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Based on the reviewers' overall evaluations, the article has been accepted for publication. I congratulate the authors.
[# PeerJ Staff Note - this decision was reviewed and approved by Jennifer Vonk, a PeerJ Section Editor covering this Section #]
The revised version shows a clear improvement in structure, language quality, and logical flow. The Abstract has been shortened and is now more concise and readable. Repetitive statements in the Introduction have been removed, and the narrative is more streamlined. The manuscript is generally well written and uses appropriate scientific terminology.
Figures and tables have been reorganized according to the journal’s formatting requirements, and the authors have added the requested schematic figure illustrating the regulatory mechanisms of rumen development. Citations are appropriate and up-to-date. The manuscript now reads more clearly as a narrative review, which aligns with the changes requested by the reviewers.
Minor English polishing would still improve readability, but this does not impede scientific comprehension.
Overall: Basic reporting is acceptable after revision.
The main methodological issue raised in the previous round concerned the inconsistency between the manuscript’s description (which resembled a systematic review) and the absence of PRISMA elements. The authors have resolved this by reclassifying the manuscript as a narrative review and removing statements implying systematic review methodology. This now aligns the study design with the evidence synthesis approach used.
The Methods section adequately explains the search strategy and scope but does not attempt to follow systematic-review protocols, which is now acceptable given the clarified manuscript type.
The conceptual organization—including genetics, nutrition, microbiota, and physiological mechanisms—is logical and reflects the aim of presenting a broad overview of rumen development in young ruminants.
Overall: The study design is now consistent with a narrative review and acceptable.
The authors have improved the discussion by clarifying conflicting research (e.g., prenatal microbial colonization) and by strengthening conceptual links between different regulatory factors. The newly added schematic diagram helps visualize the GH/IGF and metabolic pathways involved in rumen development.
The findings remain descriptive in nature, which is appropriate for a narrative review. Although the article still lacks a deeply integrated conceptual model, the revised text now provides better synthesis than the initial submission.
The conclusions are balanced, supported by the reviewed literature, and avoid overstated claims.
Overall: The scientific validity is acceptable for a narrative review.
The addition of the mechanism figure substantially enhances the manuscript and responds well to reviewer feedback.
The removal of redundant text has significantly improved readability.
Discussion and “Summary and Prospect” sections are now more focused and appropriately concise.
The manuscript could still benefit from minor language refinement, but no major issues remain.
Recommendation: Accept after minor polishing.
While the article has improved significantly since the initial revision, several important issues remain unresolved. According to reviewer comments, the article still lacks a true PRISMA flowchart and does not meet the criteria for a systematic review. The Discussion is largely descriptive and lacks a clear conceptual synthesis. Furthermore, authors should shorten the Abstract, remove unnecessary statements, and provide at least one integrated schematic figure summarizing the factors and mechanisms. Therefore, a comprehensive revision is required before further consideration.
Strengths:
The article is well organized, written in clear academic English, and technically adequate.
Current sources (especially for the 2023–2025 period) are impressively covered.
The literature review is broad and multifaceted: genetic, hormonal, environmental, and nutritional factors are addressed together.
Weaknesses / Suggestions for Improvement:
The Abstract section is too long and full of technical terms; it should explain the original contribution of the topic more clearly to the reader.
Some statements in the text (“this review systematically summarizes...”) imply that the review is systematic—but the methodology section lacks sufficient evidence (e.g., a PRISMA diagram) to support this claim.
Although the references are correctly cited, the accessibility or numbering of tables and figures is unclear.
Some sentences (especially in the Introduction section) repeat the same concepts; for example, the phrase “rumen development is regulated by genetics, nutrition, and environment” is repeated several times.
Strengths:
The literature review was based on PubMed and Web of Science databases, with the search strategy and keywords clearly specified.
The screening process, which narrowed down 3,728 articles to 102 publications, was reported quantitatively — demonstrating methodological rigor.
Weaknesses / Recommendations for Improvement:
The authors defined a systematic review process but did not comply with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses).
Inclusion/exclusion criteria, quality assessment method, and double-blind screening procedure were not specified.
A PRISMA flow diagram or PRISMA 2020 checklist is not provided.
If the aim is to conduct a systematic review, this omission constitutes a major methodological weakness.
Otherwise, the authors should reclassify this article as a “narrative review.”
Reviewer Comment (in the form of a suggestion):
The manuscript describes a search process resembling a systematic review but lacks PRISMA compliance. To ensure methodological transparency, the authors should either (1) provide a PRISMA 2020 flowchart and checklist, or (2) clarify that this is a narrative review synthesizing recent advances. Without this clarification, the review type remains ambiguous.
