Amino acid and fiber characterization of multi-species hydroponic sprouts with implications for small herbivore meat-type breeding programs

Introduction

Meat-type rabbit breeding programmes aim to maximise the deposition of lean skeletal muscle while minimising fat accumulation, a goal that demands diets supplying not just adequate total protein but a balanced spectrum of essential amino acids in proportions that match the animal's tissue-synthesis requirements [1] . In contrast to the poultry and swine industries, where amino acid nutrition has been refined over decades through dose-response trials and ideal-protein models, the rabbit sector particularly in sub-Saharan Africa still relies heavily on crude-protein targets rather than amino acid specifications when formulating rations [2,3] . This reliance persists partly because amino acid data for locally available feed ingredients are scarce and partly because synthetic amino acid supplements are expensive or unavailable in rural markets. Hydroponic sprouts have atracted interest as a low-cost feed supplement for rabbits in tropical regions, but nearly all published evaluations report only proximate composition crude protein, crude fibre, ether extract, ash rather than the amino acid detail needed for precision diet formulation [4,5] . A sprout with 22 % CP may contain twice as much lysine as one with 13 % CP, yet if the former is also deficient in methionine, the animal's protein synthesis will be limited by the first-limiting amino acid, and excess nitrogen will be deaminated and excreted at a metabolic cost [6] . Characterising the essential amino acid profiles of diferent sprout species is therefore a prerequisite for designing mixed-species sprouting strategies that exploit amino acid complementarity. Fibre quality is the second dimension that standard CF analysis obscures. The Van Soest detergent system partitions total fibre into neutral detergent fibre (NDF cell wall), acid detergent fibre (ADF cellulose plus lignin), and acid detergent lignin (ADL lignin alone) [7] . For rabbits, whose caecal fermentation relies on a balance between rapidly fermentable fibre and indigestible lignin, these fractions are more informative than CF because they predict both voluntary intake and the eficiency of hind-gut microbial activity [8] .

Yet NDF, ADF, and ADL values for hydroponic sprouts are virtually absent from the literature. This research therefore undertook a comprehensive characterisation of five hydroponic sprout species three cereals (maize, barley, sorghum) and two legumes (cowpea, mung bean) at Ashanti College of Applied Agriculture, Kumasi, Ghana. The objectives were: (a) to quantify the essential amino acid profiles and Van Soest fibre fractions of each sprout species harvested on day 8 under a standardised greenhouse protocol; (b) to map these profiles against NRC amino acid requirements for growing meat-type rabbits; and (c) to identify single-species and blendedsprout options that most closely satisfy both lysine and methionine requirements, with implications for reducing synthetic amino acid use in small herbivore feeding programmes.

Material and Methods

Material and Study Area

The research was conducted at the Animal Nutrition Laboratory and greenhouse facility of Ashanti College of Applied Agriculture, Kumasi, Ghana (6.69°N , 1.62°W , 250ma . 5 . l .) , from March to August 2022. Kumasi has a tropical wet semideciduous climate (Am, Köppen), with mean temperatures of 25-31°mathsfC and two rainy seasons (March-July, September-November). The greenhouse (5×3m , shade-net walls, clear polyethylene roof) maintained 29±3°mathsfC and 75±7 % RH without mechanical cooling. Seeds of maize (var. Obatanpa), barley (imported feedgrade), sorghum (var. Kapaala), cowpea (var. Asontem), and mung bean (var. VC6173B-10) were procured from the Crops Research Institute, Kumasi; germination exceeded 91 % for all lots.

