Review Reports - Tomato Residue Silage as a Sustainable Feed for Lambs with Implications for Performance, Water Use and Meat Quality

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear author

After a thorough analysis, I conclude that the manuscript presents several issues that prevent its approval in its current form. The main critical points are:

Formatting and standardization errors: The units used are inconsistent (e.g., g/kg and g·kg⁻¹), and the references cited differ from those listed in the bibliography.
Materials and methods: The description of procedures is insufficient, making experiment reproducibility difficult. There are also methodological errors that compromise the validity of the results.
Discussion: The analysis of the results is superficial, lacking depth and proper contextualization within the literature.
Choice of journal and special issue: Submission to Sustainability does not appear appropriate for the manuscript’s content. Although the use of tomato by-products in animal feed may be considered sustainable, the title and objective suggest that the ensiling process would reduce or eliminate pesticides in the feed and animal meat, which was not tested. The authors used residue without pesticides, making it impossible to confirm the effectiveness and safety of the process if pesticide contamination were present.
Nutritional comparison and experimental fairness: From a nutritional standpoint, the diets provided to the animals were not balanced equally, clearly favoring the diet with tomato by-product silage. This compromises the validity of the comparison and biases the results obtained.

Note: Detailed comments are provided in the attached file, as the submitted manuscript version does not include line numbering.

In summary, the manuscript requires fundamental revisions in methodology, analysis, consistency of information, and alignment with the journal’s scope. It is recommended that the authors address all the points raised before resubmission.

Sincerely,

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English could be improved

Author Response

REVIEWER 1:

I believe the authors intended to assess and quantify the presence of pesticide residues in silage and in the meat of animals fed with such silages. However, the animals did not receive silage containing pesticides and, consequently, no residues were detected in the meat. This outcome contradicts the introduction, which states that contamination by pesticides is common in tomato industry by-products. In my view, the main shortcoming of the study was collecting by-product samples without first verifying the presence of pesticide contamination. Therefore, there is no justification for including the evaluation of pesticide residues in the title. In fact, both the title and the introduction suggest that the article would address two aspects simultaneously: the use of a by-product in sheep feeding and the presence of pesticide residues in silage and meat. In this sense, I believe the authors lost part of their focus between what was initially planned, what they expected to find, and what was actually observed. In my opinion, the article should be rewritten to focus exclusively on the feasibility of using an industrial by-product in animal feeding, emphasizing its potential to reduce food waste and lower production costs. At most, the text could include a brief consideration regarding the possibility of pesticide contamination, but this should not be the central focus of the study.

Response: We thank the reviewer for this observation and agree with the point raised. As the tomato residue used in this study was sourced from a large processing industry, it was not possible to preselect the material based on its pesticide contamination status. Nevertheless, we considered it relevant to screen for potential residues, since this aspect relates to meat quality and consumer safety. We would also like to clarify why the pesticide residue analysis was performed on the PMR silage rather than on the isolated tomato residue. The animals were fed the PMR silage, which included the tomato by-product mixed with other ingredients. Since the additional components were of commercial origin —sources that are generally not traceable for pesticide application—we considered it more appropriate to analyze the silage as a whole, as this better represents the material actually ingested by the animals. In line with the reviewer’s recommendation, we now present the pesticide residue analysis as complementary information rather than a central focus of the study. Accordingly, we have reduced its emphasis in the manuscript and removed any reference to pesticide residues from the title. The revised version now concentrates on two central aspects: (i) the feasibility of using an agro-industrial by-product in animal feeding, highlighting its contribution to sustainability by reducing food waste and production costs; and (ii) water use efficiency, which is essential for small ruminant production in semi-arid regions and strongly aligned with the United Nations Sustainable Development Goals.

After a thorough analysis, I conclude that the manuscript presents several issues that prevent its approval in its current form. The main critical points are:

Formatting and standardization errors: The units used are inconsistent (e.g., g/kg and g·kg⁻¹), and the references cited differ from those listed in the bibliography.

Response: I corrected.

