Dietary nitrate metabolism and enteric methane mitigation in sheep consuming a protein-deficient diet

Abstract

It 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.

Meta-analysis quantifying the potential of dietary additives and rumen modifiers for methane mitigation in ruminant production systems

“…3 B), which is a beneficial outcome for grazing systems. Moreover, dietary NO 3 - supplies non-protein nitrogen to the rumen biota, reducing the need for other dietary non-protein nitrogen sources ( Hulshof et al., 2012 ; Li et al., 2012 ; Villar et al., 2020 ). The overall reduction in MI (g CH 4 /kg of milk or weight gain) from NO 3 - inclusion ranged from 10.7% to 18.7% ( P < 0.01; n = 11, Fig.…”

Toxic Wasting Disorders in Sheep

“…Sheep may be exposed to nitrates by consuming nitrate accumulating plants, decaying organic matter, and/or certain fertilizers [ 6 ]. Recently, nitrate supplementation has been proposed as an effective method to reduce methane emissions by ruminants [ 16 ]. Some examples of nitrate accumulating plants and their effects are described later in this paper (see Section 3.4 Nitrate-Accumulating Plants).…”

Deferred grazing and supplementation with ammonium nitrate as strategy for greenhouse gas emissions mitigation

“…Nitrate (NO3-) work as an electron receptor (H+) in the rumen (LENG and PRESTON, 2010) reducing methane production as it competes with these microorganisms for hydrogen. Some microbes can reduce nitrate to nitrite and further to ammonia (LEWIS, 1951;IWAMOTO et al, 2002), confirming enteric methane mitigation by nitrate salts in rumen (NOLAN et al, 2010;VAN ZIJDERVELD et al, 2011;HULSHOF et al, 2012;LI et al, 2012;VILLAR et al 2020). Newbold et.…”

“…(2014 affirm that this occurs because, when transformed, the nitrate competes with the CH4 producing route, consuming H2 electrons and reducing methanogenic microorganisms, due to electrons availability lower than nitrite toxicity level for these microorganisms. Villar et al (2020) observed that NO3was an effective additive to reduce CH4 emissions, and a source of additional nitrogen (N) for microbial protein synthesis via N-recycling into saliva and the gut.…”