Methane Emissions from Ruminant Livestock in Ethiopia: Promising Forage Species to Reduce CH4 Emissions
Round 1
Reviewer 1 Report
Dear Authors,
This paper reports an interesting evaluation of promising forage species to reduce methane emissions from ruminant livestock in Ethiopia and enhance forage quality and then production.
The authors highlight several limitations due to pedoclimatic factors, which hinder Ethiopian farmers, especially in some areas of the country, from obtaining adequate productions to satisfy the food needs of livestock.
At the same time, they underline how animal husbandry, in Ethiopia as well as in many other countries of the world, has a significant impact on methane emission.
The authors have an ambitious and noteworthy goal, to try to identify a possible solution to the two problems presented. the scarcity of food for livestock is considered a factor that negatively affects both the productive performance of the animals and the "polluting" emissions (kg CO2 eq. per kg of milk) compared to animals with an adequate diet.
The paper is well structured, with an appropriate bibliography, experimental apparatus and statistical analysis, but I have a question:
In the discussion of Tables 4 and 5 the authors say that a low production of methane can derive from the presence of secondary metabolites that inhibit its formation. Moreover, in the discussion of Table 5 it is said that methane production is not always well correlated with the chemical composition of feeds. The question: is there a risk that forages or feeds (not just those tested but in general) that produce less methane, then provide less nutriment to the animals, compromising the promising results of this study? Could be an assessment for further studies?
Author Response
Dear Reviewer,
We appreciate your encouraging comments and valuable feedbacks. We have considered your comments, and we have revised our manuscript accordingly. We have included the line numbers (in brackets) in the revised manuscript to help you identify our changes. Please find our responses in the attached file below.
Kind regards,
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper presents important problems concerning assessment of some factors, which decide about environment including animal farms as a source of harmful gases, i.e. methane and the others.
But there is possible to put some questions / problems concerning the reviewed material.
It is not given in details, what is included by the names "animal category" and "animal species" in the Materials and Methods chapter. Moreover, there is given "livestock population", so it should be explained by Authors, what data are included by each name. Another way the equation (1) includes the name "animal type (T)" and the "T" is given as species/livestock category, so - from my point of view - it is little confusing to understand / recognize some relationship between "category", "species", "type" and livestock.
Generally, livestock population was considered according to Central Statistical Authority, but it is not given information, how to understand "population". Is it population of matured animals or younger group of animals, too ? Of course, there is possible to identify some data in the Table 1, where few animal groups were distinguished, but information about considered animal categories should be included in the chapter: Materials and Methods. In my opinion it can be better to use LU (livestock unit) for the carried out analyses. Including LU it is possible to more correctly consider population of ruminant livestock and particular group of animals taking nutritional requirements as a basis.
It is the question concerning the data given in the Table 1: Do population data include average population per year or population at the end of year ? Such information should be given in the description concerning the animal population taken in the calculations.
Small letters in the Table 2 should be explained. It is written under the Table 2 "Means within a column with different or no letters are significantly different (P < 0.05)" but there should be also information, how to interprete: a, b, c and d. The same remark concerns the Tables 3 and 4.
The paper includes results of chemical analyses on some plants used in the ruminant livestock feeding, taking into account CH4 concentration. To calculate effect of CH4 concentration on the emission level in animal / ruminant livestock production there will be important to include share of particular components in the feeding dose given for animals. Generally, there is not so many information in the paper about feeding systems used in Ethiopian farms with the ruminant livestock. Some information about TMR (if used) in the farms and content / share of particular components can give results of calculations more exact. This problem inspires another question: Which plants / feed (fodder) was included to calculate enteric CH4 emissions from ruminant livestock in Ethiopia, given in Table 1 ? In my opinion it is important information to compare the data received in the carried out investigations.
It is another question concernig farmers’ preferences and ranking of the studied forage species: Where farmers asked (before conducted survey), if they know all considered plants or they have any knowledge about the plants assessed in the survey ? Such information should be given in the paper / materials and methods chapter.
It can also be interesting / valuable to give in the Materials and Methods chapter information about dominance cattle / sheep / goat breeds kept in Ethiopia.
In some papers / articles given in the References chapter there is lack of basic data like Vol. ... ? and pages ... ? Eg.: Kebreab, E.; Clark, K.; Wagner-Riddle, C.; France, J. Methane and nitrous oxide emissions from Canadian animal agriculture: A review. Canadian Journal of Animal Science 2006. It is necessary to round out the proper data.