Materials and methods: The description of procedures is insufficient, making experiment reproducibility difficult. There are also methodological errors that compromise the validity of the results.

Response: In the revised version, we have expanded the Materials and Methods section to provide a more detailed description of the experimental procedures, ensuring reproducibility. Specifically, we clarified the steps involved in silage preparation, feeding management, and water intake assessment. In addition, methodological consistency was strengthened by including appropriate references to support the procedure used for measuring water intake in individual pens.

Discussion: The analysis of the results is superficial, lacking depth and proper contextualization within the literature.

Response: In the revised version, we expanded the Discussion to provide deeper analysis and contextualization of the results within the existing literature. We incorporated additional studies on tomato byproduct silages, animal performance, water intake efficiency, and feed safety, highlighting both similarities and contrasts with our findings. We also strengthened the sustainability perspective, aligning the discussion with broader implications for small ruminant production in semi-arid regions.

Choice of journal and special issue: Submission to Sustainability does not appear appropriate for the manuscript’s content. Although the use of tomato by-products in animal feed may be considered sustainable, thetitle and objective suggest that the ensiling process would reduce or eliminate pesticides in the feed and animal meat, which was not tested. The authors used residue without pesticides, making it impossible to confirm the effectiveness and safety of the process if pesticide contamination were present.

Response: We revised the manuscript to avoid suggesting that ensiling itself reduces or eliminates pesticide residues. The residue screening has been treated only as complementary information, rather than a central objective of the study.

Nutritional comparison and experimental fairness: From a nutritional standpoint, the diets provided to the animals were not balanced equally, clearly favoring the diet with tomato by-product silage. This compromises the validity of the comparison and biases the results obtained.

Response: The diets were formulated to be isoenergetic, meeting the requirements for total digestible nutrients equally, while crude protein levels remained close between treatments. It is worth noting that protein content was slightly higher in the control group, which rules out any bias in favor of the silage. The level of concentrate in the control diet was deliberately limited to maintain a practical condition consistent with real production systems, without compromising the validity of the comparison. It is also important to emphasize that diet formulation represents a theoretical expectation, and variations in the actual weight gain observed are inherent to animal feeding experiments.

Note: Detailed comments are provided in the attached file, as the submitted manuscript version does not include line numbering. In summary, the manuscript requires fundamental revisions in methodology, analysis, consistency of information, and alignment with the journal’s scope. It is recommended that the authors address all the points raised before resubmission.

Response: We thank the reviewer for the thorough assessment and the annotated PDF. We reviewed every comment point by point and revised the manuscript accordingly. In brief, we expanded the Materials and Methods to improve reproducibility (including citations for the water-intake procedure), harmonized units (e.g., organic acids in g/kg DM), corrected inconsistencies, clarified the rationale for diet formulation and comparison, and reframed pesticide-residue screening as complementary (removed from the title). We also streamlined the Introduction and Conclusion to better align with the journal’s scope, updated tables/figures, and ensured consistency across text and references. We are grateful for the reviewer’s contributions, which have substantially improved the manuscript.

Author Response File: Author Response.doc

Reviewer 2 Report

Comments and Suggestions for Authors

This is an important study with significant, albeit perhaps not unexpected, results.
Ideally, studies of this type would be limited to farms with access to tomato waste.
It would also be useful to provide an estimate of the number of hours invested in each treatment. Knowing the energy cost of each treatment would allow for a more general assessment of the alternative model's sustainability.
Similarly, providing an estimate of the cost of each treatment would indicate the feasibility of using PMR.

Author Response

Tomato residue silage as a sustainable feed for lambs with implications for performance, water use and meat quality

Manuscript sustainability-3834143

REVIEWER 2:

This is an important study with significant, albeit perhaps not unexpected, results. Ideally, studies of this type would be limited to farms with access to tomato waste. It would also be useful to provide an estimate of the number of hours invested in each treatment. Knowing the energy cost of each treatment would allow for a more general assessment of the alternative model sustainability. Similarly, providing an estimate of the cost of each treatment would indicate the feasibility of using PMR.

