Valorization of Organic Food Surpluses and Brewer’s Spent Grains into Organic Insect Protein for Replacing Soybean in Post-Weaning Piglets

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is focused on the partial replacement of soy protein by protein from an insect (Black soldier fly) grown from organic plant residues, in post-weaning piglets. The paper includes a good introduction, clear methodology, and, in general, well discussed and results section. From the reading of the work, I have a big question related to the main objective of the work. Do the authors expect that the piglets' growth was different because of the substitution from 15 to 35 % of soy protein? If the feed formulations were equal in terms of protein and certain amino acids, was it possible to have remarkable differences in the growth of piglets according to the formulation?

Line 236: could you check the Piglet feed MScor column values? I am not sure if the values of the column are calculated in dry matter; should they not be higher than the values of the piglet feed as feed?

 

Line 261: n is not 18? 6 pens by 3 piglets each?

Figure 1: Please use different colors for the 2 and 4 formulations. It is hard to see

 

Figure 2: Please consider to better explaining the difference between figure1 and 2. The same with colors for 2 and 4 formulations

In the discussion, a better explanation about differences between R3 formulation and the others should be appreciated. Why 25% replacement offer a slightly worse result compared to 15 or 35 % of substitution? Or were the differences so minimal that they were not worth discussing?

Author Response

Reviewer 1

Question: The paper is focused on the partial replacement of soy protein by protein from an insect (Black soldier fly) grown from organic plant residues, in post-weaning piglets. The paper includes a good introduction, clear methodology, and, in general, well discussed and results section. From the reading of the work, I have a big question related to the main objective of the work. Do the authors expect that the piglets' growth was different because of the substitution from 15 to 35 % of soy protein? If the feed formulations were equal in terms of protein and certain amino acids, was it possible to have remarkable differences in the growth of piglets according to the formulation?

Response: We thank the reviewer for this relevant comment. Although the experimental diets were formulated to be isoenergetic and isonitrogenous, with similar estimated standardized ileal digestible (SID) levels for four essential amino acids (lysine, methionine, threonine, and tryptophan), differences in animal performance could still reasonably be expected due to the intrinsic differences between the protein sources.

Indeed, the study compared conventional plant based protein sources with an animal derived protein source (defatted BSF meal), which differ in several nutritional and physicochemical characteristics that may influence nutrient utilization and animal performance. For example, EU regulations require different processing and heat treatment conditions for insect meals and plant protein ingredients, which may differently affect amino acid availability, particularly reactive lysine. In addition, BSF meal contains higher mineral and calcium levels, potentially modifying dietary buffering capacity and digestive conditions. The presence of chitin may also affect nutrient digestibility and gut function.

Furthermore, diet formulation was standardized only for four essential amino acids, whereas the digestibility and balance of the remaining essential and non essential amino acids were not specifically evaluated. Consequently, differences in the actual bioavailability, digestion kinetics, and metabolic utilization of amino acids between protein sources may still occur and potentially influence piglet growth performance.

 

Question: Line 236: could you check the Piglet feed MScor column values? I am not sure if the values of the column are calculated in dry matter; should they not be higher than the values of the piglet feed as feed?

Response: We are very grateful to the reviewer for pointing out this error. We have corrected this typo throughout the column and checked each table.

 

 

Question: Line 261: n is not 18? 6 pens by 3 piglets each?

Response: We would like to thank the reviewer once again for pointing out this typing error. The number 24 has been replaced with 18.

 

Question: Figure 1: Please use different colors for the 2 and 4 formulations. It is hard to see

Response: Thank you for your feedback. We have updated the color scheme of the figure to make it easier to read.

 

 

Question: Figure 2: Please consider to better explaining the difference between figure1 and 2. The same with colors for 2 and 4 formulations

Response: For each figure, we have included a sentence to help distinguish between weekly gain (flow) and body weight (accumulation):

L348 “Although weekly gain tended to be lower for R3 on average across the study period, week-specific contrasts were not significant after Tukey adjustment. This likely reflects the relatively high week-to-week variability in gain measurements and the fact that the weekly-gain model estimated average diet effects across weeks without including Diet × Week interactions. In contrast, the body-weight trajectory model evaluated cumulative growth over time and allowed diet-specific slopes, such that relatively small but repeated differences in weekly gain progressively accumulated and became detectable at later weeks.”

L377 “Because body weight represents the cumulative result of successive weekly gains, relatively small differences in gain efficiency between diets became progressively amplified over time, leading to divergence in predicted body-weight trajectories.”

 

Question: In the discussion, a better explanation about differences between R3 formulation and the others should be appreciated. Why 25% replacement offer a slightly worse result compared to 15 or 35 % of substitution? Or were the differences so minimal that they were not worth discussing?

