Advancing nutrient utilization, gut health, animal performance and sustainable livestock production

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ABSTRACT Modern animal nutrition is increasingly focused on converting a greater proportion of feed nutrients into productive output while supporting gastrointestinal health, reducing nutrient losses and improving production resilience. Exogenous feed enzymes and probiotics are central biological tools in this transition. Enzymes act primarily on feed substrates: phytase releases phytate-bound phosphorus; xylanase, β-glucanase, mannanase and cellulase modify complex plant carbohydrates; protease improves protein and amino-acid utilization; and amylase and specialty enzymes can complement endogenous digestion. Probiotics act mainly through the gastrointestinal or ruminal ecosystem by influencing microbial competition, fermentation, intestinal barrier function, immune signalling and digestive activity. Their effects are highly dependent on enzyme activity, probiotic strain, dose, diet, animal species, age, health status and feed-processing conditions. Used as part of a precisely formulated nutritional strategy, enzymes and probiotics can improve nutrient digestibility, feed efficiency, gut function and environmental performance across poultry, swine, ruminants and aquaculture.

Keywords: feed enzymes, probiotics, phytase, xylanase, protease, Bacillus, gut health, nutrient digestibility, feed conversion, poultry, swine, ruminants, aquaculture, sustainability

1. Introduction: From Feed Supply to Nutrient Efficiency

Feed is the dominant biological input in animal production, and its value depends not only on nutrient composition but on how effectively those nutrients are digested, absorbed and converted into meat, milk, eggs or biomass. Even a well-formulated diet contains fractions that the animal cannot completely utilize. Plant ingredients may contain phytate, arabinoxylans, β-glucans, mannans, cellulose and structurally resistant protein fractions. Heat processing can change starch and protein availability, while young animals may have limited endogenous digestive capacity. Nutrients escaping digestion are economically lost and can become substrates for undesirable hindgut fermentation or be excreted into the environment.

Feed enzymes and probiotics address these limitations through different but complementary biological mechanisms. Exogenous enzymes accelerate specific hydrolytic reactions and improve access to nutrients that are otherwise trapped, bound or poorly digested. Probiotics – usually selected bacterial or yeast strains – influence the biological environment of the gut or rumen. They may compete with undesirable microorganisms, produce metabolites, interact with epithelial and immune systems, and modify fermentation. The practical opportunity is therefore larger than a simple additive effect: enzymes can change the quantity and form of substrate reaching the microbiome, while probiotics can influence how that altered substrate is fermented and used.

2. Feed Enzymes: Unlocking Nutritional Value

The efficacy of an enzyme depends on matching a defined catalytic activity with a meaningful concentration of its target substrate, under the pH, temperature, moisture and transit-time conditions encountered in feed manufacture and the gastrointestinal tract. An enzyme should therefore be evaluated by retained activity and biological response, not by inclusion rate alone.

Enzyme	Principal substrate	Nutritional role
Phytase	Phytate / phytic acid	Releases phosphorus; improves mineral utilization; reduces phosphorus loss
Xylanase	Arabinoxylans / xylans	Reduces NSP effects, opens plant cell-wall structures and improves nutrient access
β-Glucanase	β-Glucans	Reduces viscosity in suitable cereal diets and supports nutrient diffusion
Mannanase	β-Mannans	Hydrolyses mannans and may improve use of soybean- and palm-derived ingredients
Cellulase	Cellulosic fibre	Supports fibre breakdown and release of entrapped nutrients in selected feed matrices
Protease	Dietary proteins	Complements endogenous proteolysis and improves protein/amino-acid utilization
Amylase	Starch	Supports starch hydrolysis where endogenous capacity or starch accessibility is limiting
Multi-enzyme systems	Multiple substrates	Targets several nutritional barriers in complex diets

2.1 Phytase – phosphorus efficiency and phytate destruction

In cereals and oilseed meals, a substantial proportion of phosphorus is stored as phytate. Monogastric animals have limited endogenous ability to hydrolyse this molecule. Supplemental phytase progressively removes phosphate groups, making phosphorus more available and reducing reliance on inorganic phosphate. Phytate degradation can also lessen interactions between phytate and minerals, proteins and digestive enzymes. Research in pigs has repeatedly shown improved phosphorus digestibility and lower phosphorus excretion when phytase is appropriately used in low-phosphorus diets. This makes phytase a strong example of an additive that links nutrition, feed cost management and environmental stewardship.