Response: We appreciate this comment. The study was conducted in an experimental sector, so energy estimates were limited to transport and compaction. Feeding costs per unit of weight gain were calculated and included as a first indication of feasibility. We acknowledge that broader farm-scale assessments of energy and labor are needed and mention this in the discussion.

Reviewer 3 Report

Comments and Suggestions for Authors

I believe this paper contains valuable information for the utilization of local feed resources.

The experimental methods are based on real-world breeding environments, and the content is considered to have broad applicability.

I think the paper can be published with minor revisions.

Taking into account the comments of other reviewers, I have determined that the paper is suitable for publication following minor revisions.

For details regarding my review comments, please refer to my full review feedback document.

Thank you.

Comments for author File: Comments.pdf

Author Response

REVIEWER 3:

I believe this paper contains valuable information for the utilization of local feed

resources. The experimental methods are based on real-world breeding environments, and the content is considered to have broad applicability. I think the paper can be published with minor revisions. Taking into account the comments of other reviewers, I have determined that the paper is suitable for publication following minor revisions. For details regarding my review comments, please refer to my full review feedback document. Thank you.

“Are the research design, questions, hypotheses and methods clearly stated?” Can be improved

Response: We appreciate this question. The research design, objectives, and methods were already described in detail, and we have now revised the text to make them more explicit and easier to follow.

Materials and methods

P2L90 mixed pasture of Buffel grass (Cenchrus ciliaris) and Urochloa (Urochloa mocambisensis) in estimated proportions of 30% and 70%, respectively. Was the ratio of the two types of grass measured by fresh matter weight or dry matter weight? Or is it a judgment based on visual estimation? Also, can I assume that the nutritional intake levels and health status of the ewes tested were equivalent?

Response: We clarified in the Materials and Methods section that the proportion of Buffel grass (Cenchrus ciliaris) and Urochloa (Urochloa mocambisensis) was estimated visually based on fresh matter. We also stated that all ewes were managed under equivalent nutritional intake conditions and maintained similar health status throughout the trial.

Could the decrease in the "control group" be due to the amount of concentrate fed? Could it be due to a decrease in starch? Also, were there any signs of acidosis observed in the test animals?

Response: The reduced pasture intake in the control group may also have been influenced by the higher relative proportion of concentrate in their diet, which could have limited forage consumption. However, no clinical signs of acidosis were observed, indicating that dietary starch levels were not excessive.

Reviewer 4 Report

Comments and Suggestions for Authors

Strengths of the paper include the novelty of linking animal performance, water intake dynamics, and food safety aspects (pesticide residues) within one study, as well as the clear sustainability implications. However, the manuscript has several weaknesses: the small sample size (n = 18), limited detail in some methodological descriptions, lack of deeper mechanistic discussion, and a few inconsistencies in data interpretation and reporting. Additionally, the discussion could be strengthened by integrating more comparisons with previous studies.

Abstract

The abstract is informative but slightly long. Consider shortening by focusing on the most critical findings (performance improvement, water intake reduction from drinkers, absence of residues).

Clarify that only chlorothalonil was tested in meat samples, while multiple compounds were screened in silage.

Report the exact numerical improvement in weight gain and reduction in direct water consumption for greater impact.

Introduction

The introduction is well-structured but could better emphasize the knowledge gap—specifically, that no studies have simultaneously examined performance, water dynamics, and pesticide transfer.

References on pesticide residue transfer to animal tissues could be expanded, particularly for ruminants, to strengthen the rationale for including this parameter.

Some references are dated (e.g., early 2000s for lignin digestion). Consider including more recent studies to ensure the background is up to date.

Materials and Methods

The sample size of 18 animals (n = 9 per treatment) is quite small for performance trials. Please justify the statistical power and limitations.

Clarify why only chlorothalonil was tested in meat rather than all pesticides tested in silage. Was this due to cost, regulations, or toxicological relevance?

More details are needed on the randomization process to ensure unbiased allocation.

