Abstract
Ruminants are responsible for a large proportion of agricultural greenhouse gas emissions in the form of methane. This can be managed. It is a global initiative to increase productivity of the livestock sector to meet a growing population, but with emphasis on decreasing enteric methane to achieve emissions targets. We investigated the marine red macroalga (seaweed) Asparagopsis taxiformis as a feed ingredient to fundamentally eliminate enteric methane in beef cattle fed a high grain diet and provide evidence of improved livestock production performance. Asparagopsis was included in the feed of Brahman-Angus cross steers at 0.00%, 0.05%, 0.10%, and 0.20% of feed organic matter. Emissions were monitored in respiration chambers fortnightly over 90 d of treatment, steers were weighed weekly prior to feeding, feed intake monitored daily, rumen fluid samples collected in conjunction with respiration chambers for assessment of rumen function, feces were collected for bromoform residue analysis, and meat, organ, and fat were collected post slaughter for residue analysis and sensory evaluation. Steers receiving 0.10% and 0.20% Asparagopsis demonstrated decreased methane up to 40% and 98%, and demonstrated weight gain improvements of 53% and 42%, respectively. There was no negative effect on daily feed intake, feed conversion efficiencies, or rumen function, and no residues or changes in meat eating quality were detected. Commercial production of Asparagopsis could create new economies, and with low inclusion rates of this seaweed in ruminant diets the industry has the potential to revolutionize management of greenhouse gas emissions across the ruminant livestock sector with complementary benefits to the environment, and economy of the wider agriculture sector. © 2020 Commonwealth Scientific and Industrial Research Organisation. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4. 0/).
Generated Summary
This research investigates the potential of the marine red macroalga (seaweed) *Asparagopsis taxiformis* as a feed ingredient to mitigate methane emissions and improve productivity in ruminant livestock agriculture. The study employed a controlled in vivo experiment using Brahman-Angus cross steers fed a high-grain diet. Steers were subjected to four different inclusion levels of *Asparagopsis* (0.00%, 0.05%, 0.10%, and 0.20% of feed organic matter) over a 90-day period. The research involved monitoring methane and hydrogen emissions, feed intake, weight gain, rumen metabolites, meat quality, and the presence of bromoform residues in animal tissues. The methodology included controlled respiration chambers for gas measurements, individual feeding regimes, and regular weighing of the steers. The primary goal was to determine the effectiveness of *Asparagopsis* in reducing methane production and enhancing the overall performance of beef cattle under feedlot conditions. The study’s design aimed to provide a comprehensive characterization of *Asparagopsis* as an antimethanogenic feed ingredient, addressing its impact on both emissions and livestock productivity.
Key Findings & Statistics
- The study found that the inclusion of *Asparagopsis* significantly decreased methane emissions. At the 0.10% and 0.20% inclusion levels, methane was reduced by up to 40% and 98%, respectively.
- Steers receiving the 0.10% and 0.20% *Asparagopsis* demonstrated weight gain improvements of 53% and 42%, respectively.
- The average CH4 and H2 emissions showed significant changes. As the seaweed inclusion increased, CH4 production decreased significantly (P = 0.008). Compared to the Control group, CH4 production decreased by 9%, 38%, and 98% for the Low, Mid, and High inclusion levels, respectively.
- Enteric emission of H2 increased significantly (P = 0.006) with increasing seaweed inclusion. The increases were 0%, 380%, and 1700% for the Low, Mid, and High inclusion levels, respectively, compared to the Control group.
- The ADWG and FCR were analyzed for the full 90 d treatment period and the concluding 60 d. ADWG increased after the 90 d treatment period (P = 0.010).
- The Mid and High inclusion levels showed LW increases of 137 kg and 130 kg, resulting in an increased ADWG of 26% and 22%, respectively.
- The concluding 60 d showed significant ADWG (P = 0.027). The LW increases were 81 kg and 75 kg for the Mid and High levels, leading to ADWG improvements of 51% and 42%, respectively.
- There was no significant change in ruminal tVFA due to the inclusion of Asparagopsis in the diet of Brangus steers (P = 0.176).
- Acetate tended to be reduced compared to the Control group with 4%, 14%, and 20% reduction for the Low, Mid, and High inclusion levels, respectively.
- The acetate:propionate ratio (A:P) was significantly and linearly reduced (P = 0.026).
Other Important Findings
- The study demonstrated a linear and quadratic decrease in methane production with increasing levels of *Asparagopsis* inclusion.
- Hydrogen emissions increased with increasing seaweed inclusion, although there was no detrimental effect on DMI or rumen function.
- The inclusion of *Asparagopsis* did not negatively affect daily feed intake, feed conversion efficiencies, or rumen function.
- There were no residues or changes in meat eating quality detected, and commercial production of *Asparagopsis* could create new economies.
- Inclusion of *Asparagopsis* in the diet did not affect the meat eating quality, tenderness, juiciness, flavor, consumer satisfaction, or overall liking of the meat.
- Bromoform, the active compound, was not detected in any meat, kidney, fat, or feces samples.
Limitations Noted in the Document
- The study was conducted on a relatively small sample size, which may limit the generalizability of the findings.
- The study was conducted over a 90-day period, and longer-term effects of *Asparagopsis* inclusion were not evaluated.
- The study focused on a specific breed of cattle (Brangus steers) fed a high-grain diet; the results may not be directly applicable to other breeds or feeding systems.
- The study did not investigate the optimal inclusion level of *Asparagopsis* in different diets.
- Variations in the bromoform content of the *Asparagopsis* product used in the study could affect the results.
Conclusion
The findings of this study highlight the potential of *Asparagopsis taxiformis* as a promising tool for mitigating greenhouse gas emissions in the beef cattle industry while simultaneously improving productivity. The study demonstrated that the inclusion of *Asparagopsis* in a high-grain diet resulted in a substantial reduction in methane emissions, with significant improvements in weight gain. The authors conclude that *Asparagopsis* is a most promising option to achieve carbon neutrality in the livestock sector in the next decade. The study underscores the importance of reducing methane emissions from ruminant livestock production. The results suggest that *Asparagopsis* could create new economies and revolutionize management of greenhouse gas emissions across the ruminant livestock sector. The integration of *Asparagopsis* could help the red meat industry move towards carbon neutrality and improve beef cattle performance. The research emphasizes that the small inclusion level of Asparagopsis is advantageous in development of consistently high quality supply to make sizeable changes in the agriculture GHG emissions inventory. The study’s outcomes support the theory of beneficial redistribution of energy otherwise lost as CH4, leading to improved ADWG and FCR. The absence of negative impacts on meat quality and the absence of bromoform residues further enhance the viability of *Asparagopsis* as a feed ingredient.