Antimethanogenic effects of nitrate supplementation in cattle: A meta-analysis

Abstract

Supplementing a diet with nitrate is regarded as an effective and promising methane (CH 4 ) mitigation strategy by competing with methanogens for available hydrogen through its reduction of ammonia in the rumen. Studies have shown major reductions in CH 4 emissions with nitrate supplementation, but with large variation in response. The objective of this study was to quantitatively investigate the effect of dietary nitrate on enteric CH 4 production and yield and evaluate the variables with high potential to explain the heterogeneity of between-study variability using meta-analytical models. A data set containing 56 treatments from 24 studies was developed to conduct a meta-analysis. Dry matter (DM) intake, nitrate dose (g/kg of DM), animal body weight, roughage proportion of diet, dietary crude protein and neutral detergent fiber content, CH 4 measurement technique, and type of cattle (beef or dairy) were considered as explanatory variables. Average DM intake and CH 4 production for dairy cows (16.2 ± 2.93 kg/d; 311 ± 58.8 g/d) were much higher than for beef cattle (8.1 ± 1.57 kg/d; 146 ± 50.9 g/d). Therefore, a relative mean difference was calculated and used to conduct random-effect and mixed-effect model analysis to eliminate the large variations between types of animal due to intake. The final mixed-effect model for CH 4 production (g of CH 4 /d) had 3 explanatory variables and included nitrate dose, type of cattle, and DM intake. The final mixed-effect model for CH 4 yield (g of CH 4 /kg of DM intake) had 2 explanatory variables and included nitrate dose and type of cattle. Nitrate effect sizes on CH 4 production (dairy: −20.4 ± 1.89%; beef: −10.1 ± 1.52%) and yield (dairy: −15.5 ± 1.15%; beef: −8.95 ± 1.764%) were significantly different between the 2 types of cattle. When data from slow-release nitrate sources were removed from the analysis, there was no significant difference in type of cattle anymore for CH 4 production and yield. Nitrate dose enhanced the mitigating effect of nitrate on CH 4 production and yield by 0.911 ± 0.1407% and 0.728 ± 0.2034%, respectively, for every 1 g/kg of DM increase from its mean dietary inclusion (16.7 g/kg of DM). An increase of 1 kg of DM/d in DM intake from its mean dietary intake (11.1 kg of DM/d) decreased the effect of nitrate on CH 4 production by 0.691 ± 0.2944%. Overall, this metaanalysis demonstrated that nitrate supplementation reduces CH 4 production and yield in a dose-dependent manner, and that elevated DM intake decreases the effect of nitrate supplementation on CH 4 production. Furthermore, the stronger antimethanogenic effect on CH 4 production and yield in dairy cows than in beef steers could be related to use of slow-release nitrate in beef cattle.

Full adoption of the most effective strategies to mitigate methane emissions by ruminants can help meet the 1.5 °C target by 2030 but not 2050

“…Several reviews indicate that animal and feed management, diet formulation, and rumen manipulation strategies could significantly decrease enteric CH 4 emissions ( 12 , 16 , 17 ). However, previous studies consisted of qualitative reviews ( 12 ), examined the quantitative effects of a single mitigation strategy ( 18 – 20 ), or compared CH 4 yield (CH 4 Y; CH 4 per unit of feed intake) between multiple mitigation strategies ( 17 ). Methane yield is only one relevant measure, and other major CH 4 emission and animal performance metrics must be considered to determine the effectiveness and feasibility of mitigation strategies.…”

Effects of calcium ammonium nitrate fed to dairy cows on nutrient intake and digestibility, milk quality, microbial protein synthesis, and ruminal fermentation parameters

“…− has been established as an effective feed additive for mitigating CH 4 emissions in ruminants (Lee and Beauchemin, 2014;Beauchemin et al, 2020;Feng et al, 2020). However, studies aiming to evaluate milk characteristics such as antioxidant capacity and residues of NO 3 − and NO 2 − in response to NO 3 − supplementation are still needed, due to the importance of milk for human consumption.…”

“…Nitrate (NO 3 − ) compounds have been explored as feed additives to decrease methane (CH 4 ) production and as dietary NPN sources in ruminants. Recently, Feng et al (2020), using a meta-analytical approach, reported the efficacy of NO 3 − supplementation (mean = 16.7 g/kg of DM) at reducing CH 4 yield (g/DMI) in both dairy cows (15.5 ± 1.15%) and beef cattle (8.95 ± 1.76%). Methane mitigation with NO 3 − occurs because of its role as an alternative metabolic hydrogen ([H]) sink in the rumen, because the reduction from NO 3 − to NH 3 is more thermodynamically favorable than the use of CO 2 to synthesize CH 4 .…”

Strategies to mitigate enteric methane emissions by ruminants - a way to approach the 2.0°C target.

“…Another meta-analysis found similar effects of nitrate on daily CH4 emissions (-15%) 39 . Nitrate has also been shown to decrease daily CH4 emissions and CH4Y in a dose-response manner with no loss of effectiveness over and effectively decreased CH4 over the long-term 40,41 . Similar to 3-NOP, nitrate was more effective in decreasing daily CH4 emissions and CH4Y in dairy than in beef cattle 39 .…”

“…Acclimatization of animals to dietary nitrate is required to avoid methemoglobinemia, but rumen adaptation can be lost within three weeks if nitrate is not continuously fed 43 . Simultaneous sulfate supplementation has been shown to help protect cattle against nitrate toxicity 40 . Nitrate supplementation may increase enteric and possibly manure nitrous oxide emissions 44 .…”