Describe the chemical composition of tomato residue before ensiling to provide baseline context.

The description of pasture availability and quality is adequate, but a figure or table showing changes across the trial would improve clarity.

Indicate whether animals had ad libitum access to silage or whether intake was restricted.

In the water intake method, the use of buckets to measure evaporation is clever, but the number of replicates (n = 3) seems limited. Provide justification.

The pesticide residue detection limits (10–50 µg/kg) should be compared with regulatory maximum residue limits (MRLs) to contextualize the safety assessment.

Results

The performance results are clearly presented, but the absolute differences in weight gain (e.g., 213 g vs. 139 g/day) could be highlighted in the text for readability.

The carcass results indicate significant differences in weights but not in yields. This could be better explained—e.g., were heavier carcasses simply proportional to live weight?

The finding of increased cooking loss in meat is interesting but under-discussed. Was this linked to higher moisture content in tissues? Additional data (e.g., proximate analysis of meat) would strengthen this point.

Figures and tables are generally clear, but Figure 1 (water intake) could benefit from presenting both absolute and relative contributions (feed vs. drinker).

Discussion

The discussion interprets results logically but sometimes repeats them. Consider reducing redundancy and focusing on mechanistic explanations (e.g., how silage moisture reduced drinking water intake, possible microbial pathways of pesticide degradation).

The sustainability implications are strong, but the discussion could connect more explicitly with circular economy principles and practical adoption challenges (e.g., seasonal availability, transportation costs of residues).

Author Response

REVIEWER 4:

This manuscript investigates the use of partial mixed tomato residue (PMR) silage in lamb diets and its effects on productive performance, water intake, and pesticide residues in silage and meat. The study addresses an important topic in sustainable livestock production, particularly relevant for semi-arid regions. The experimental design is generally sound, and the results support the potential of tomato agro-industrial residues as a sustainable feed alternative. Strengths of the paper include the novelty of linking animal performance, water intake dynamics, and food safety aspects (pesticide residues) within one study, as well as the clear sustainability implications. However, the manuscript has several weaknesses: the small sample size (n = 18), limited detail in some methodological descriptions, lack of deeper mechanistic discussion, and a few inconsistencies in data interpretation and reporting. Additionally, the discussion could be strengthened by integrating more comparisons with previous studies.

Response: We thank the reviewer for the constructive feedback. We will improve the manuscript by clarifying methodological details, justifying the sample size, expanding the discussion with more mechanistic interpretation and comparisons, and correcting inconsistencies in data presentation.

Abstract

The abstract is informative but slightly long. Consider shortening by focusing on the most critical findings (performance improvement, water intake reduction from drinkers, absence of residues).

Response: I corrected.

Clarify that only chlorothalonil was tested in meat samples, while multiple compounds were screened in silage.

Response: I corrected.

Report the exact numerical improvement in weight gain and reduction in direct

water consumption for greater impact.

Response: I corrected.

Introduction

The introduction is well-structured but could better emphasize the knowledge gap—specifically, that no studies have simultaneously examined performance, water dynamics, and pesticide transfer.

Response: I corrected.

References on pesticide residue transfer to animal tissues could be expanded, particularly for ruminants, to strengthen the rationale for including this parameter.

Response: We improved this section

Some references are dated (e.g., early 2000s for lignin digestion). Consider including more recent studies to ensure the background is up to date.

Response: We included several recent references.

Materials and Methods

The sample size of 18 animals (n = 9 per treatment) is quite small for performance trials. Please justify the statistical power and limitations.

Response: The initial design included 20 animals (10 per treatment), but two were excluded after pregnancy detection, resulting in nine per treatment. This sample size is within the range commonly reported in sheep nutrition and performance studies (typically 8–12 animals per treatment), and aligns with CEUA (Ethics Committee on Animal Use) recommendations to avoid unnecessary animal use. Although smaller than large-scale production trials, the number was statistically adequate to detect significant differences in intake and weight gain, supporting the validity of our conclusions.

