Bacillus subtilis in Poultry Production: From Gut Health to Cost Efficiency

      In recent years, feed costs have come to account for more than 70% of total production expenses in the poultry industry. Finding ways to improve feed efficiency and lower costs is a pressing challenge for every farm. At the same time, the global move away from in-feed antibiotics has led to a noticeable rise in intestinal diseases. The pain of losing traditional preventive tools is real. One microbial feed additive – Bacillus subtilis – is steadily proving its value as a practical solution to these problems.

1. Strong resistance to feed processing

      Bacillus subtilis maintains its viability during feed processing, a major advantage over many conventional probiotics such as Lactobacillus.

      Poultry pellet production typically involves high temperature, high pressure and strong shearing forces. Most probiotic bacteria lose viability during pelleting, so that very few viable cells reach the farm. Bacillus subtilis, however, forms endospores. In the dormant spore form it can survive the physical stresses of feed processing, then germinate into active vegetative cells once inside the animal's intestine, where it exerts its beneficial effects.

      Studies show that Bacillus subtilis survives simulated gastric and intestinal juices much better than Lactobacillus or Bifidobacterium. This robustness underpins its reliable performance under real production conditions.

      On the market, formulations include powders, microencapsulated granules and liquid cultures – all designed to meet the viability requirements of different feed processing systems.

2. Strengthening the intestinal barrier and reducing inflammation

      A key mechanism by which Bacillus subtilis improves poultry health is through reinforcing the gut barrier and modulating inflammatory responses. In a post‑antibiotic era this matters greatly – problems once kept in check by antibiotics now need alternative tools.

      Under tropical stress conditions, heat stress damages intestinal mucosa, increases oxidative stress, impairs immunity and raises pathogen permeability, causing substantial economic losses. When broilers were fed Bacillus subtilis 14823 at 1×10⁶ or 1×10⁷ CFU/g feed, body weight and weight gain up to day 42 improved significantly, and feed conversion ratio was better than controls. In terms of gut morphology, duodenal villus height increased, crypt depth decreased, and the villus‑to‑crypt ratio increased. At the molecular level, mRNA expression of tight junction proteins (occludin, claudin‑1 and ZO‑1) was up‑regulated, while expression of five pro‑inflammatory cytokine genes was down‑regulated. Serum corticosterone levels also dropped. These findings clearly demonstrate that Bacillus subtilis protects intestinal integrity and exerts anti‑inflammatory effects under heat stress.

      Against necrotic enteritis, Bacillus subtilis also shows clear efficacy. Clostridium perfringens is the primary pathogen causing necrotic enteritis, and its infection rate has risen significantly since antibiotics were withdrawn. A study by Huazhong Agricultural University showed that adding a Bacillus subtilis‑based multi‑strain probiotic to broiler diets markedly reduced intestinal lesions after C. perfringens challenge. Compared with the challenged control group, birds receiving the probiotic had significantly higher body weight. Their jejunal villus structure was better preserved, and expression of tight‑junction proteins CLDN1 and ZO‑1 was higher. The authors concluded that the Bacillus subtilis preparation had good preventive activity against necrotic enteritis.

3. Enhancing growth performance and feed conversion

      For poultry operations, improvements in growth performance and feed efficiency are the most directly valuable outcomes.

      Data from a controlled study published in Poultry Science showed that broilers fed a low‑protein diet (13.5% crude protein) supplemented with Bacillus subtilis (1.0×10⁹ CFU/mL per day) reached a body weight of 2176±45 g at day 42, compared with 2023±51 g in controls – a gain of 7.6% (P=0.003). At the same time, feed intake in the supplemented group was 5.2% lower, and the feed conversion ratio dropped from 1.71 to 1.55. More feed intake was converted into body weight. Further analysis revealed higher jejunal α‑amylase activity and an increased proportion of beneficial bacteria such as Butyricicoccus and the phylum Firmicutes, partly explaining the improved feed efficiency.

      In laying hens, a 2025 Poultry Science study evaluated a multi‑strain probiotic containing Bacillus subtilis and Bacillus licheniformis in 468 Hy‑Line Brown hens (24 weeks old). At an inclusion rate of 0.02%, egg production during weeks 6‑7 increased by 2.8 percentage points, and feed‑to‑egg ratio improved by 3.8‑4.3% at several stages. By week 4, eggshell thickness had increased by 5.3%; by week 6, eggshell strength improved by 24%. Haugh unit and albumen height showed sustained improvements through mid‑laying. Serum parameters: HDL cholesterol rose by 18.6%, immunoglobulins IgA and IgG increased by 23.4% and 19.8% respectively.