Response: We thank the reviewer for this relevant observation. Although the R3 diet (25% replacement) showed slightly lower performance values than the R2 (15%) and R4 (35%) diets for some parameters, these differences were small and not statistically significant between the higher inclusion levels. Consequently, no clear dose-dependent response pattern could be identified. Given the absence of significant differences between R3 and R4, we considered that further biological interpretation of the slightly lower R3 values would be speculative and potentially misleading. We have nevertheless clarified this point in the Discussion section to emphasize that the observed variations among higher BSF inclusion levels remained limited and did not support the identification of a specific threshold effect at 25% substitution:

L440: “Although the 25% inclusion rate numerically showed lower values than the 35% inclusion rate for some parameters, these differences were not statistically significant and therefore cannot be interpreted as evidence of a specific underperformance at the intermediate inclusion level.”

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript entitled Valorization of Organic Food Surpluses and Brewer’s Spent Grains into Organic Insect Protein for Replacing Soybean in Post-Weaning Piglets, trying to estimate the conversion of agro-industrial co-products and unsold organic plant-based residues into black soldier fly proteins and its performance in organic post-weaning piglet diets. This study is very interesting and of great practical values, which provides a detailed economic estimation of BSF resource utilization. Some minor revisions are encouraged as follows.

1. Section 2.1: The description of BSFL rearing is hard to follow, especially the part of substrate composition. Please reorganize this section in an easier and clearer way.
2. Line 135: As mentioned here, the harvested biomass of BSFL is 555 kg, and what isthe bioconversion rate? Does this rate reach an average leve of BSFL bioconversion technique reported in other studies?
3. The author listed a large amount of data on amino acids, however, the analysis of these data is not thorough enough. It is strongly recommended to add the correlation analysis between amino acid content and piglet weight.
4. For the figures, present form is hard to distinguish the differences between each other. Significance analysis between different experimental groups should be added.
5. Line 305: Why P0=€1039 /t? How to reach this value? I think it has been presented in section 2.7, but it is still appreciated to express it in an easily understandable way for the readers.
6. In general, I think this work provided meaningful results. However, the presentation format of these data (tables and figures) is too simple to describe such a long process flow and economic accounting. A table of contents graphic (TOC) could be a good solution for readers to better understand the main idea of this manuscript.

Author Response

Reviewer 2

Question: Section 2.1: The description of BSFL rearing is hard to follow, especially the part of substrate composition. Please reorganize this section in an easier and clearer way. Line 135: As mentioned here, the harvested biomass of BSFL is 555 kg, and what is the bioconversion rate? Does this rate reach an average leve of BSFL bioconversion technique reported in other studies?

Response: We thank the reviewer for these comments. Section 2.1 has been reorganized to improve clarity and readability, particularly regarding substrate composition, processing, and larval rearing conditions.

We also clarified the production yield obtained during the rearing process. Based on the 4730 kg of collected fresh organic substrate and the 555 kg of fresh larval biomass harvested, the approximate fresh biomass conversion rate was 11.7%. However, direct comparison with values reported in the literature should be made cautiously, as bioconversion efficiency strongly depends on substrate composition, moisture content, larval density, rearing duration, and the calculation method used (fresh matter vs dry matter basis).

 

Question: The author listed a large amount of data on amino acids, however, the analysis of these data is not thorough enough. It is strongly recommended to add the correlation analysis between amino acid content and piglet weight.

Response: We thank the reviewer for this suggestion. The detailed description of amino acid analyses in the Materials and Methods section reflects the different hydrolysis procedures required for accurate quantification of individual amino acids. However, the amino acid composition was primarily determined to formulate nutritionally equivalent diets and subsequently verified analytically as a quality control measure. The objective of the study was not to investigate the effect of different amino acid profiles on piglet growth performance, as the diets were intentionally formulated to provide comparable protein and amino acid levels. Therefore, amino acid composition was considered a controlled formulation parameter rather than an experimental explanatory variable. Under these conditions, performing correlation analyses between amino acid content and piglet body weight would not be biologically meaningful, since only minimal variation in amino acid concentrations existed among the experimental diets.

 

Question: For the figures, present form is hard to distinguish the differences between each other. Significance analysis between different experimental groups should be added.

Response: Thank you for your feedback. We have updated the figure with new colors to make it easier to read. We have intentionally removed the significance symbols from the figures because they clutter the figure and actually make it harder to read.

 

Question: Line 305: Why P0=€1039 /t? How to reach this value? I think it has been presented in section 2.7, but it is still appreciated to express it in an easily understandable way for the readers.

Response: We thank the reviewer for this comment. We clarified in Section 2.7 that the values of (P_0) and (P_e) correspond to the actual supplier prices of the protein and energy cores during the experimental period, excluding VAT:

L309: “Diets consisted of an energy core (price (P_e = €529)·t⁻¹, excluding value-added tax (VAT); share (f_e = 0.812)) and a protein core (control price (P_0 = €1039)·t⁻¹, excluding VAT; share (f_p = 0.188)). These prices corresponded to the actual feed prices charged by suppliers during the experimental period.”

 

Question: In general, I think this work provided meaningful results. However, the presentation format of these data (tables and figures) is too simple to describe such a long process flow and economic accounting. A table of contents graphic (TOC) could be a good solution for readers to better understand the main idea of this manuscript.

Response: We thank the reviewer for this suggestion. A graphical abstract summarizing the experimental design and the main outcomes of the study was already included in the submitted manuscript. We believe that this figure provides an overview of the dietary treatments and their effects on piglet performance.