Clarify why only chlorothalonil was tested in meat rather than all pesticides tested in silage. Was this due to cost, regulations, or toxicological relevance?

Response: Only chlorothalonil was tested in meat samples because of its toxicological relevance, as it is classified as a potential human carcinogen. While cost was also a limiting factor, chlorothalonil was prioritized given its widespread use in tomato production and higher public health concern compared to the other compounds. We have clarified in the manuscript that only chlorothalonil was analyzed in meat samples due to its toxicological relevance, as it is considered a potential human carcinogen.

More details are needed on the randomization process to ensure unbiased allocation.

Response: I corrected.

Describe the chemical composition of tomato residue before ensiling to provide baseline context.

Response: I added.

The description of pasture availability and quality is adequate, but a figure or table showing changes across the trial would improve clarity.

Response: In the revised version, we excluded the previous table that only presented mean values and replaced it with a figure showing the changes in pasture composition across the experimental period, which improves clarity.

Indicate whether animals had ad libitum access to silage or whether intake was restricted.

Response: I added.

In the water intake method, the use of buckets to measure evaporation is clever, but the number of replicates (n = 3) seems limited. Provide justification.

Response: We appreciate the reviewer’s observation. We have now clarified in the Materials and Methods that the experimental shed presented homogeneous and stable microclimatic conditions, which justified the use of three buckets as representative replicates to estimate evaporation. This information has been added to the text.

The pesticide residue detection limits (10–50 µg/kg) should be compared with regulatory maximum residue limits (MRLs) to contextualize the safety assessment.

Response: I added. Thank you.

Results

The performance results are clearly presented, but the absolute differences in weight gain (e.g., 213 g vs. 139 g/day) could be highlighted in the text for readability.

Response: I added.

The carcass results indicate significant differences in weights but not in yields. This could be better explained—e.g., were heavier carcasses simply proportional to live weight?

Response: We improved the section by clarifying that the higher carcass weights in the PMR group were directly related to their greater final body weight, while carcass yield and finish traits remained similar between treatments.

The finding of increased cooking loss in meat is interesting but under- discussed. Was this linked to higher moisture content in tissues? Additional data(e.g., proximate analysis of meat) would strengthen this point.

Response: I added.

Figures and tables are generally clear, but Figure 1 (water intake) could benefit from presenting both absolute and relative contributions (feed vs. drinker).

Response: We have addressed this point by adding the percentage differences to the results text, including the corresponding P-values for clarity

Discussion

Response: We revised the discussion by removing redundancies and enriching the text, as suggested.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Author

I appreciate the authors’ effort in addressing the previous comments and significantly improving the manuscript. The overall quality has increased considerably, and the text is now clearer and easier to understand. However, there are still several issues that need to be addressed and some points that require clarification:

1 Standardization of units and figure formatting:

The way units are expressed is still not fully standardized. The y-axes of the figures use formats such as g/kg and kg/day instead of g·kg⁻¹ and kg·day⁻¹. Similar inconsistencies also appear throughout the text and discussion. A thorough and careful revision is recommended to ensure consistent unit expression throughout the manuscript. The font used in the figures should also be standardized to match the main text.

2 Common names of forage species:

The authors presented the common name of Buffel grass but only the genus name of the second grass. It is recommended to include the common names of both species for consistency.

3 Figure 1:

The unit used on the y-axis is unclear. It would be clearer to express it only as g·kg⁻¹ and specify in the legend whether the values are on a dry matter or fresh matter basis. Additionally, the title and legend should be presented as a single paragraph.

4 Experimental description and diets:

The term “surface silo” is unclear. Please explain what it means and justify why the silage was kept under fermentation for eight months.

The description of the diets is confusing. A table should be added showing the ingredient proportions and the chemical composition of each diet. Table 1, currently presented in the Results section, is incorrect, as it omits the pasture fraction of the diet.

According to the text, the control diet was not offered ad libitum, whereas the tomato silage diet was. This creates an imbalance when comparing intake and weight gain, as the restricted intake of the control diet could directly affect performance results.

