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. 2026 Jun 4;22:473. doi: 10.1186/s12917-026-05608-3

Nutritional, antinutritional, and heavy metal profiles of ethnopoultry botanicals in Central Uganda

Alice Nabatanzi 1,✉, Maria Nakatoogo 2
PMCID: PMC13474668  PMID: 42243928

Abstract

In Central Uganda, smallholder farmers rely on indigenous ethnoveterinary botanicals as phytogenic feed additives (PFAs) for indigenous chickens (Gallus gallus domesticus). However, the balance between their nutritional benefits and toxicological risks remains poorly characterized. Following an ethnoveterinary survey in Najjembe sub-county where Capsicum frutescens (ranked 2nd ), Cannabis sativa (3rd ), and Nicotiana tabacum (4th) were prioritized by farmers, this study investigated their nutritional and safety profiles. Aloe vera (1st ) was excluded from analysis due to extensive prior documentation. Samples were analyzed for proximate, mineral, and antioxidant profiles using AOAC Official Methods. Antinutrients (tannins, oxalates, phytates) and heavy metals (Pb, Cd) were quantified using vanillin-HCl spectrophotometry and Atomic Absorption Spectrophotometry, respectively. Results showed significant nutritional variation among species (p < 0.05). C. sativa contained the highest crude protein (22.20 ± 1.1%) and was exceptionally rich in calcium and potassium. C. frutescens exhibited the highest caloric density (452.9 kcal/100 g) and antioxidant activity (IC50 = 11.78 mg/mL). Conversely, N. tabacum had the highest iron and magnesium but also the highest antinutrient concentrations. Critically, lead (Pb) and cadmium (Cd) levels in N. tabacum and C. sativa significantly exceeded FAO/WHO safety limits (Pb > 0.3 mg/kg), resulting in hazard indices (HI > 1.0), signaling potential health risks for chickens and consumers. While these plants offer high nutraceutical value, the heavy metal bioaccumulation in N. tabacum and C. sativa necessitates strict inclusion limits and processing to ensure food safety. C. frutescens is recommended as the most viable PFA for feed integration.

Keywords: Ethnopoultry, Phytogenic feed additives, Antinutrients, Heavy metals, Gallus gallus domesticus, Uganda

Introduction

In Uganda, the poultry industry is a cornerstone of rural marginalized communities, with indigenous chicken comprising over 80% of the national flock [1, 2]. These birds are important for food security and provide high-quality protein for smallholder households [3]. However, productivity is limited by high conventional feed costs and a high prevalence of infectious diseases, particularly Newcastle disease and coccidiosis [2, 4]. To manage these challenges, farmers integrate ethnoveterinary botanicals and non-conventional feed resources (NCFRs) into poultry management [4, 5]. In Central Uganda, the most common species are Cannabis sativa L. (“enjaga”), Nicotiana tabacum L. (“taaba”), and Capsicum frutescens L. (“kamulali”) [4]. These plants serve as both medicinal agents and nutritional enhancers, yet their use relies on indigenous knowledge rather than established safety standards.

Cannabis sativa is traditionally used to manage severe viral and bacterial symptoms, specifically the gasping and respiratory distress typical of Newcastle disease and the profuse diarrhea associated with infectious bronchitis [4]. Beyond its medicinal use, the seeds contain 20–29% crude protein and essential omega fatty acids [6]. While low-level supplementation (0.8%) can improve feed conversion, its use is hindered by antinutritional factors (ANFs) such as phytic acid and high crude fiber [7]. Similarly, N. tabacum is used to control internal parasites and respiratory infections [4]. Its leaves contain up to 52% protein a profile comparable to animal proteins like casein, but the presence of the toxic alkaloid nicotine is a major constraint [8, 9]. While chickens may tolerate nicotine levels up to 2%, higher concentrations are toxic [10].

Capsicum frutescens is a widely used phytogenic feed additive (PFA) for coccidiosis management and Newcastle disease prophylaxis [11, 12]. The fruits are rich in capsaicinoids and phenols, which provide antimicrobial benefits and can increase carcass yield by 15% at a 2.2% inclusion rate [13]. However, higher concentrations (4.4%) have been linked to reduced intestinal weight, likely due to high levels of tannins and saponins [13].