Strengths:
Romanian development and regulatory mechanisms (GH/IGF axis, RAP1A–PI3K/AKT pathway) are summarized in accordance with the literature.
Numerous references, particularly from the 2024–2025 period, demonstrate strong timeliness.
The study integrates different biological levels (molecular, cellular, physiological).
Weaknesses / Suggestions for Improvement:
The findings are limited to a literature review; the “synthesis” aspect is weak. The article merely summarizes the literature but does not present a new conceptual model or meta-analytic conclusions.
The “Summary and Prospect” section is unnecessarily long and repetitive; it should be shorter, clearer, and more focused.
A critical comparison of the findings is lacking—for example, conflicting data (such as whether microbial colonization begins before or after birth) should be discussed.
The review comprehensively summarizes the effects of genetic, nutritional, and microbial interactions on rumen development.
Although the scientific content is strong, the type of review and its methodological framework are unclear.
The scientific impact would be enhanced by adding visual materials (e.g., a diagram showing rumen development stages or GH/IGF – PI3K/AKT interactions).
The text is well edited, but shortening some sentences would improve readability.
The article addresses an important topic, but in its current form, it remains more of a literature summary. Authors should systematize their literature selection, increase analytical depth, correct overly specific statements, and enhance critical discussion. They are also expected to clearly differentiate themselves from similar recent reviews. Please revise the manuscript to ensure scientific rigor and clarity for Language and Style.
**PeerJ Staff Note:** Please ensure that all review and editorial comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
**Language Note:** The review process has identified that the English language must be improved. PeerJ can provide language editing services - please contact us at [email protected] for pricing (be sure to provide your manuscript number and title). Alternatively, you should make your own arrangements to improve the language quality and provide details in your response letter. – PeerJ Staff
This manuscript on rumen development in ruminant production holds significant practical value. It systematically examines influencing factors and underlying regulatory mechanisms, thereby providing guidance for future research and a theoretical foundation for improving farming efficiency. The article offers a comprehensive review of multiple aspects, including anatomical and physiological development, as well as key factors such as genetics and nutrition. Furthermore, it draws extensively on international literature, establishing a robust theoretical basis for the field.
Some suggestions：
1. The literature search strategy is described too briefly. A PRISMA flow chart should be included to illustrate the process of literature screening, thereby improving the transparency of the methodology.
2. Genes associated with rumen development play a critical role; however, their functions are described in an overly generalized manner in the text. It is recommended to systematically summarize the key genes involved in rumen development and their specific functional roles, ideally presented in a tabular format for improved clarity and conciseness.
Line 1: The phrase "closely linked to" appears somewhat colloquial; replacing it with "strongly correlated with" better aligns with the rigor of academic expression.
Lines 50-52: Some long sentences could be divided to enhance readability. For instance:
Original: " The early-life stage constitutes a pivotal period for rumen development in ruminants, with its developmental extent directly impacting the production performance of animals in adulthood."
Revised version: "The early-life stage is pivotal for rumen development in ruminants. Its developmental extent directly impacts the production performance of adult animals."
Lines 211-212: In the sentence "Maternal nutritional levels can influence fetal nutrient availability and can have long-term effects on offspring development," the second "can" can be omitted.
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This review article summarizes factors that influence the rumen development in young ruminant species. It is well written for the most part, but aspects are often generalized, and sometimes it is not clear which ruminant species is addressed. In addition, different husbandry and feeding conditions probably influence the rumen development in more complex ways than is often claimed.
Some studies are also not cited correctly, and important findings from other studies are not included. Additionally, a very similar review has recently been published (Pokhrel and Jiang, 2024; https://doi.org/10.3390/biology13040269).
I have listed several concerns in the specific comments below, hoping that they can help the authors improve their review article.
As mentioned above, some studies are not cited correctly, and important findings from other studies are not included.
Additionally, a very similar review has recently been published (Pokhrel and Jiang, 2024; https://doi.org/10.3390/biology13040269.
The review article ends with a summary and a basic prospect for future research. No specific unresolved questions are addressed.
Specific comments to the Authors
I suggest specifying the keywords. ‘Influencing factors’ and ‘regulatory mechanisms’ are too general.
Line 58: I suggest rephrasing this sentence. Starting with ‘we hope’ does not sound very scientific. E.g., ‘This review is intended for…’ seems more appropriate.
Line 665: Why did you not include “rumen microbiome” or “ruminal microbes”?
Line 69: Please include information on the number of studies found and included.
Line 71: I don´t see why this paragraph is needed. It could be deleted.
Line 72: Digestion and microbial fermentation are not the same. Please check and rephrase.
