finally, Experiment 3 was conducted to identify and quantify the major sites of nitrate and nitrite transfer within the body, focusing on absorption, partitioning and secretion into the GIT of anaesthetised sheep. A single dose of sodium nitrate (NaNO3) or sodium nitrite (NaNO2) was introduced into the rumen or abomasum or small intestine, and changes in nitrate and nitrite concentrations in other pools, including plasma, urine and saliva, were determined. Results from Experiment 1 showed that urinary recovery of 15N dose in urea after 46 h and total urinary recovery of 15N 141 h after dosing were greater in sheep fed the Nitrate diet relative to CON (P < 0.05). Recoveries of 15N in tissues indicated that nitrate and nitrite principally accumulated in the skin and muscle of sheep (Experiment 2). Finally, Experiment 3 indicated that nitrate and nitrite were rapidly absorbed from the rumen, abomasum and small intestine into the bloodstream. Nitrite was oxidized in plasma and the resultant nitrate was concentrated and recycled via saliva. Appearance of 15N in urinary urea confirmed the passage of plasma nitrate to the digestive tract, via saliva or transruminal flow to be reduced by gut biota to ammonia.
- PublicationDietary nitrate and presence of protozoa increase nitrate and nitrite reduction in the rumen of sheep(Wiley-Blackwell Verlag GmbH, 2020-09)
; ; ; ; ; Nitrate (NO3–) supplementation is an effective methane (CH4) mitigation strategy for ruminants but may produce nitrite (NO2–) toxicity. It has been reported that rumen protozoa have greater ability for NO3– and NO2– reduction than bacteria. It was hypothesised that the absence of ruminal protozoa in sheep may lead to higher NO2– accumulation in the rumen and a higher blood methaemoglobin (MetHb) concentration. An in vivo experiment was conducted with defaunated (DEF) and faunated (FAU) sheep supplemented with 1.8% NO3– in DM. The effects of rumen protozoa on concentrations of plasma and ruminal NO3– and NO2–, blood MetHb, ruminal volatile fatty acid (VFA) and ruminal ammonia (NH3) were investigated. Subsequently, two in vitro experiments were conducted to determine the contribution of protozoa to NO3– and NO2– reduction rates in DEF and FAU whole rumen digesta (WRD) and its liquid (LIQ) and solid (SOL) fractions, incubated alone (CON), with the addition of NO3– or with the addition of NO2–. The results from the in vivo experiment showed no differences in total VFA concentrations, although ruminal NH3 was greater (p < .01) in FAU sheep. Ruminal NO3–, NO2– and plasma NO2– concentrations tended to increase (p < .10) 1.5 hr after feeding in FAU relative to DEF sheep. In vitro results showed that NO3– reduction to NH3 was stimulated (p < .01) by incoming NO3– in both DEF and FAU relative to CON digesta. However, adding NO3– increased (p < .05) the rate of NO2– accumulation in the SOL fraction of DEF relative to both fractions of FAU digesta. Results observed in vivo and in vitro suggest that NO3– and NO2– are more rapidly metabolised in the presence of rumen protozoa. Defaunated sheep may have an increased risk of NO2– poisoning due to NO2– accumulation in the rumen.