Despite the widespread trust in these remedies, there is little data to balance their nutritional value against antinutritional and heavy-metal risks. This study characterized the nutritional and antinutritional properties of C. sativa, N. tabacum, and C. frutescens. This evaluation establishes a scientific basis for the safe integration of these species into indigenous chicken feeding regimes and their potential development into standardized poultry nutraceuticals.

Materials and methods

Plant selection and collection

A cross-sectional ethnoveterinary survey was conducted in Najjembe sub-county, Buikwe District, Uganda, from January to September 2021. The survey documented 59 plant species used to treat poultry diseases [4]. Among the six most frequently reported species, Capsicum frutescens, Cannabis sativa, and Nicotiana tabacum were prioritized for analysis as they consistently ranked 2nd, 3rd, and 4th, respectively, in preference and pairwise ranking exercises. Aloe vera, which ranked 1st, was excluded from this study as its profile is already extensively documented in literature.

Field expeditions were conducted in Najjembe (0° 24’ 11” N, 33° 1’ 54” E) guided by local poultry farmers. Fresh samples of C. sativa (leaves), N. tabacum (leaves), and C. frutescens (ripe fruits) (Fig. 1) were harvested in the morning to ensure metabolic stability and minimize heat-induced nutrient degradation [14]. Species were identified by Mr. Protase Rwaburindore, a taxonomist at the Makerere University Herbarium (MHU), and voucher specimens were deposited under accession numbers AN66, AN100, and AN99.

Fig. 1.

Fig. 1

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Selected ethnopoultry botanicals: (a) Cannabis sativa (leaves), (b) Nicotiana tabacum (leaves), and (c) Capsicum frutescens (Ripe fruits)

Approximately 100 kg of fresh material per species was collected to account for the high moisture content of fresh plants and to ensure sufficient dry matter for triplicate analysis across proximate, mineral, antinutrient, and heavy metal protocols. Samples were transported in ventilated sacks to allow for ambient airflow, preventing heat buildup and premature fermentation during transit.

Sample preparation

Fresh samples were cleaned with distilled water to remove contaminants. Leaves of C. sativa and N. tabacum were air-dried at room temperature for 14 days, while C. frutescens fruits were oven-dried at 40 °C for 2 h. To ensure uniform moisture removal across the large sample volume (100 kg fresh weight), all materials were subsequently dried at 40 °C for 24 h until reaching a constant weight. Samples were pulverized using a Brook Crompton grinder (Series 2000, UK) and stored in airtight bottles. Triplicate analyses were performed according to AOAC standards at the Makerere University Food Science Laboratory.

Proximate composition

Crude protein

Protein content was determined using the Kjeldahl method (AOAC 2001.11) [15]. The Kjeldahl method was selected over the Dumas method for its specific suitability in characterizing nitrogen in diverse ethnobotanical matrices within regional laboratory settings. Samples (1 g) were digested with 12 mL of 98% sulphuric acid at 420 °C for 60 min (Velp Scientifica DK 6/48). Distillation was performed using a Kjeltec 8200 auto-system with 40% NaOH and 4% boric acid. Distillates were titrated against 0.1000 M HCl. A conversion factor of 6.25 was used to calculate crude protein.

Moisture and ash content

Moisture content was determined by air-oven drying at 105 °C for 72 h (AOAC 925.10) [16]. Ash content was measured by incineration at 550 °C for 2 h in a muffle furnace (AOAC 942.05) [15]. A temperature of 550 °C was used rather than 600 °C to minimize the volatilization of specific minerals, such as potassium, ensuring a more accurate mineral profile for subsequent analysis.

Crude fat

Fat was extracted via the Soxhlet method (AOAC 920.39) [15] using hexane as the solvent for 6 h. The solvent was evaporated at 102 °C, and the remaining residue was weighed and expressed as a percentage of dry weight.

Crude fibre

Fibre content was determined using the Weende Method (AOAC 962.09) [15]. Fat-free samples underwent sequential digestion with 1.25% H2SO4 and 1.25% NaOH. Crude fibre was calculated as the weight loss following the incineration of the dried residue.