Figure 1 shows variation in the nutrient contents of the pasture. Considering that pasture was the main component of the control diet and the concentrate remained constant, how can the authors claim that the diets were isoenergetic? This appears to be one of the weakest aspects of the study. It is recommended to describe in the Materials and Methods section the diets that the animals actually consumed, rather than the planned ones. Alternatively, a table comparing the planned and actual diets could be included. This would help explain why a diet formulated to achieve 200 g/day of average daily gain resulted in only 138 g/day.

In the Materials and Methods, it is stated that pasture accounted for 10.9% of the “PMR” diet, but the intake table shows a much higher value. This inconsistency needs clarification.

5 Butyric acid:

Is a value of 8.9 g/kg (0.89%) of butyric acid in DM considered good for silage? Please provide a reference supporting this statement and double-check the calculations.

6 Conclusion:

The conclusion should be more concise and focus only on the main findings of the study. At the end, the authors may include brief suggestions for future research.

Best regards

Author Response

Tomato residue silage as a sustainable feed for lambs with implications for performance, water use and meat quality

Response: We appreciate the reviewer’s careful attention to the manuscript.

1 Standardization of units and figure formatting:

Response: I correct

2 Common names of forage species:

The authors presented the common name of Buffel grass but only the genus name of the second grass. It is recommended to include the common names of both species for consistency.

Response: I correct

3 Figure 1:

Response: I correct

4 Experimental description and diets:

The term “surface silo” is unclear. Please explain what it means and justify why the silage was kept under fermentation for eight months.

Response: We improved

In the Materials and Methods, it is stated that pasture accounted for 10.9% of the “PMR” diet, but the intake table shows a much higher value. This inconsistency needs clarification.

Response: We appreciate the reviewer’s intervention, which has significantly improved the clarity and overall quality of the manuscript. We have added a note in the footnote of Table 1 to clarify that pasture was excluded from this table, as it only presents the ingredients and chemical composition of the concentrate and PMR silage. In addition, we revised the text to specify that in the control group the pasture fraction was offered ad libitum, while concentrate was restricted to 1.8% of body weight. Regarding the issue of isoenergetic diets, we improved the text in the Materials and Methods by explicitly indicating that diets were planned to be isoenergetic. To further address this point, we also included a new table (Table 3) comparing the planned diets with those actually consumed, which clarifies the apparent inconsistency and explains why the diet formulated for an average daily gain of 200 g/day resulted in 138 g/day in the control group. We believe these changes satisfactorily address the reviewer’s concerns and make the description of diets and their interpretation clearer and more robust.

5 Butyric acid:

Is a value of 8.9 g/kg (0.89%) of butyric acid in DM considered good for silage? Please provide a reference supporting this statement and double-check the calculations.

Response: Thank you for pointing this out. We rechecked the calculation and confirm that the butyric acid concentration is 8.87 g·kg⁻¹ DM (0.887% DM), derived from 3.05 g·kg⁻¹ as-fed and a silage dry matter of 343.8 g·kg⁻¹. Regarding interpretation, this value is not considered good. According to established guidelines, well-preserved silages typically contain little or no detectable butyric acid, with recommended thresholds <0.5% DM (≈ <5 g·kg⁻¹ DM). Concentrations between 0.5–1.0% DM are regarded as a warning range for clostridial activity, while >1.0% DM is usually associated with severely deteriorated silages. Our result (0.887% DM) therefore falls in the warning range, indicating clostridial fermentation, but remains below the threshold for severe deterioration. We have clarified this limitation in the revised text and included the effect of the extended fermentation time (eight months) as a possible factor contributing to this butyric acid level.

6 Conclusion:

The conclusion should be more concise and focus only on the main findings of the study. At the end, the authors may include brief suggestions for future research.

Response: We improved

Reviewer 4 Report

Comments and Suggestions for Authors

It can be accepted.

Author Response

Thank you very much for your positive evaluation and recommendation.

Kind regards,