Methods

Seeds were disinfected (1 % NaOCl, 15 min), rinsed, and soaked for 24 h. Pre-germinated seeds were spread at 3.0kgm⁻² on perforated trays (55×40cm) with coir liners and placed on fourtier steel shelving. Irrigation was by hand sprayer 4 × daily. Trays were harvested on day 8 (five replicate trays per species per harvest). Fresh weight was recorded; sub-samples ovendried at 60 °C for 72 h. Proximate analysis followed AOAC (2005). Essential amino acids (lysine, methionine, threonine, leucine, isoleucine, valine, phenylalanine, histidine, tryptophan) were quantified by ion-exchange chromatography at the Noguchi Memorial Institute for Medical Research, Accra. NDF, ADF, and ADL were determined by the Van Soest sequential detergent method using an ANKOM fibre analyser. Data were analysed by one-way ANOVA in R 4.2; means separated by Tukey's HSD (P < 0.05).

Crop Growth Stage Documentation

Germination progression was tracked visually across all five species. Radical emergence occurred within 24-36 h in all species, with maize and mung bean the earliest. By day 3, coleoptiles in the cereals had reached 3-5 cm, while legume hypocotyls measured 2-4 cm. Shoot elongation accelerated between days 4 and 7 in all species, with maize producing the tallest shoots (21.2 cm at day 8) and mung bean the shortest (9.8 cm). Root-mat formation was densest in barley and mung bean, creating cohesive mats that held together when trays were tilted, whereas sorghum root mats were looser and more prone to fragmentation during handling. By day 8, all trays had transitioned from the seed-reserve-dependent phase to early autotrophic growth, though the limited light in the shade-neted greenhouse restricted net photosynthetic carbon gain. Visual mould was absent from all trays during the trial. All five species germinated uniformly and formed harvestable sprout mats by day 8. Cowpea and mung bean sprouts contained markedly higher total essential amino acid concentrations (10.2 and 10.8 % DM, respectively) than the three cereals (6.9-8.4 % DM; P < 0.001). The amino acid data (Table 1) reveal a clear complementarity patern: legume sprouts excel in lysine and threonine, while cereals particularly maize supply more methionine per unit of DM. The pie chart (Figure 1) visualises the amino acid distribution within cowpea sprouts, highlighting lysine's prominence among the essential amino acids. 2) show that sorghum had the highest NDF (42.6 % DM), ADF (26.3 %), and ADL (6.2 %), indicating the most heavily lignified cell walls among the five species. Mung bean ranked lowest on all three fibre measures, consistent with its thin-walled, rapidly elongating hypocotyl tissue. The flowchart (Figure 2) outlines the multi-species characterisation workflow from seed selection through analytical endpoints. The grouped-bar chart (Figure 3) provides a visual comparison of NDF, ADF, and ADL across species, making the sorghum-mung bean contrast especially apparent.

Results

Limitations

Several limitations should be acknowledged. First, this research was a laboratory characterisation trial and did not include a liveanimal feeding component; the nutritional implications for meat-type rabbits are therefore inferred from the amino acid and fibre data rather than demonstrated by growth or carcass measurements. Second, only one harvest day (day 8) was evaluated, so temporal changes in amino acid profiles across the growth cycle remain unknown. Third, tryptophan recovery by ion-exchange chromatography can be incomplete owing to acid hydrolysis destruction; the tryptophan values reported here should be interpreted with caution. Fourth, the mung bean cultivar used (VC6173B-10) is not widely available in Ghanaian markets, and its amino acid profile may difer from locally adapted varieties. Fifth, anti-nutritional factors trypsin inhibitors, phytate, tannins were not assayed; while germination reportedly reduces these compounds by 40-60 %, residual levels could afect in-vivo protein digestibility and amino acid bioavailability. Finally, the cost of amino acid analysis itself is substantial and may limit the replicability of this approach for routine feedquality monitoring on smallholder farms.

Comprehensive Interpretation

The amino acid and fibre data together outline a practical feedformulation strategy for meattype rabbit breeding programmes. Legume sprouts (cowpea, mung bean) supply lysine and threonine at or above NRC requirements but fall short on methionine. Cereal sprouts (maize) provide the best methionine supply but are lysine-deficient. A blended-sprout approach approximately 60 % cereal and 40 % legume on a DM basis would exploit this complementarity, meeting both first-limiting amino acid thresholds without synthetic supplementation. On the fibre side, the low NDF and ADL of mung bean make it the most digestible option, while sorghum's high lignin content argues against its use as a primary sprout species for rabbits. These profiles give breeders and nutritionists a data foundation for designing precision diets that support lean-tissue accretion while keeping feed costs within the reach of smallholder operations.