      Domestic research provides additional support. In a trial with 55‑62 week old layers, adding 200 mg/kg of a Bacillus subtilis product increased both laying rate and feed conversion. A combination of exogenous enzymes plus Bacillus subtilis gave the greatest improvements in eggshell thickness, Haugh unit and albumen height, as well as in apparent metabolizability of calcium, phosphorus and dry matter. Another study in Da‐gu chickens showed that Bacillus subtilis increased eggshell strength by 4.93%, shell thickness by 5.41% and Haugh unit by 3.00%, while significantly raising serum glutathione peroxidase activity and lowering malondialdehyde by 14.42%, confirming both egg quality and antioxidant benefits.

4. Modulating gut microbiota and reducing harmful emissions

      Optimising the gut microbiota is another important aspect of Bacillus subtilis action. A study in growing layers found that after Bacillus subtilis supplementation, caecal Lactobacillus counts increased by 1.2 log units, Escherichia coli decreased by 0.8 log units, and caecal microbial diversity increased.

      The shift in caecal microbiota changes the profile of fermentation end‑products. One study found that metabolites secreted by Bacillus subtilis – xanthine, niacin and pantothenic acid – play synergistic roles under multiple enteritis challenge conditions. Niacin and pantothenic acid reduce mucosal inflammation by suppressing the AP‑1 and NF‑κB pathways; xanthine up‑regulates intestinal mucus expression, strengthening the physical barrier. Together they also increase production of short‑chain fatty acids (acetate, butyrate and propionate), thereby supporting gut health and production resilience.

     An additional extra‑intestinal benefit is a clear reduction in faecal harmful gas emissions. Ammonia and hydrogen sulphide in poultry houses compromise bird health and worsen the working environment, as well as raising environmental compliance pressure. In the same layer study, faecal ammonia and hydrogen sulphide emissions fell by 34.7% and 28.3% respectively. Bacillus subtilis is also widely used in fermentation of soybean meal, corn straw and other feed ingredients, where its strong enzyme‑producing ability helps degrade macromolecular nutrients, reduce some anti‑nutritional factors, and improve palatability and overall nutritive value.

5. Potential as an antibiotic alternative and in fermented feeds

      Over‑reliance on antibiotics disturbs gut microbiota, promotes resistance and risks drug residues in end products. With its spore stability, high secretory protein capacity and well‑developed fermentation technology, Bacillus subtilis is now available in powders, granules and liquid formulations. As part of an antibiotic‑reduction strategy it fits the economic needs of both feed mills and farms.

      On cost reduction, Bacillus subtilis also performs well in fermented feed. When inoculated into soybean meal or corn straw, it produces extracellular hydrolases such as proteases and cellulases, breaking down large proteins and cellulose into small peptides and glucose, while lowering anti‑nutritional factors and greatly improving nutritive value. Fermented feeds can partially replace fishmeal or other concentrated protein sources, moderately lowering dietary costs while maintaining production efficiency. A study on Bacillus subtilis‑fermented soybean meal confirmed that macromolecular proteins are effectively degraded into small peptides, with particularly strong degradation of antigenic proteins, markedly enhancing the value of soybean meal.

Closing remarks and practical tips

     From gut health and feed efficiency to growth performance and environmental improvement, Bacillus subtilis is becoming a key component in the poultry industry's transition away from high antibiotic use toward greener, more efficient production. Whether it is faster broiler growth or better egg quality in later laying phases, abundant research data and field experience point to the strong potential of this probiotic.

      A few practical points deserve attention. First, the recommended effective dose typically ranges from 1×10⁶ to 1×10⁹ CFU/g feed. Lower concentrations may not deliver clear benefits, while higher doses give diminishing returns. Second, it is best to avoid simultaneous use with therapeutic antibiotics, which can impair spore germination and colonisation – a gap of at least 36 hours is advisable. Third, different strains vary considerably in function. When purchasing, check the viable count and, more importantly, the strain identification, and choose one that matches your specific need, whether for necrotic enteritis control or late‑lay egg quality improvement.

      Lowering feed costs, reducing medication expenses and improving air quality inside the house – doing all three well at the same time is no small task. But Bacillus subtilis, at least for now, appears to be a path worth serious consideration.