Polystyrene Microplastics in Poultry: 0.5 mg/d Damages Gut
A 120-day feeding study on Chahua chicken No. 2, an indigenous Chinese breed, shows that polystyrene microplastics in poultry drinking water at 0.5 mg per day cut growth, worsened feed conversion, and rewired the gut barrier, inflammatory signals, and microbial community. Lower doses left growth intact but still shifted gut genes.
Quick answer
Polystyrene microplastics in poultry are not a future worry. In a 120-day trial, 0.5 mg per day of polystyrene microplastics in drinking water reduced body weight, average daily gain, and feed intake in Chahua chicken No. 2 at both 42 and 120 days, and pushed feed conversion toward worse at 120 days. The same dose weakened the intestinal barrier, raised inflammatory cytokines, and shifted the gut microbiota. Lower doses spared growth but still changed gut gene expression.
Why polystyrene microplastics in poultry deserve attention
Microplastics are now found across freshwater, soil, and marine systems, and polystyrene is among the most common types because it is cheap, widespread, and detected often in the environment. Chickens drink from water that can carry these particles, and the gut is the first site they hit. The avian intestine differs from fish and mammal guts in structure and function, so toxicity seen in those animals does not automatically transfer to birds.
Most published work on microplastic gut damage comes from fish and mice. Poultry, especially indigenous breeds raised for meat quality, has far fewer direct studies. That gap matters for producers because gut barrier health, inflammation, and the microbial community sit at the center of growth, feed efficiency, and disease resistance. A finding in one species does not tell a farm what to expect in its flock.
How the trial was built
The study used Chahua chicken No. 2, a native Chinese chicken valued for meat quality. Birds were split into four drinking-water treatments and tracked for 120 days.
| Element | Detail |
|---|---|
| Breed | Chahua chicken No. 2, an indigenous Chinese meat-type chicken |
| Groups | CON (0 mg/d), 0.05 mg/d, 0.1 mg/d, 0.5 mg/d polystyrene microplastics |
| Route | Drinking water, daily |
| Particle | Polystyrene microspheres, greater than 99 percent pure, uniform size, green-fluorescent |
| Brooding | Days 1 to 21 at 32 to 35 degrees Celsius, then 2 to 3 degrees Celsius lower per week to 22 degrees Celsius; relative humidity 60 to 65 percent |
| Replicates | Three independent experimental replicates per treatment for morphology, gene, and microbiome work |
| Microbiome | 16S rRNA gene sequencing, SILVA database version 138.2, confidence threshold 0.7 |
The microplastic particles were verified as pure polystyrene with a uniform size distribution by the supplier. Green fluorescence let the team trace where particles lodged in the gut wall under a microscope.
What the growth data showed
The highest dose did the clear damage. At 0.5 mg per day, body weight, average daily gain, and feed intake were all significantly lower than the control at 42 days and again at 120 days. At 120 days the feed conversion ratio trended worse in the 0.5 mg per day group, with a p value of 0.058, just outside the strict significance line but pointing the same direction.
| Dose | Body weight, gain, feed intake | Feed conversion | Carcass notes |
|---|---|---|---|
| 0.5 mg/d | Lower at 42 and 120 days, p less than 0.05 | Tendency worse at 120 days, p = 0.058 | Lower semi-eviscerated and eviscerated yield, breast and thigh muscle weights at 42 days, p less than 0.05 |
| 0.1 mg/d | No growth effect | No effect | Lower ileal villus height, p less than 0.05 |
| 0.05 mg/d | No growth effect | No effect | No growth effect |
Lower doses, 0.05 and 0.1 mg per day, did not move growth performance. That separation is useful: it tells producers the growth hit is dose-dependent and that a threshold exists somewhere below 0.5 mg per day, at least in this breed and over this period.
The gut wall took the hit first
Intestinal morphology worsened with dose. At 0.5 mg per day, jejunum villus height and the villus height to crypt depth ratio fell, and crypts deepened, all at p less than 0.05. The ileum showed the same pattern. At 0.1 mg per day, ileal villus height alone dropped significantly, showing that structural harm begins before growth itself suffers.
