Abstract
Ruminants, particularly dairy and beef cattle, contribute to climate change through mostly enteric methane emissions. Several mitigating options have been proposed, including the feed additive 3-nitrooxypropanol (3-NOP). The objectives of this study were to explain the variability in the mitigating effect of 3-NOP and to investigate the interaction between diet composition and 3-NOP dose, using meta-analytical approaches. Data from 13 articles (14 experiments) met the selection criteria for inclusion in the meta-analysis, and 48 treatment means were used for the analysis. Mean differences were calculated as 3-NOP treatment mean minus control treatment mean and then expressed as a percentage of the control mean. Three types of models were developed: (1) one including 3-NOP dose, overall mean, and individual covariate; (2) a combination of neutral detergent fiber (NDF), 3-NOP dose, and overall mean; and (3) one selected model from all combinations of up to 5 covariates, which were compared using a leave-one-out cross validation method. Models including only 3-NOP dose resulted in a significant reduction of 32.7%, 30.9%, and 32.6% for CH4 production (g/d), yield (g/kg dry matter intake), and intensity (g/kg energy-corrected milk), respectively, at an average 3-NOP dose of 70.5 mg/kg dry matter (DM). The greater the NDF content in the diet, the lower the reduction efficiency for a given 3-NOP dose. For 10 g/kg DM increase in NDF content from its mean (329 g of NDF/kg of DM) the 3-NOP effect on CH4 production was impaired by 0.633%, the 3-NOP effect on CH4 yield by 0.647%, and the 3-NOP effect on CH4 intensity by 0.723%. The analysis based on leave-one-out cross validation showed an increase in NDF and crude fat content reduces efficacy of 3-NOP and an increase in 3-NOP dose increases efficacy. A 1% (10 g/kg) DM decrease in dietary NDF content from its mean may increase the efficacy of 3-NOP in reducing CH4 production by 0.915%. A 1% (10 g/kg DM) decrease in dietary crude fat content from its mean enhances the efficacy of 3-NOP on CH4 production by 3.080% at a given dose and NDF level. For CH4 yield, next to 3-NOP dose, dietary NDF content and dietary crude fat content were included in the selected model, but also dietary starch content with an opposite direction to NDF and crude fat. The effect of 3-NOP dose on CH4 intensity was similar to its effect on CH4 production, whereas the effect of dietary NDF content was slightly lower. Expanding the previously published models with the newly available data published from trials since then improved model performance, hence demonstrating the value of regularly updating meta-analyses if a wider range of data becomes available.
Generated Summary
This meta-analysis investigated the effects of 3-nitrooxypropanol (3-NOP), a feed additive, on methane production, yield, and intensity in dairy cattle. The study utilized data from 13 articles (14 experiments), analyzing 48 treatment means to explain variability in the mitigating effect of 3-NOP and explore the interaction between diet composition and 3-NOP dosage. The research employed meta-analytical approaches, developing three types of models: one incorporating 3-NOP dose and individual covariates, a second combining neutral detergent fiber (NDF) and 3-NOP dose, and a third selected from multiple covariate combinations. The effects were evaluated based on the relative mean differences from control treatments, expressed as percentages. The analysis aimed to quantify the impact of 3-NOP on methane emissions, considering both the dose of the additive and the composition of the diet.
Key Findings & Statistics
- Models including only 3-NOP dose resulted in a significant reduction of:
- 32.7% for CH4 production (g/d)
- 30.9% for CH4 yield (g/kg dry matter intake)
- 32.6% for CH4 intensity (g/kg energy-corrected milk)
- The greater the NDF content in the diet, the lower the reduction efficiency for a given 3-NOP dose.
- For a 10 g/kg DM increase in NDF content from its mean (329 g of NDF/kg of DM):
- The 3-NOP effect on CH4 production was impaired by 0.633%.
- The 3-NOP effect on CH4 yield was impaired by 0.647%.
- The 3-NOP effect on CH4 intensity was impaired by 0.723%.
- The analysis based on leave-one-out cross validation showed:
- An increase in NDF and crude fat content reduces efficacy of 3-NOP.
- An increase in 3-NOP dose increases efficacy.
- A 1% (10 g/kg) DM decrease in dietary NDF content from its mean may increase the efficacy of 3-NOP in reducing CH4 production by 0.915%.