Carbohydrate and energy content

The total carbohydrate was calculated as crude by the difference:

% Total Carbohydrate = 100−(% Moisture+% Crude Protein+% Total Fat+% Ash).

Metabolizable energy was estimated using Atwater general factors: 4.0 kcal/g for protein and carbohydrates, and 9.0 kcal/g for lipids.

Micronutrient and antioxidant composition

Mineral analysis

Concentrations of Ca, Fe, Mg, Zn, Cu, Mn, Na, and K were determined using Atomic Absorption Spectrophotometry (PerkinElmer AAnalyst 700) AOAC Official Method 985.35 [15] following wet digestion with a HNO3/HClO4/H2SO4 mixture (9:2:1 v/v). Phosphorus was measured colorimetrically at 660 nm (AOAC 965.17) [15].

Heavy metals and selenium

Lead (Pb) and Cadmium (Cd) were quantified using anodic stripping voltammetry (Metrohm 946 Portable VA Analyzer) (AOAC 986.15 ) [15]. Selenium (Se) was determined using AAS with a hydride generation system. The use of hydride generation ensured maximum sensitivity for detecting trace levels of Se, which often exist below conventional flame-AAS detection limits.

Vitamin C and antioxidant activity

Vitamin C was determined using the 2,6-dichloroindophenol (DCPIP) titrimetric method, also known as the dye reduction method (AOAC 967.21) [15]. The absorbance was measured spectrophotometrically at 515 nm against a blank. The antioxidant activity was determined by using the 2, 2-diphenyl-1-pyrcyl hydrazyl (DPPH) radical scavenging assay as described by [17]. Absorbance was recorded at 517 nm, and the IC50 value (concentration required to inhibit 50% of DPPH radicals) was calculated via linear regression.

Antinutrients analysis

The tannin content was determined according to [18] using the vanillin-HCl spectrophotometric method at 500 nm, with catechin as the standard. The phytate content was determined using the Wheeler and Ferrel method [19] and Ferrel titration method, using Iron (III) chloride to precipitate ferric phytate. Oxalates were determined using permanganatometric redox titration [20] and Ferrel titration method, using Iron (III) chloride to precipitate ferric phytate. Samples were extracted with 0.25 N HCl, precipitated as calcium oxalate, and titrated against standardized 0.05 N KMnO4 at 60–70 °C.

Risk-benefit analysis

The Hazard Quotient (HQ) [21] was calculated to assess the toxicological risk to chickens by comparing estimated daily intake (EDI) to the established poultry oral reference dose (RfDpoultry). To estimate human consumer risk, the target hazard quotient (THQ) [21] was calculated using a Bio-Transfer Factor (BTF) of 0.01– 0.1 to account for heavy metal translocation from botanical feed to muscle tissue. The cumulative risk from multiple metals (Pb and Cd) was expressed as the Hazard Index (HI), hazard [22], where:

Statistical analysis

Data were analyzed using IBM SPSS Statistics (v26.0). Results are presented as mean ± standard deviation of triplicate determinations. Differences in nutritional, antinutritional, and heavy metal concentrations across the three plant species were evaluated using one-way Analysis of Variance (ANOVA). Where significant differences were detected, Tukey’s Honestly Significant Difference (HSD) post-hoc test was applied for mean separation. Statistical significance was defined at p < 0.05.

Results

Proximate composition and energy values

The proximate profiles of C. sativa, C. frutescens, and N. tabacum are summarized in Table 1. Statistical analysis revealed significant differences (p < 0.05) in all nutritional parameters across the three species. C. sativa contained the highest crude protein (22.20 ± 0.38%), while C. frutescens exhibited the highest crude fiber and caloric density. Ash content was substantially higher in C. sativa and N. tabacum compared to C. frutescens. Total fats remained consistently low across all samples (≤ 1.14%).

Table 1.