Fluorescent signal confirmed the particles were present. The 0.5 mg per day group showed significantly higher green-fluorescence intensity in both jejunum and ileum than the control, a dose-dependent pattern that links the physical presence of particles to the tissue changes.
Barrier genes and inflammatory cytokines shifted
Gene expression told the mechanism story. At 0.5 mg per day, intestinal barrier genes dropped, with ZO-1 and Claudin-1 reaching significance at p less than 0.05. Tight junction proteins are what keep the gut lining sealed, so their loss points to a leakier wall.
| Process | Genes | Direction |
|---|---|---|
| Barrier integrity | ZO-1, Occludin, Claudin-1 | Downregulated, ZO-1 and Claudin-1 significant at p less than 0.05 |
| Inflammation | IL-6, IL-8, IL-1beta, TNF-alpha, MIP-1beta | Upregulated, p less than 0.05 |
| Glucose transport | SLC5A1, SLC2A2 | Downregulated, p less than 0.05 |
| Lipid transport | SLC27A4, APOA1, APOB, MTTP, CD36, FABP2 | Downregulated, p less than 0.05 |
| Amino acid transport | SLC15A1, SLC7A1, SLC7A9, SLC3A1, SLC6A19 | Downregulated, p less than 0.05 |
Inflammatory cytokines rose across the board: IL-6, IL-8, IL-1beta, TNF-alpha, and MIP-1beta all increased at p less than 0.05. The study also found that nutrient transporter genes for glucose, lipid, and amino acid uptake were suppressed at the same dose. A weaker barrier plus more inflammation plus fewer transporters is a coherent picture: the gut absorbs less and defends worse.
The microbial community moved too
The 0.5 mg per day dose reshaped the gut microbiota. Several taxa rose in relative abundance at p less than 0.05: norank_o_Clostridia_UCG-014, Mediterraneibacter, Olsenella, and Faecalitalea. At the phylum level, Bacteroidota was higher in the 0.5 mg per day group than in the lower-dose groups, and Patescibacteria was higher than the control.
Alpha diversity told a subtler story. The Ace, Chao, and Sobs indices of the 0.5 mg per day group were significantly higher than the 0.05 mg per day group at p less than 0.05, while principal coordinate analysis separated the groups clearly at p less than 0.05. Lower doses also left their mark: the 0.05 mg per day group showed higher Lactobacillus and Limosilactobacillus than control and high-dose groups, and the 0.5 mg per day group showed higher Anaerobutyricum and norank_o_RF39 than the two middle doses.
The counterintuitive part: low doses are not harmless
The easy read is that only 0.5 mg per day matters because only that dose cut growth. The data push back. At 0.05 and 0.1 mg per day, barrier and inflammatory genes still changed, and the ileal microbiota shifted, even though the birds grew normally. Growth performance is a blunt instrument; gut gene expression is a finer one. A farm watching only weight gain would miss early gut stress that a higher dose later turns into lost performance.
This is the practical twist for anyone judging microplastic risk in feed or water. Waiting for a growth drop before acting means waiting until damage is already established. The gene and microbe signals at low doses are the earlier warning light.
What this means for poultry producers
Three steps follow from the work.
- Test drinking water and feed for microplastic load rather than assuming it is zero, since the gut is the entry point and the dose here entered through water.
- Treat gut barrier and inflammatory gene markers, not just weight, as the health signal worth watching in indigenous breeds where meat quality depends on gut state.
- Keep a margin below the levels shown to harm growth; the study suggests the trouble line for this breed sits near 0.5 mg per day, with lower doses already shifting gut biology.
Limitations to keep in view
The work used one indigenous breed, Chahua chicken No. 2, over 120 days, so the exact dose threshold may differ in faster-growing broilers or other breeds. The particles were pure, fresh polystyrene rather than aged or weathered plastic, which behaves differently in the gut. The 16S rRNA method describes community composition but not microbial function or metabolites, so the link from shifted taxa to the barrier and transport changes is association, not proven cause. The authors call for aged-particle and functional studies to confirm the path.
Bottom line
Polystyrene microplastics in poultry drinking water at 0.5 mg per day damaged growth, feed conversion, gut structure, barrier genes, inflammatory signals, and the microbial community in Chahua chicken No. 2 over 120 days. Lower doses spared growth yet still moved gut genes and microbiota. The takeaway for producers is to monitor microplastic exposure early, because the gut biology shifts before the scale does.