2.2 Carbohydrases – xylanase, β-glucanase, mannanase and cellulase

Non-starch polysaccharides (NSP) can impair digestion by increasing digesta viscosity, encapsulating starch and protein within plant cell walls and altering the substrates presented to intestinal microbes. Xylanase targets arabinoxylans; β-glucanase hydrolyses β-glucans; mannanase acts on β-mannans; and cellulase supports degradation of cellulosic structures. In wheat-based broiler diets, xylanase has been shown to improve body-weight gain, feed-to-gain ratio and ileal digestibility of crude protein and starch. The modern interpretation of carbohydrase action extends beyond viscosity reduction: controlled hydrolysis can open cell-wall structures and generate smaller carbohydrate fragments that change hindgut fermentation patterns.

2.3 Protease, amylase and multi-enzyme design

Protein ingredients differ widely in digestibility because of raw-material origin, processing history, anti-nutritional factors and protein structure. Supplemental protease complements gastric and pancreatic proteolysis, potentially increasing amino-acid release and reducing the flow of undigested protein into the hindgut. Amylase may support starch utilization where endogenous enzyme secretion, feed processing or starch structure limits digestion. In practical diets, several barriers occur at the same time; consequently, xylanase-amylase-protease combinations, often alongside phytase, can be more rational than treating each nutrient constraint in isolation. The key is not the number of enzymes in a blend but whether each activity has a relevant substrate and remains active under the intended manufacturing and digestive conditions.

3. Probiotics: Managing the Gastrointestinal Ecosystem

Probiotics used in animal nutrition are live microorganisms supplied in sufficient quantity to achieve a beneficial effect in the host. Commonly studied groups include spore-forming Bacillus species, lactic-acid bacteria, Clostridium butyricum and yeasts such as Saccharomyces cerevisiae. Their effects are strain specific: results obtained with one Bacillus subtilis strain, for example, cannot automatically be assigned to every B. subtilis product. A useful probiotic must combine biological efficacy with identity, safety, manufacturability, stability and viable recovery at the point of feeding.

3.1 Mechanisms supporting gut function

Competitive exclusion and ecological balance: Beneficial microorganisms can compete for attachment sites and nutrients, modify local pH and produce metabolites that make the intestinal environment less favourable to undesirable organisms. Bacillus-based broiler studies have reported changes in intestinal microbial populations together with improved performance under specific production conditions.

Barrier integrity and intestinal morphology: A healthy epithelium depends on villus architecture, crypt dynamics, mucus production and tight-junction integrity. Selected probiotics have been associated with improvements in villus characteristics, barrier-related responses and immune indices, supporting a larger and more functional absorptive surface.

Fermentation metabolites: Microbial fermentation can produce short-chain fatty acids such as acetate, propionate and butyrate. These compounds participate in epithelial energy metabolism, microbial cross-feeding and signalling. The pattern of metabolite production depends on diet, strain composition and the resident microbiota.

Digestive contribution: Some Bacillus and lactic-acid bacterial strains produce extracellular proteases, amylases, lipases or carbohydrases. This does not make a probiotic equivalent to a standardized feed enzyme, but it can provide an additional mechanism by which selected strains support nutrient utilization.

4. Application Across Animal Species

4.1 Poultry

Poultry is one of the most developed markets for enzyme and probiotic nutrition because feed intake is high relative to body size, production cycles are short and cereal-oilseed diets contain multiple enzyme substrates. Phytase improves phosphorus use; xylanase and other carbohydrases address NSP; protease supports amino-acid utilization; and multi-enzyme systems improve access to entrapped nutrients. Probiotics may complement these effects by supporting microbial balance and intestinal function. Responses are often most visible when diets contain a defined nutritional constraint or birds face microbial, environmental or management stress.