Author Response
Dear Reviewer,
We appreciate your encouraging comments and valuable feedbacks. You raised important issues and your inputs are very helpful for improving our manuscript. We agree with almost all your comments, and we have revised our manuscript accordingly. We have included the line numbers (in brackets) in the revised manuscript to help you identify our changes. Please find our responses in the attached file below.
Kind regards,
Author Response File: Author Response.docx
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
In this paper the authors present an estimate of methane emissions from livestock production in Ethiopia and evaluate the potential of some native forages to reduce these emissions. They have chosen to take a tier1 approach to emissions estimates, along with in vitro methane production estimates. These methods clearly give an indication of which forages might be potentially useful and I see this paper as an early starting point for further study. Data on native forages in African contexts is sorely lacking with most research coming out of Europe and North America to date. I therefore see this as a very important paper.
In addition to the in vitro study, the authors have explored local farmer's attitudes towards these forages. This is in my opinion a particular strength of the study and sets this paper apart from the many other similar studies around the world.
Overall my opinion is that this is an important and interesting paper. I only have a few questions for clarification which when addressed will make the arguments presented even clearer and more useful :
Section 2.1: you mention in the introduction the diversity of livestock systems, yet you use only one emissions factor for the whole country. What are some of the limitations of this method, and what level of uncertainty can we expect in the estimated produced?
Section 2.2: why were plant samples pooled for each species? Statistically this reduces your sample size to N=1. How much variation is there in plant chemistry (in my experience this can be quite considerable)? How big of a sample was harvested and how were plants selected? To my mind this is the weakest point in your study. You are attempting to make inferences about methane mitigation for the whole of Ethiopia based on just one sample run in duplicate. This allows no estimate of variability which must be considerably high. What are your thoughts on the limitations of this approach and why did you choose such a limited sample size?
Section 3.1: you mention the change in methane emissions is due to changing numbers of livestock But why are livestock numbers changing? What are the drivers for these trends in Ethiopian agriculture?
Table 2 and 3: you technically only have one sample of each plant species, analysed in duplicate, so I'm not convinced that any statistical analysis is really valid here. I feel this is a shame.
Line 348: plants with higher CP, are these also luguminous? Other studies have shown relationship between N and CH4 and also potential for legumes to reduce CH4. Can these studies inform your discussion here?
Line 358-359: her you suggested that lignin can be beneficial in reducing CH4, but earlier you say lignin reduced digestibility which must have a negative impact on production and hence the opposite effect on emission per unit product. Can you clarify this conundrum a bit better here?
Author Response
Dear Reviewer,
We would like to thank for your precious time and thoughtful review of our manuscript. Please find our responses in the attached file.
Best,
Yonas Berhanu
Author Response File: Author Response.docx
Reviewer 2 Report
Because of the importance of reducing greenhouse gas emissions from agriculture while improving food production, the information in this manuscript could be a significant contribution to the literature. However, before publication, there seem to be several items that need to be addressed. First, because forage composition and fermentation characteristics are affected by the parts of the plants sampled and the maturity of the plants, the authors should be much more detailed in their descriptions of sampling procedures. Second, in order to conduct statistical analyses of the data for broader interpretation to the population of plants, there needs to be proper replication the data. Therefore, the authors need to describe the experimental design, particularly replication, in much more detail. Third, it is unclear how the different fermentation times were used in the quantification of methane production. Beyond these points, the part of the manuscript dealing with the calculation of total methane production from ruminant livestock in Ethiopia while interesting doesn’t seem to address the main objective of the manuscript; what forages can be used to reduce methane emissions. Additional comments are included in the attached file.
Comments for author File: Comments.docx
Author Response
Dear Reviewer,
We appreciate your valuable comments and constructive suggestions. We hope that you will find our responses to your comments satisfactory, and we are willing to finish the revised version of the manuscript including any further suggestion that you may have. Please find our point-by-point responses in the attached file.
Best,
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Because this manuscript address the important subject of GHG emissions and presents a novel approach to mediate methane emissions, it had the potential to be a significant contribution to the literature. The authors did a good job addressing and revising most of my concerns. However, the experiment has a critical error that makes publication of the paper questionable. Because the investigators pooled all of the samples from an individual species, they could not statistically analyze the differences between species. The authors attempted to address this by saying that they didn't feel that there would be differences between individual samples and, therefore, pooling was justified. But they added that readers should interpret their results carefully. They did conduct a statistical analysis using the variation in the replications of the laboratory analysis. This allowed them to put different letters on the means in the tables, giving readers the impression that there were or were not differences between species. However, the purpose of statistical analysis should be evaluating the variation within the population of plants and not the variation in the population of laboratory analyses. Thus, publication of the paper as a traditional research paper seems questionable.