FAQ
What did 0.5 mg/d of microplastics do to the chickens?
At 0.5 mg per day, body weight, average daily gain, and feed intake fell at both 42 and 120 days at p less than 0.05. Feed conversion trended worse at 120 days with p = 0.058. Carcass yields and breast and thigh muscle weights were also lower at 42 days. The dose clearly reduced growth and slaughter value in this breed.
Do lower microplastic doses harm chickens at all?
Lower doses of 0.05 and 0.1 mg per day did not change growth performance in the trial. They did shift intestinal barrier and inflammatory gene expression and alter the ileal microbiota at p less than 0.05. Growth is a blunt gauge, so gut biology moved before weight did, and low doses are not harmless.
How did the microplastics damage the gut wall?
The 0.5 mg per day dose lowered jejunum and ileum villus height and the villus to crypt ratio, and deepened crypts, all at p less than 0.05. Barrier genes ZO-1 and Claudin-1 dropped, and green fluorescence confirmed particles lodged in the gut wall. The result is a thinner, leakier intestinal lining.
Which inflammatory signals went up with exposure?
IL-6, IL-8, IL-1beta, TNF-alpha, and MIP-1beta all rose at p less than 0.05 in the 0.5 mg per day group. These cytokines mark gut inflammation and recruit immune cells to the tissue. Their increase sat alongside dropped barrier genes and suppressed nutrient transporter genes, a coherent picture of a stressed, less absorptive gut.
What happened to the gut microbes?
The 0.5 mg per day group showed higher norank_o_Clostridia_UCG-014, Mediterraneibacter, Olsenella, and Faecalitalea at p less than 0.05, plus higher Bacteroidota and Patescibacteria. Alpha diversity indices rose versus the 0.05 mg per day group, and principal coordinate analysis separated the groups at p less than 0.05.
Were nutrient absorption genes affected?
Yes. At 0.5 mg per day, glucose transporters SLC5A1 and SLC2A2, lipid transporters including CD36 and FABP2, and amino acid transporters including SLC15A1 and SLC7A1 were all downregulated at p less than 0.05. Fewer transporters mean less uptake of energy, fat, and protein building blocks from feed.
Does this apply to fast-growing broilers?
Not directly. The study used Chahua chicken No. 2, a native meat breed, for 120 days, and the harm threshold may differ in commercial broilers. The mechanism, gut barrier and microbial disruption, is likely shared across birds, but the exact dose that cuts growth should be re-tested per breed and diet.
How were the microplastics given to the birds?
Particles entered through drinking water every day at 0, 0.05, 0.1, or 0.5 mg per day. They were pure polystyrene microspheres, over 99 percent pure with uniform size and green fluorescence for tracing. Birds were reared under standard brooding heat and humidity before the 120-day measurement window.
Is the damage proven to be caused by the particles?
The work shows strong association, not proven cause. The 16S rRNA method maps community makeup but not function or metabolites, and correlation between taxa and gene expression did not survive multiple-test correction. The authors frame the results as a call for functional and aged-particle studies to confirm mechanism.
What should a farm do about microplastics?
Monitor microplastic load in drinking water and feed, since the gut is the entry point and exposure here came through water. Watch barrier and inflammatory gene or metabolite markers, not only weight, in breeds where meat quality tracks gut health. Keep exposure well below the levels shown to cut growth, near 0.5 mg per day in this study.
Why study an indigenous chicken breed?
Indigenous breeds like Chahua chicken No. 2 are raised for meat quality, and their gut state drives that quality, yet they are under-studied for microplastic effects. Most gut-toxicity data come from fish and mice. Testing a native bird closes a real gap and gives producers of quality breeds a direct evidence base.
How long did the chicken study run?
The trial ran 120 days, with gut morphology, gene expression, and microbiome measured at 42 days and growth and feed conversion tracked through to 120 days. The brooding phase was days 1 to 21 under controlled heat and humidity before the main measurement period began. Sampling at two time points let the team separate early gut changes from later growth loss.