Discussion

The essential amino acid profiles reported here fill a gap in the hydroponic-feed literature that has practical consequences for rabbit diet formulation. The finding that cowpea sprouts supply 0.74 % lysine on a DM basis above the NRC requirement of 0.65 % for growing rabbits means that a 25 % DM inclusion of cowpea sprouts in a basal diet containing 12-14 % lysinedeficient cereal CP could bring total dietary lysine close to the target without the addition of synthetic L-lysine [1, 6, 14]. This is a meaningful cost saving for Ghanaian smallholders, for whom imported amino acid supplements are often prohibitively expensive. The amino acid complementarity between cereals and legumes observed here mirrors the wellestablished patern in human nutrition, where cereal-legume food combinations (rice and beans, maize and groundnut) provide a more complete amino acid profile than either component alone [9] . In the hydroponic context, the implication is that mixed-species trays or alternating cereal and legume tray schedules could deliver a balanced amino acid intake to rabbits without requiring the producer to purchase separate protein supplements [10,11] . The fibre data deserve separate atention. Sorghum's high ADL (6.2 % DM) signals heavy lignification, which reduces the proportion of cell-wall material available for caecal fermentation and may depress overall DM digestibility [7,8] . Mung bean's ADL of only 3.1 % suggests the most fermentable fibre matrix, consistent with its thin-walled hypocotyl tissue.

For meat-type rabbit diets, where the goal is to maximise nutrient extraction from fibre rather than simply provide bulk, the NDF: ADL ratio is a useful shorthand: mung bean's ratio of 9.6: 1 is more favourable than sorghum's 6.9: 1, indicating a higher proportion of potentially digestible fibre per unit of total cell wall [12,13] . A practical question is whether the amino acid advantages documented here translate into measurable growth or carcass improvements in live-animal trials. The present research did not include a feeding component, so this question remains open. However, the magnitude of the lysine diference between cowpea (0.74 %) and sorghum (0.28 %) a 2.6-fold gap is large enough to predict biologically meaningful efects on muscle-protein deposition, based on dose-response data from pelleted-diet trials in commercial rabbit breeds [1,14,15] .

Conclusion

This research set out to characterise the essential amino acid profiles and fibre fractions of five hydroponic sprout species and to map those profiles against the nutritional requirements of meat-type breeding programmes for small herbivores, using the growing rabbit as the reference animal. The data provide a nutrient-detail layer that is absent from the existing hydroponic-feed literature, which has relied almost exclusively on proximate analysis. Among the five species, cowpea and mung bean sprouts delivered the highest total essential amino acid concentrations and the best lysine and threonine levels both at or above NRC requirements for growing rabbits. Maize sprouts supplied the most methionine among the species tested, though still well below the combined methionine-plus-cystine requirement. Sorghum scored lowest on both amino acid and fibre quality metrics, with the highest ADL and lowest total EAA, making it the least suitable hydroponic species for precision rabbit nutrition. Based on these profiles, a blended-sprout strategy combining approximately 60 % cereal (maize) and 40 % legume (cowpea or mung bean) on a DM basis would satisfy both lysine and methionine thresholds while keeping the NDF: ADL ratio within a range favourable for caecal fermentation. This approach could reduce or eliminate the need for imported synthetic amino acids in smallholder rabbit operations across West Africa. Future research should validate these compositional findings through live-animal feeding trials that measure daily gain, FCR, carcass traits, and amino acid digestibility coeficients. Testing additional legume species pigeon pea, groundnut, bambara bean would broaden the menu of locally available options. Seasonal repetition of the sprout characterisation during the dry season, when greenhouse temperatures may exceed 35 °C, would test whether the amino acid and fibre profiles remain stable under heat stress. Finally, on-farm participatory trials with smallholder rabbit breeders in the Ashanti and Northern regions of Ghana would assess the practical scalability, labour demand, and economic viability of the multi-species sprouting approach.