Proximate composition and energy values of C. sativa (Leaves), C. frutescens (Fruits), and N. tabacum (Leaves) used in indigenous poultry systems

Parameter C. sativa  C. frutescens N. tabacum p-value
Crude protein (%) 22.20±0.38a 17.80±1.06c 20.57±0.96b <0.001
Crude fibre (%) 29.39±0.83b 36.51±0.48a 19.46±1.23c <0.001
Ash content (%) 18.31±0.09a 7.09±0.01b 17.85±0.10a <0.001
Total fat   (%) 0.97±0.05b 1.14±0.06a 0.90±0.14b 0.038
Total carbohydrates (%) 5.35±0.64b 9.33±1.06a 5.82±0.75b 0.002
Moisture content (%) 3.62±0.11b 2.31±0.07c 4.80±0.44a 0.001
Energy (Kcal/ 100g) 353.4±1.41b 452.9±3.54a 345.7±3.54b <0.001
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Values are Mean ± SD (n=3) on a dry weight basis. Means in a row with different superscripts are significantly different (p<0.05)

Micronutrient and antioxidant profiles

Mineral and vitamin profiles varied significantly (p < 0.05) among species (Table 2). C. sativa was superior in calcium and potassium, while N. tabacum recorded the highest magnesium and iron levels. C. frutescens contained the highest Vitamin C and copper concentrations but showed the lowest overall mineral residue. Selenium remained undetectable across all samples. In the DPPH assay, C. frutescens demonstrated the strongest antioxidant activity (IC50 = 11.78 ± 0.33 mg/mL) followed by C. sativa and N. tabacum.

Table 2.

Micronutrient and Antioxidant Composition of C. sativa (Leaves), C. frutescens (Fruits), and N. tabacum (Leaves) used in indigenous poultry systems

Parameter (mg/100 g) Micronutrient Composition p-value
C. sativa C. frutescens N.tabacum
Sodium 0.74 ± 0.02c 1.35 ± 0.35b 2.15 ± 0.04a 0.002
Potassium 4945 ± 15.25a 334.9 ± 1.51c 1999 ± 1.26b < 0.001
Calcium 5695 ± 8.84a 18.58 ± 0.48c 3501 ± 0.19b < 0.001
Magnesium 460.3 ± 1.11b 23.29 ± 0.05c 830.4 ± 0.02a < 0.001
Copper 0.13 ± 0.01c 0.98 ± 0.07a 0.56 ± 0.03b 0.001
Iron 12.93 ± 0.34b 5.95 ± 0.11c 49.73 ± 0.99a < 0.001
Phosphorus 344.5 ± 1.00a 146.5 ± 1.00c 277.5 ± 1.00b < 0.001
Zinc 11.33 ± 0.08a 7.27 ± 0.50b 10.64 ± 0.32a 0.005
Manganese 1.93 ± 0.08a 0.89 ± 0.07b 0.23 ± 0.03c < 0.001
Selenium ND ND ND -
Vitamin C 73.83 ± 3.32c 96.78 ± 5.03a 85.66 ± 5.35b 0.004
Total antioxidants IC50* 14.69 ± 0.52b 11.78 ± 0.33c 27.94 ± 0.37a < 0.001
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*Values are Mean ± SD. ND: Not Detected. IC50 in mg/mL (lower value indicates higher activity). Ascorbic acid standard IC50 = 0.028 mg/mL

Antinutrient and heavy metal profiles

The antinutrient and heavy metal concentrations are summarised in Table 3. Nicotiana tabacum contained the highest concentrations across all safety parameters (p < 0.05). Its tannin content (467.40 ± 68.99 mg/g GAE) was approximately double that of C. sativa and C. frutescens. A similar trend was observed for phytates and oxalates. Regarding heavy metal bioaccumulation, N. tabacum and C. sativa recorded the highest levels of cadmium and lead, both significantly exceeding the concentrations found in C. frutescens.

Table 3.

Antinutrient and Heavy metal profiles of C. sativa (Leaves), C. frutescens (Fruits), and N. tabacum (Leaves) used in indigenous poultry systems

Parameter C. sativa C. frutescens N. tabacum p-value
Total tannins (mg/g GAE) 275.90 ± 32.73b 274.80 ± 21.96b 467.40 ± 68.99a 0.003
Phytate content (g/100 g) 9.15 ± 3.90a 6.93 ± 1.43a 11.63 ± 3.30a 0.214
Oxalate content (g/100 g) 12.34 ± 2.58b 15.11 ± 2.33b 23.68 ± 3.44a 0.008
Cadmium (mg/100 g) 0.08 ± 0.02b 0.03 ± 0.002c 0.17 ± 0.006a < 0.001
Lead (mg/100 g) 1.39 ± 0.37b 0.29 ± 0.03c 2.06 ± 0.20a < 0.001
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Values are Mean ± SD (n = 3) on a dry weight basis. Means in a row with different superscripts are significantly different (p < 0.05)

