Broiler study questions TiO2’s neutrality as a feed marker

Titanium dioxide has long been treated as a practical, inert marker in poultry digestibility work, but a new broiler study is challenging that assumption. In a preprint posted May 20, 2026, researchers reported that dietary TiO2 altered intestinal fermentation patterns and microbial composition in broilers, even though it did not change growth performance or organ development over a 32-day feeding period. The findings add fresh evidence that TiO2 may not be biologically neutral in studies that measure gut function. (preprints.org)

That matters because TiO2 already sits in a complicated regulatory position. EFSA said in 2021 that titanium dioxide could no longer be considered safe as a feed additive, citing unresolved genotoxicity concerns, low absorption but possible accumulation, and insufficient data to conclude on safety for animals, consumers, and the environment. The European Commission then denied authorization for TiO2 as a feed additive and required existing additive stocks to be withdrawn by March 20, 2022, followed by feed materials and compound feed by June 20, 2022. (efsa.europa.eu)

Even with that regulatory backdrop, TiO2 has remained scientifically relevant because of its widespread historic use in digestibility trials. Earlier poultry literature described TiO2 as a common marker, typically used at inclusion levels around 0.1% to 0.5%, and one 2023 PLOS One paper noted it remained a marker of choice in many feeding trials because it is easy to measure and had been viewed as lower risk than chromium-based markers. That same paper, however, also acknowledged that different markers can yield different digestibility estimates and may have matrix- or gut segment-specific interactions. (journals.plos.org)

In the new study, the authors combined ex vivo fermentation systems with an in vivo broiler trial to test TiO2 at 4 kg/ton feed, a level they described as typical for animal nutrition studies. Ex vivo, TiO2 reduced gas production and acetic acid in the ileum, while increasing gas production, total eubacterial counts, and branched-chain fatty acids in the caecum. In vivo, TiO2 increased caecal isobutyric acid and total branched-chain fatty acids, and shotgun metagenomics showed higher caecal Shannon diversity plus enrichment of taxa associated with amino acid metabolism, including Massilicoli timonensis, Blautia merdavium, Rubneribacter badeniensis, and Mediterraneibacter caccavium. The authors concluded that dietary markers may not be biologically inert. (preprints.org)

There doesn’t appear to be a separate institutional press release or broad industry reaction yet, which is not unusual for a newly posted preprint. Still, the paper lands alongside a 2025 RIVM risk assessment commissioned after requests for exemptions to use TiO2 as a research marker in feed. RIVM concluded that for short-living farm animals such as broilers, harmful effects could not be excluded but the risk was expected to be low, while uncertainty remained for consumers eating products from animals exposed to TiO2 in feed. That assessment doesn’t validate the new broiler findings directly, but it does reinforce that TiO2’s research use remains under scrutiny. (rivm.nl)

Why it matters: For veterinary professionals, nutritionists, and poultry researchers, the practical issue is less about immediate flock performance and more about study interpretation. If TiO2 changes fermentation endpoints, microbial diversity, or amino acid metabolism, then trials using it as a marker may be introducing a confounder when the outcome of interest is gut health, microbiome composition, or nutrient utilization. That’s especially relevant in work on enzymes, prebiotics, fiber, and feed additives, where relatively modest microbial shifts can shape conclusions. The current paper is a preprint, so its methods and conclusions still need peer review, but it raises a credible caution flag. (preprints.org)

There’s also a broader research design question. Some earlier work found no meaningful TiO2 effect on recovery of inositol phosphates in broiler digesta, suggesting the marker may be fit for purpose in some narrowly defined applications. The emerging picture is not that every TiO2-based study is invalid, but that its effects may depend on the biological endpoint, diet matrix, and gut segment being measured. That’s a more nuanced message than “safe” or “unsafe,” and it’s likely the one veterinary readers will need as they evaluate older literature and plan new studies. (journals.plos.org)

What to watch: The next steps are peer review, possible publication in a final journal version, and whether researchers or regulators move toward clearer guidance on when TiO2 can still be justified as a research marker, and when alternative markers may be preferable. (preprints.org)