Acknowledgement

Acknowledgements Contributions Not Qualifying for AuthorshipThe authors thank Mr. Samuel Owusu and Ms. Esther Agyemang for their assistance with greenhouse management, sample preparation, and laboratory analyses throughout the research period.

References

1. De Blas C, Wiseman J. Nutrition of the Rabbit. 2nd ed. Wallingford: CABI Publishing; 2010.
2. Lukefahr SD, Cheeke PR. Rabbit project development strategies in subsistence farming systems. World Anim Rev. 2015;68:60-70.
3. Oseni SO, Lukefahr SD. Rabbit production in low-input systems in Africa: situation, knowledge and perspectives. World Rabbit Sci. 2014;22(2):147-160.
4. Naik PK, Swain BK, Singh NP. Production and utilisation of hydroponics fodder. Indian J Anim Nutr. 2015;32(1):19.
5. Al-Sagheer AA, Abdel-Rahman GA, Elsawy SA. Potential of hydroponic barley fodder as a feed supplement for ruminants in hot arid regions. Trop Anim Health Prod. 2019;51(5):1209-1217.
6. Gidenne T, García J, Lebas F, Licois D. Nutrition and feeding strategy: interactions with pathology. In: De Blas C, Wiseman J, editors. Nutrition of the Rabbit. CABI; 2010. p. 179-199.
7. Van Soest PJ, Robertson JB, Lewis BA. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J Dairy Sci. 1991;74(10):3583-3597.
8. Gidenne T. Dietary fibres in the nutrition of the growing rabbit and recommendations to preserve digestive health: a review. Animal. 2015;9(2):227-242.
9. Mateos GG, Rebollar PG, De Blas C. Minerals, vitamins and additives. In: De Blas C, Wiseman J, editors. Nutrition of the Rabbit. CABI; 2010. p. 119-150.
10. Aganga AA, Tshwenyane SO. Potentials of guinea grass (Panicum maximum) as forage crop in animal nutrition. Pak J Nutr. 2004;3(1):1-4.
11. Lebas F, Coudert P, De Rochambeau H, Thébault RG. The Rabbit: Husbandry, Health and Production. Rome: FAO; 1997.
12. Morgan J, Hunter RR, O'Haire R. Limiting factors in hydroponic barley grass production. In: Proceedings of the 8th International Congress on Soilless Culture. 1992:241261.
13. Cuddeford D. Hydroponic grass. In Practice. 1989;11(5):211-214.
14. Makkar HPS. Efects and fate of tannins ingested by ruminants through the consumption of tannin-rich feeds. J Anim Sci. 2003;81(6):1549-1560.
15. Reddy GVN, Reddy MR, Reddy KK. Nutrient utilisation by milch catle fed on hydroponic barley fodder. Indian J Anim Nutr. 2014;31(1):63-68.
16. Fazaeli H, Golmohammadi HA, Tabatabayee SN, AsghariTabrizi M. Productivity and nutritive value of barley green fodder yield in hydroponic system. World Appl Sci J. 2012;16(4):531-539.
17. Sneath R, McIntosh F. Review of hydroponic fodder production for beef catle. Meat Livest Aust Rep. 2003;1:154.
18. Dung DD, Godwin IR, Nolan JV. Nutrient content and in sacco digestibility of barley grain and sprouted barley. J Anim Vet Adv. 2010;9(19):2485-2492.
19. Peer DJ, Leeson S. Nutrient content of hydroponically sprouted barley. Anim Feed Sci Technol. 1985;13(34):191-202.
20. Moin TM, Salam NB, Sarker T, Islam SS, Sun MA. Biomass production and nutritive value of diferent hydroponic fodder species and their efects on growth performance on rabbits. South Asian J Agric Sci. 2023;3(2):49-54.