Regulatory compliance and risk assessment

Heavy metal concentrations were benchmarked against FAO/WHO Codex Alimentarius and EU safety limits [23] (Table 4) and the maximum levels (MLs) established by the European Union [24–26]. Cadmium levels in N. tabacum (1.7 mg/kg) exceeded the FAO/WHO leafy vegetable limit (0.20 mg/kg) by 8.5-fold. Lead levels in both N. tabacum (20.6 mg/kg) and C. sativa (13.9 mg/kg) were notably higher than the EU Directive 2002/32/EC threshold (5.0 mg/kg) for complete poultry feed.

Table 4.

Heavy metal compliance status (concentrations in mg/kg)

Species Cadmium (Cd) Status Lead (Pb) Status
C. sativa 0.8 Exceeded 13.9 Exceeded
C. frutescens 0.3 Compliant* 2.9 Compliant
N. tabacum 1.7 Exceeded 20.6 Exceeded
EU Feed Limit 0.5–1.0 - 5.0 -
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*C. frutescens exceeded food limits but remained within poultry feed limits

Toxicological risk assessment (Table 5) revealed that the Hazard Quotient (HQ) for lead exceeded the unity threshold (HQ > 1), in both N. tabaccum (1.96) and C. sativa (1.32) indicating potential health concerns. Capsicum frutescens remained the only species with a safe toxicological profile (HI < 1).

Table 5.

Toxicological risk assessment (HQ, THQ, and HI)

Species Metal Poultry HQ Human THQ Hazard Index (HI)
C. sativa Pb / Cd 1.32 / 0.53 0.25 / 0.06 1.85
C. frutescens Pb / Cd 0.28 / 0.20 0.05 / 0.04 0.48
N. tabacum Pb / Cd 1.96 / 1.13 0.37 / 0.44 3.09
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HQ/THQ/HI > 1 indicates a significant risk threshold breach

Discussion

This study validates the nutritional and safety profiles of C. sativa, C. frutescens, and N. tabacum, which are central to ethnoveterinary practices in Central Uganda [4]. These plants demonstrate significant potential as protein and mineral concentrates for scavenging indigenous chickens (Gallus gallus domesticus). By providing concentrated nutrients, these botanicals function as nutraceuticals that bridge the nutritional gaps inherent in free-range systems, where protein and mineral deficiencies often limit productivity. However, the presence of antinutrients and heavy metals necessitates a cautious approach to their integration into standardized poultry feed.

Proximate composition and energy values

The crude protein (CP) concentrations in C. sativa (22.20%) and N. tabacum (20.57%) exceed the Recommended Daily Allowance (RDA) of 16–18% CP for indigenous chickens [27] but align with the intensive requirements of commercial broiler starter diets (22–24%) [28–30]. Integrating these plants at controlled levels (0.8%–2.0%) could mitigate the protein deficiencies found in traditional scavenging diets largely composed of maize bran (11.2% CP) and kitchen refuse, thereby accelerating growth and maturity in local breeds.

The caloric density of C. frutescens (452.9 kcal/100 g) represents a significant energy reserve compared to conventional poultry formulations (2800–3200 kcal/kg) [31]. Additionally, the high crude fiber content across all analyzed species (19.46%–36.51%) necessitates their use as supplements rather than basal feeds. Excessive fiber can impede digestibility in monogastrics [32]. However, moderate inclusion supports gut health by improving the villus-to-crypt ratio in the intestinal mucosa [33], thereby enhancing nutrient absorption and resilience against enteric pathogens in chickens. Furthermore, the high ash content in C. sativa (18.31%) and N. tabacum (17.85%) provides an important mineral buffer for skeletal development and eggshell formation [34, 35] in environments where mineral intake is sporadic. The heavy feeder nature of N. tabacum [36] reflects a rapid consumption of soil macronutrients. Since N. tabacum is actively cultivated in smallholder backyard gardens in Najjembe rather than harvested from unmanaged wild populations, farmers exercise direct control over its growing environment. However, the natural ferric soils and weathered ferrisols characteristic of the Lake Victoria Crescent are inherently prone to acute macronutrient leaching and depletion under continuous cropping. Therefore, targeted soil nutrient replenishment through organic composting or managed fallowing must be considered as a critical agronomic strategy [37, 38] to prevent localized soil degradation where these high-mineral ethnopoultry botanicals are intensively harvested.