4.2 Swine

In swine, phytase is fundamental to plant-based diet formulation because it improves utilization of phytate phosphorus and can reduce manure phosphorus. Carbohydrases are relevant as fibre inclusion increases or as alternative ingredients are used, while protease can support lower-crude-protein, amino-acid-balanced strategies. Probiotics are especially relevant around weaning, when abrupt dietary change, an immature digestive system and microbial instability increase the risk of poor nutrient utilization. Selection should consider strain, viability, diet composition and age rather than CFU inclusion alone.

4.3 Ruminants

Ruminant nutrition is distinct because the rumen itself is a large microbial fermentation chamber. Yeast cultures and live yeast products based on S. cerevisiae have been investigated for effects on ruminal pH, volatile fatty acids, microbial activity and performance. In one trial with high-yielding dairy cows, S. cerevisiae culture increased rumen pH and was associated with higher milk yield and milk fat. Responses across studies are variable, emphasizing that basal ration, stage of lactation, dose and rumen conditions strongly influence outcome. Exogenous fibrolytic enzymes may also be used to increase accessibility of fibrous feed components, but their benefit depends on substrate and method of application.

4.4 Aquaculture

Aquaculture adds another dimension because feed efficiency, intestinal health and water quality are closely linked. Probiotic Bacillus and lactic-acid bacterial systems are studied for growth, gut morphology, digestive activity, immune responses and microbial management. In Nile tilapia raised in biofloc systems, commercial probiotic treatments have been evaluated for effects on growth, intestinal histomorphology and microbiota. Enzymes can be particularly relevant as aquafeeds incorporate more plant proteins, cereals and co-products with phytate, fibre and complex carbohydrates. Successful aquafeed strategies therefore need to consider both digestibility within the animal and nutrient discharge into the culture environment.

5. Enzyme-Probiotic Synergy: Toward Integrated Biological Nutrition

The strongest conceptual case for combining enzymes and probiotics is that they act at different levels of the same digestive ecosystem. Enzymes alter the chemical form and availability of feed substrates; probiotics influence which microorganisms encounter those substrates and how fermentation proceeds. Carbohydrases may release oligosaccharides and reduce encapsulation of nutrients. Protease can decrease the amount of undigested protein reaching the hindgut. Phytase changes mineral availability and phytate load. A probiotic can then influence microbial competition, metabolite production and epithelial responses. In broiler research, a multi-strain Bacillus probiotic has been evaluated alongside xylanase-amylase and xylanase-amylase-protease systems, demonstrating that interactions between direct-fed microorganisms and enzymes can influence energy and nutrient utilization. The practical lesson is to formulate combinations around a defined nutritional problem rather than assuming that every enzyme-probiotic pair will be synergistic.

6. Stability, Feed Processing and Delivery

Biological efficacy begins before the additive reaches the animal. Conditioning, pelleting, extrusion, moisture, pressure, shear, mineral premixes, storage temperature and time can all reduce enzyme activity or probiotic viability. For enzymes, retained catalytic activity after feed manufacture is more meaningful than the activity added to the mixer. Thermostable enzyme proteins, granulation, protective coatings and post-pellet liquid application are common approaches to protect performance. For probiotics, viable count at the point of consumption is critical. Spore-forming Bacillus species are attractive partly because spores tolerate environmental stress, although stability remains strain- and formulation-dependent. Non-spore-forming organisms may require stronger protection or alternative delivery routes.

FORMULATION CHECKPOINTS • Define the nutritional barrier and quantify the relevant substrate in the diet. • Select enzyme activity or probiotic strain for the target animal and production stage. • Confirm compatibility with pH, feed-processing temperature, minerals, acids, and other additives. • Validate retained enzyme activity or viable CFU after manufacture and throughout shelf life. • Measure biological response through digestibility, performance, gut-health or environmental endpoints.

7. Sustainability and Resource Efficiency

The sustainability value of biological feed additives is primarily created through better nutrient capture. Phytase can decrease dependence on inorganic phosphorus and reduce phosphorus excretion. Protease and improved protein nutrition can support more efficient nitrogen utilization and lower the amount of undigested protein reaching the hindgut. Carbohydrases can increase the usable value of cereal fibre and agricultural co-products. If feed conversion improves, less feed may be required per unit of animal output. In aquaculture, better digestibility can also reduce nutrient loading of water. These benefits should be quantified against the actual commercial diet and production baseline; fixed universal percentage claims are rarely scientifically defensible.