Lines 84 to 87: these measurements are from one specific study, and the specific numbers, which are probably mean values, are not valid for every cashmere goat. The numbers are much too specific.
Line 89: Again, 156.20 is too specific and will not be valid for every goat. ‘approximately’ seems wrong when given such specific numbers.
Lines 89 to 94: Is this valid for all ruminant species?
Line 99: The development of branches depends on the diet. If ruminants are fed with forages only. The ruminal papillae will most likely not develop branches. Please rephrase.
Line 115: Do species other than ruminants have a rumen? If not, delete ‘of ruminants’.
Line 116: Again, fermentation and digestion are not the same.
Line 117: delete ‘digestive’
Line 118: rephrase to ‘it was long been assumed that…’
Line 132 and following: There have been several reviews on the ruminal microbiome, e.g., Moraïs, S., & Mizrahi, I. (2019). Islands in the stream: from individual to communal fiber degradation in the rumen ecosystem. FEMS microbiology reviews, 43(4), 362-379. These authors also discussed rumen colonization. I suggest referring to this review and adding new insights since 2019.
Line 142: change ‘digesting’ to ‘degrading’
Line 155: What do you mean by ‘carbon substrates’? Is acetate not a carbon substrate? I think ‘carbon substrates’ could be anything based on carbon; accordingly, only a very small fraction of carbon substrates could be used by methanogens. Please be more specific.
Line 161: Please include a younger study.
Line 166: Is that really so? Please add a reference supporting that anaerobic fungi contribute more to fibre degradation than bacteria.
Line 202: only between breeds or also between species?
Line 206: What is a strong roughage tolerance? Of course, ruminants have evolved to digest roughage; it would be strange if they could not tolerate roughage.
Line 207: How is the abundance of unclassified Veillonellaceae related to the genetic basis?
Line 215: and species?
The whole section about Genetic factors seems to be too superficial. The authors speak of effects and influences but don´t go into detail.
Line 242 and following: What is “lactation quality”? Do you mean milk production and milk quality?
Line 250: exactly 10.99%? This is too specific, especially when considering different breeds of sheep.
Line 255:Whichh plant plant-derived additives? This statement is too general.
Line 266: In most dairy systems, after colostrum provision, the offspring are no longer fed with the maternal milk but with tank milk or milk replacer. Accordingly, you have to consider different production systems.
Line 280: Please provide a reference for butyrate being most effective.
Line 280-282: Why is PacÌfico et al., 2022 used as a reference here? I could not find a direct connection.
Line 282/283: What do you mean by “artificial feeding”?
Line 291-293: Is this also related to the duration of supplemental feeding? After which duration of feeding were the measurements conducted?
Line 295: Digestibility of what exactly?
Line 296/297: I assume this depends on the feeding system and the diet. Intensive calf fattening for veal production relies strongly on milk consumption.
Line 297: Weaning of calves at the age of 35 days is very early and cannot, per se, be recommended for several reasons. In the study that you are citing, calves were weaned at the age of 60 days, and it was the aim to investigate the effects of different carbohydrates in milk replacer and not different times of weaning.
Line 303: What do you mean by “timely weaning”? I consider it even dangerous to recommend early weaning in terms of animal health and welfare.
Line 317 and following: Check the studies by the animal nutrition group of Prof. Zebeli from Vetmeduni Vienna. They have conducted research on high-quality hay feeding in calves and published several papers concerning this topic.
Line 329: What is scientifically balancing?
Line 323: It is strongly debated what to consider an optimal rumen development. A ratio of 50:50 is still a lot of concentrates, and there are many studies showing detrimental effects of concentrate feeding on the ruminal epithelium, which should be included in this review. Risks of excessive concentrate feeding need to be discussed.
Line 349: How can noxious gases like ammonia from the air be detrimental to the rumen tissue?
Line 359/360: There are several studies showing that VFA inhibit GH release, e.g., https://doi.org/10.1006/gcen.2000.7468; https://doi.org/10.3390/ijms141121474
Line 365: Why ketone bodies? The study of Wang et al. (2017) analysed the effects of supplemental isobutyrate, a branched-chain volatile fatty acid, which cannot necessarily be compared to other VFA deriving from carbohydrate fermentation.
Line: 369: Please cite a study showing that VFA stimulates the secretion of EGF. I could not find it in Pokhrel & Jiang (2024).
Lines 371-380: Pokhrel & Jiang, 2024, is a review article. This should be mentioned in the text, and the original studies should be included.
Line 386: Is prostaglandin D2 a microbial metabolite? As far as I know, it is not.
Line 417: Does efficient ruminant production practice include improving animal health? If not per se, I suggest including the health aspect.
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