Bile Acids for Weaned Piglets: Permitted Doses and Evidence

Bile acids are a permitted feed additive in China for weaned piglets, at a recommended inclusion of 80 to 100 mg/kg and a maximum limit of 100 mg/kg, calculated on a feed basis of 88% dry matter. That figure comes from Ministry of Agriculture and Rural Affairs Announcement No. 257, which extended the permitted use of bile acids to weaned piglets and freshwater fish.

For a formulator or buyer, the useful question is not whether bile acids are allowed — they are — but what the permitted dose means, what the published trials measured at and around it, and how to specify the product so that what arrives matches what the trial used. This article covers the regulatory position, the trial evidence and the product parameters that matter for a feed application. It is about use in animal feed and makes no claim about human use.

What “bile acids” means as a feed additive

In feed regulation, “bile acids” is a product category, not a single molecule. The category covers bile-acid material recovered from animal bile and prepared to a feed-grade specification. It is a multi-component mixture rather than one purified substance, which is why its specification is written around a content figure and a set of physical parameters rather than a single assay of one compound.

The distinction from a pharmaceutical-grade bile acid is worth holding on to. A purified ursodeoxycholic acid or chenodeoxycholic acid is judged against a pharmacopoeial monograph. A feed-grade bile acid preparation is judged against a feed additive specification and the rules on permitted use. They are different products, sold against different standards, and a specification sheet should make clear which one it describes.

The regulatory position: what is permitted, and for which species

Bile acids entered the Chinese feed additive catalogue for specific species, and the permitted list has been extended by successive announcements. The relevant milestones are:

Two things follow from reading the list as a whole. First, the inclusion limits are set per species, and they are not transferable — the piglet limit is much lower than the carnivorous-fish limit, and using one product at another species' rate is not what the approval covers. Second, the category is still being extended, so the current version of the catalogue and the announcements should be checked rather than relied on from memory. Announcements after a given date can change the permitted species and the limits.

The permitted dose for weaned piglets

For weaned piglets, the permitted figures are specific and narrow:

The basis line matters as much as the number. “mg/kg, on a feed basis of 88% dry matter” is a defined reference point; a dose quoted simply as “mg/kg” against a different moisture basis is a different quantity of active material. For anything sold into a regulated feed market, stating the basis is part of stating the dose.

Note also the shape of the range. The recommended band and the maximum limit are close together — 100 mg/kg is both the top of the recommendation and the ceiling. This is not a species where a formulator has room to work well above the permitted band; the regulatory question and the formulation question converge at the same number.

What the published trials measured

Independent of the regulation, a body of controlled trials has looked at bile-acid supplementation in weaned pigs. The dosages and the measured outcomes are worth reading together, because they show what was actually tested.

The consistent finding across these trials is the one most relevant to a buyer: the measured effect is on growth and nutrient utilisation, and the work sits around a dose band rather than a single magic number. Cao et al. proposed around 100 mg/kg as the working dose, which is at the top of the permitted Chinese range — and the higher doses in the later studies sit well above the current permitted ceiling for this species, which is the gap between a research setting and a regulated feed product.

Reading trial doses against permitted doses
A dose that appears in a research paper is not automatically a permitted dose. Trials are run to test effects, and several of the piglet studies used levels above the 100 mg/kg ceiling set for commercial feed. When a supplement is specified for a regulated market, the permitted limit is the constraint, and the trial literature is background rather than a licence.

One further point belongs here. These are production outcomes in pigs — growth, feed utilisation, intestinal measures — reported from controlled animal trials. They are not, and are not presented as, statements about human use of any bile acid.

Why weaned piglets are the point of application

The timing of the permitted use reflects the biology of weaning rather than a marketing choice. A piglet at weaning moves from a liquid, fat-rich diet to a solid, plant-based one, and its digestive and absorptive capacity is still maturing. Fat digestion in particular depends on bile-acid-mediated emulsification, and the piglet's own bile output is still developing at that stage.

That is the rationale for supplementation at weaning: supplying bile acids exogenously during the window when endogenous supply is limiting, to support the digestion and absorption of dietary fat. It is also why the application is defined for the post-weaning period specifically, and why the permitted species list distinguishes weaned piglets rather than pigs in general.