- A 1% (10 g/kg DM) decrease in dietary crude fat content from its mean enhances the efficacy of 3-NOP on CH4 production by 3.080% at a given dose and NDF level.
- For CH4 yield:
- Dietary NDF content and dietary crude fat content were included in the selected model.
- Dietary starch content also played a role, but with an opposite direction to NDF and crude fat.
- The effect of 3-NOP dose on CH4 intensity was similar to its effect on CH4 production, whereas the effect of dietary NDF content was slightly lower.
- The average DMI was 22.8 kg/d.
- The average CP (% of DM) was 17.0.
- The average crude fat (% of DM) was 4.2.
- The average NDF (% of DM) was 32.9.
- The average starch (% of DM) was 21.1.
- The average OM (% of DM) was 92.5.
- The average fermentable OM (% of DM) was 53.2.
- The average OM digestibility (% of OM) was 77.1.
- The average roughage proportion (% of diet DM) was 61.9.
- The average 3-NOP dose (mg/kg DM) was 70.5.
- The average CH4 production (g/d) was 361.0.
- The average MD CH4 production (g/d) was -135.0.
- The average relative MD CH4 production (% of control) was -31.6.
- The average CH4 yield (g/kg DMI) was 16.0.
- The average MD CH4 yield (g/kg DMI) was -5.5.
- The average relative MD CH4 yield (% of control) was -29.5.
- The average CH4 intensity (g/kg ECM) was 10.6.
- The average MD CH4 intensity (g/kg ECM) was -4.0.
- The average relative MD CH4 intensity (% of control) was -31.4.
Other Important Findings
- The study’s findings indicate that, in addition to 3-NOP dose, dietary NDF content significantly influences the effectiveness of 3-NOP in reducing methane emissions.
- The model for CH4 production included both dietary NDF and crude fat content.
- The selected model for CH4 intensity included 3-NOP dose and dietary NDF content.
- The study suggests the need to consider the range of dietary components (NDF, crude fat, starch) when determining the efficacy of 3-NOP.
- The researchers emphasize that the current findings are applicable for the typical ranges of the components within the database: 3-NOP dose (40 to 130 mg/kg DM), NDF (26.5% to 43.5% DM), and crude fat (approximately 3% to 6%).
- The study proposes the possibility of building more complex models for a more precise representation of mechanisms underlying methane emissions.
Limitations Noted in the Document
- The study acknowledges that its findings are based on the available data and that the relationships between diet composition and 3-NOP effects may not be fully understood.
- The current study uses an expanded database taking a wider range of NDF values into account and focuses on dairy studies only, which limits the scope.
- The range of crude fat was small (approximately 3%), and in addition, missing nutrient components were estimated with tabular values and fat source was not accounted for in the models. Therefore, the current assumptions of effects are efforts to explain the presented data-driven findings.
- The equations provided in the current study can be used to calculate CH4 emission reduction for 3-NOP-supplemented dairy cows and incorporated in protocols used for purposes such as carbon market or farm GHG accounting tools. Nevertheless, it is possible to build more complex models to attempt to better represent the underlying mechanisms and explain the findings of the present study.
- The researchers restricted their analysis to the experimental observations made and the usability of the model, given the limited dataset, and did not presume any underlying mechanisms or influencing factors.
Conclusion
The meta-analysis confirms the effectiveness of 3-NOP in mitigating CH4 emissions in dairy cattle, demonstrating reductions in production, yield, and intensity at an average dose of 70.5 mg/kg DM. The study underscores that the effectiveness of 3-NOP is influenced by diet composition, particularly NDF and crude fat content. The higher the NDF and crude fat content, the less effective 3-NOP becomes at reducing methane production. The impact of diet composition on the efficacy of 3-NOP implies that dietary strategies should be optimized to enhance the additive’s effectiveness. The equations generated in the study provide a tool for calculating methane emission reductions in dairy cows supplemented with 3-NOP. The study’s results support the importance of integrating diet composition details when evaluating 3-NOP’s impact on methane emissions. The study emphasizes the need for ongoing research, suggesting that future studies should explore the underlying mechanisms involved in methane production and the effects of different dietary components, potentially leading to more accurate predictive models.