8. Safety, Quality and Regulatory Considerations

For enzymes, quality control should include identity of the catalytic activity, activity specification, production-organism characterization, microbiological purity, relevant contaminants, formulation stability and batch-to-batch consistency. For probiotics, strain identity is fundamental. Safety cannot be inferred from genus or species name alone. The product should be supported by accurate strain characterization, absence of relevant safety concerns, defined viable count, microbiological purity and evidence of stability. Regulatory requirements differ by market and target species, so enzyme and probiotic products should be assessed under the applicable feed-additive framework before commercial use.

9. Why Responses Differ Between Studies and Farms

Variation in response is a defining feature of biological feed technologies. An additive can perform strongly in one diet and weakly in another because the substrate concentration, ingredient processing, nutrient density, animal age, microbiota, health status and production environment differ. Xylanase is unlikely to deliver a large response when little suitable arabinoxylan substrate is present; protease response depends on protein quality and digestibility; a probiotic may show its greatest benefit under microbial or environmental challenge. Dose, feed-processing losses and interactions with acids, minerals or other additives further influence response. For this reason, enzymes and probiotics should be selected as components of a nutritional system rather than treated as interchangeable commodity additives.

10. Future Directions: Precision Biological Nutrition

Future development is moving toward precision biological nutrition. Enzyme engineering is producing catalysts with improved thermostability, pH tolerance and substrate specificity. Better feed-matrix characterization will allow enzyme dosing to be linked to measurable substrate levels rather than fixed inclusion. Probiotic development is advancing toward strain-level genomics, metabolite profiling, microbiome-guided selection, host-specific isolates and combinations of strains with complementary functions. Some Bacillus strains may provide both probiotic activity and extracellular digestive enzymes, blurring the traditional boundary between enzyme and microbial technologies. The next generation of products is therefore likely to be designed around a systems question: which nutrients escape digestion, which microbial populations receive them, which metabolites result, and which combination of enzymes and microorganisms shifts that system toward better nutrient capture and a more resilient gut?

11. Conclusion

Feed enzymes improve what the animal can extract from the diet; probiotics influence the biological environment in which digestion and absorption occur. Phytase, carbohydrases, protease, amylase and multi-enzyme systems can increase access to phosphorus, carbohydrates, protein and energy. Selected probiotics can support microbial balance, epithelial function, fermentation and host responses. Their greatest value is realized when enzyme activity is matched to substrate, probiotic efficacy is demonstrated at the strain level, stability is maintained through processing and storage, and responses are validated under realistic feeding conditions. Used with this precision, enzymes and probiotics form an important platform for better feed efficiency, gastrointestinal health, resource utilization and sustainable production of animal protein.

Selected Scientific References

1. Zhang L, Xu J, Lei L, et al. Xylanase supplementation in wheat-based broiler diets. Asian-Australas J Anim Sci. 2014;27:855-861. doi:10.5713/ajas.2014.14006. 2. Harper AF, Kornegay ET, Schell TC. Phytase in low-phosphorus growing-finishing pig diets. J Anim Sci. 1997;75:3174-3186. doi:10.2527/1997.75123174x. 3. Arif M, Akteruzzaman M, Al-Ferdous T, et al. Bacillus-based probiotics in broilers. Vet Anim Sci. 2021;14:100216. doi:10.1016/j.vas.2021.100216.

4. Wealleans AL, Walsh MC, Romero LF, Ravindran V. Multi-enzyme combinations and a Bacillus probiotic in broilers. Poult Sci. 2017;96:4287-4297. doi:10.3382/ps/pex226. 5. Sun X, Wang Y, Wang E, et al. Saccharomyces cerevisiae culture in high-yield dairy cows. Animals. 2021;11:2401. doi:10.3390/ani11082401. 6. Asha AAA, et al. Commercial probiotics in Nile tilapia reared in biofloc technology. Biology. 2024;13:299. doi:10.3390/biology13050299.

Scientific note: The magnitude of performance, digestibility, microbiome and sustainability responses is diet-, strain-, dose-, species- and production-condition dependent. Product-specific claims should be supported by validated activity/viability data and controlled application trials.