Product form, and what to specify

As a multi-component feed ingredient, a bile-acid supplement is specified differently from a purified pharmaceutical. The parameters that matter for a feed application are:

• Content / active figure. The declared content of bile acids, and the method by which it is determined. Because the category is a mixture, “content” needs a defined basis — which acids, and by which analytical method.
• Form and handling. Whether the product is a powder or a liquid, and whether it is carrier-based. Feed mills add small quantities, so flowability, dusting and mixing behaviour matter as much as the chemistry.
• Animal-source documentation. As with any animal-derived ingredient, the species of origin and the traceability record should be available, because a feed purchaser needs them for the finished-feed dossier.
• Stability in the feed. How the active content holds through mixing, storage and, where relevant, pelleting.
• Compatibility with the permitted limit. The specification should make it possible to hit the 80–100 mg/kg band accurately at practical inclusion rates.

The documentation chain for an animal-derived bile material is the same one that applies to the dried bile powder used as a raw material, which the Chinese Pharmacopoeia describes directly; that monograph and its animal-source checks are set out in dried pig bile powder under the Chinese Pharmacopoeia. The general discipline of checking a supplier against its own documents is in how to verify a bile-acid supplier.

Questions buyers ask

Are bile acids allowed in piglet feed in China?
Yes. MARA Announcement No. 257 (2020) extended permitted use to weaned piglets, with a recommended inclusion of 80–100 mg/kg and a maximum limit of 100 mg/kg.

What is the maximum permitted dose?
100 mg/kg complete feed, on a feed basis of 88% dry matter.

What did the trials measure?
Growth performance and nutrient digestibility, along with intestinal measures. Cao et al. (2021) reported improved average daily gain and greater nutrient digestibility, and proposed about 100 mg/kg as a working dose.

Is the piglet dose the same as for fish?
No. The inclusion limits are set per species and are not transferable; the freshwater fish range, for example, is 20–60 mg/kg.

Why is the application specific to weaned piglets?
Because fat digestion depends on bile-acid emulsification and the piglet's own bile output is still maturing at weaning, so the post-weaning window is where supplementation is applied.

What should a feed-grade bile acid specification state?
The declared content and its analytical basis, the form and carrier, stability in feed, and the animal-source and traceability documentation — in addition to the permitted use and limit.

What to ask a supplier

For a feed application, the questions split cleanly between the product and the paperwork, and both need answers.

On the product: ask for the declared content and how it is analysed, since the category is a mixture; ask for the form, carrier and flowability data, because the additive is used at low inclusion; and ask for stability data in the finished feed. On the paperwork: ask for the species of origin and the traceability record, because the feed dossier needs them. And confirm the permitted use and limit for the target species from the current catalogue and announcements rather than from a supplier's summary.

Our bile-acid range is described with the parameters buyers ask about most, and you can request a quotation against your own acceptance criteria.

The permitted use and limits quoted here come from the Ministry of Agriculture and Rural Affairs of China, whose register is published on Chinese government infrastructure and is not linked here. The comparable European framework sits in Regulation (EC) No 1831/2003 on feed additives. The trial data are from peer-reviewed animal-nutrition research — Cao et al. (2021) and Zhang et al. (2025) — where the full methods and results can be read.

This article describes feed-additive regulation, product specification and published animal-nutrition research. It concerns use in animal feed only and makes no statement about human use, and it does not set out commercial guarantees. Always check the current permitted use and limits for your market before formulating.

Frequently asked questions

Are bile acids permitted as feed additives?

Permission attaches to a specific substance with a specific claimed function in a specific market, not to "bile acids" as a family. Some markets authorise individual compounds under their feed additive rules; others treat them differently. The buyer's first document is the authorisation or catalogue reference for the exact substance, not a supplier brochure.

Does feed grade differ from API grade?

In documentation and limits, not in identity. Feed files emphasise the panels the feed law cares about, such as heavy metals and contaminants, together with the approved function. A material can carry a clean pharmaceutical-style COA and still lack the feed documentation a destination market requires. The two documents answer different questions.

Why is the dose question a regulatory question rather than a nutrition one?

Because inclusion rates come from the authorisation, not from the supplier. A supplier who quotes doses outside the authorised range is transferring the compliance risk to the feed producer. Ask for the authorised range with its reference before discussing anything that looks like a feeding recommendation.

What documentation should a feed producer request with the first order?

A specification, a COA against that specification, an origin statement, and the authorisation or catalogue reference for the substance in the destination market. For an animal-derived product, add the traceability documents that connect the batch to its source. Each of these is cheap before the order and expensive after it.

Where do supplier specifications usually differ most?

In the impurity table. Two specifications can carry an identical assay figure while one names four impurities with individual limits and the other names none. For a feed application the contaminant panel matters the same way: what is tested says more than what is claimed.

Can a sample be evaluated without full registration?

Research and development use is usually possible under the buyer's own controls, but activities that shade into production feeding may already fall under feed law. The line differs by market. Confirm which activities the exemption covers before running a field trial, because a trial that breaks the rules contaminates the registration case it was meant to support.