Micronutrient composition and antioxidant activity

The calcium (Ca) content of C. sativa and the iron (Fe) content of N. tabacum far exceed values reported for maize bran [39]. Scavenging indigenous chickens often suffer from skeletal depletion and compromised skeletal integrity due to severe nutritional deficiencies, particularly a lack of adequate Ca, phosphorus (P), and vitamin D [40, 41]. Thus, C. sativa and N. tabacum could serve as concentrated mineral boosters. The high magnesium (Mg) levels in N. tabacum (830.4 mg/100 g) further support this by serving as a co-factor for enzymatic reactions important for bone mineralization and protein synthesis [42]. Additionally, the high Fe content in N. tabacum provides essential erythropoietic support in rural Uganda, where parasite-induced anemia is endemic among free-range chickens [43]. This is enhanced by the synergistic presence of Vitamin C in all analysed species, which facilitates the reduction of ferric iron (Fe³⁺) to the more bioavailable ferrous (Fe²⁺) form for intestinal absorption [44].

The antioxidant capacity of these botanicals offers a natural alternative to synthetic antioxidants like BHT [45]. While C. frutescens exhibited the highest in vitro activity, C. sativa contains phytocannabinoids (CBD) that activate the Nrf2 pathway, upregulating endogenous enzymes like glutathione peroxidase for systemic protection [46]. In Uganda’s tropical climate, high ambient temperatures cause heat stress, resulting in physiological dysfunction and death [47, 48]. Vitamin C serves as an immunomodulator that enhances humoral immunity and increases serum levels of immunoglobulins IgG and IgM, boosting resistance during hot and dry seasons [47, 48].

The micronutrient profiles serve as biological mirrors of the soil chemistry in Central Uganda [49]. High Fe and manganese (Mn) levels reflect the typical low pH (< 5.5) of Ugandan ferralsols, which increases the solubility and plant uptake of heavy metals [50]. Conversely, the high potassium (K) and Ca in C. sativa suggest these plants are efficient accumulators of cations [51]. The low phosphorus levels mirror the high P-fixation capacity of tropical soils [52]. Continuous harvesting of these high-mineral plants could lead to soil degradation where nutrient depletion outpaces natural replenishment, threatening long-term agricultural productivity [53, 54].

Antinutrients and heavy metal risks

The high concentrations of tannins, phytates, and oxalates, particularly in N. tabacum, present significant anti-nutritional challenges. Tannins in N. tabacum (467.40 mg/g GAE) can bind to dietary proteins and inhibit digestive enzymes like trypsin, impairing protein digestibility [55]. Phytate levels (11.63 g/100 g) act as potent chelators of essential minerals (Ca, Mg, Zn), potentially leading to skeletal deformities [56]. Furthermore, high oxalate levels in N. tabacum (23.68 g/100 g) and C. frutescens (15.11 g/100 g) reduce Ca bioavailability and can precipitate in renal tubules, causing renal damage [57]. Nicotiana tabacum and C. sativa are known hyperaccumulators of heavy metals [58, 59]. The high levels of Pb and Cd in N. tabacum suggest growth in soils contaminated by anthropogenic activities, such as phosphate fertilizer use or industrial runoff [60, 61]. While this makes them useful for phytoremediation, it poses risks of biomagnification within the food chain. Lead and Cd are non-biodegradable and accumulate in the liver, kidneys, and muscle tissues [62]. The Hazard Quotient (HQ) for N. tabacum exceeded the unity threshold for Pb (1.96) and Cd (1.13), suggesting cumulative intake exceeds the metabolic capacity of the chickens.

While individual THQs for human consumers remain below 1.0, the Hazard Index (HI) for N. tabacum (3.09) and C. sativa (1.85) reveals a significant cumulative toxic load. Lead and Cd act synergistically by competing with Ca for binding sites on proteins [63]. However, high phytate and oxalate levels in N. tabacum may bind to these heavy metals, potentially mitigating toxicity by aiding their excretion [64]. Processing strategies such as boiling can reduce tannin and oxalate loads [34, 65], while fermentation triggers microbial phytase activity to break down phytic acid, increasing mineral bioavailability [66, 67]. Finally, to mitigate risks, farmers must avoid harvesting from roadsides or industrial zones where heavy metal concentrations are elevated [68, 69].

Conclusion

This study characterizes C. sativa, C. frutescens, and N. tabacum as high-value nutraceuticals for indigenous chicken production in Central Uganda. These plants offer a viable solution to chronic protein and mineral deficiencies in free-range scavenging systems. The protein content of C. sativa and N. tabacum exceeded basic requirements and C. frutescens provided essential caloric and antioxidant support. However, the significant bioaccumulation of lead (Pb) and cadmium (Cd) in N. tabacum and C. sativa presents a clear toxicological risk within the poultry food chain, posing a One Health challenge. Furthermore, the high nutrient demand of these species suggests that intensive harvesting could accelerate soil nutrient depletion if not managed sustainably.

To balance nutritional benefits against toxicological risks, we recommend processing interventions such as boiling and fermentation to reduce antinutrient loads and enhance mineral bioavailability. Agronomic safeguards, particularly avoiding roadside or industrial harvest sites, are essential to mitigate heavy metal contamination. Ultimately, while these botanicals are a cost-effective alternative to conventional feeds, standardized dosing and strategic processing are necessary. Future research should focus on transfer factors from feed to eggs and meat to establish precise Maximum Residue Limits (MRLs) for heavy metals in poultry products derived from these species.

Acknowledgements

The authors acknowledge Chairman Magomu Safiyi of Mubango village, Najjembe sub-county, who guided us, together with the locals to the plant collection sites. We are indebted to all the poultry farmers in Najjembe sub-county who never hesitated to share their indigenous knowledge regarding the traditional uses of the analysed plant species. Special appreciation to Mr. Ofwono Stanley, who collected the voucher specimen. Mr. Emmanuel Okalany is highly appreciated for all his technical support during the laboratory experiments.

Abbreviations

ANFs

Antinutritional Factors

ANOVA

Analysis of Variance

AOAC

Association of Official Analytical Chemists

BHT

Butylated Hydroxytoluene

BTF

Bio-Transfer Factor

CBD

Cannabidiol

Cd

Cadmium

CP

Crude Protein

DCPIP

2,6-dichloroindophenol

DPPH

2,2-diphenyl-1-picrylhydrazyl

EDI

Estimated Daily Intake

EU

European Union

FAO

Food and Agriculture Organization

GAE

Gallic Acid Equivalents

HCl

Hydrochloric acid

HI

Hazard Index

HQ

Hazard Quotient

HSD

Honestly Significant Difference

IC50

Half-maximal Inhibitory Concentration

IgG / IgM

Immunoglobulin G / Immunoglobulin M

K

Potassium

L.

Linnaeus (Botanical authority reference)

MHU

Makerere University Herbarium

MLs

Maximum Levels

MRLs

Maximum Residue Limits

NCFRs

Non-Conventional Feed Resources

ND

Not Detected

Nrf2

Nuclear factor erythroid 2-related factor 2

Pb

Lead

PFAs

Phytogenic Feed Additives

RDA

Recommended Daily Allowance

SPSS

Statistical Package for the Social Sciences

THQ

Target Hazard Quotient

WHO

World Health Organization

Authors’ contributions

AN conceived the research idea, was involved in field data collection and manuscript writing, and was the project principal investigator. NM was involved in data analysis and manuscript writing. All the authors proofread and approved the final draft of the manuscript.

Funding

This study was funded by the Government of Uganda through the Makerere University Research and Innovations Fund (MAKRIF/DVCFA/026/20).

Data availability

This article has all the required data.

Declarations

Ethics approval and consent to participate

The study protocol was reviewed and approved by the Makerere University School of Health Sciences Research and Ethics review board (MAKSHSREC-2020-74). Permission to access Najjembe sub-county for plant collection was granted by the local area administration.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

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