Bioavailability is the percentage of an ingredient that actually reaches your horse’s bloodstream and target tissue after digestion. Two supplements can list the same ingredient at the same dose, but deliver vastly different amounts to the joint — the chemical form, source, and molecular size determine how much your horse absorbs versus how much passes through as waste.
The milligrams on the label are not the milligrams your horse’s joints receive. That gap between “what’s in the scoop” and “what gets absorbed” is bioavailability, and it’s the single most misunderstood number in equine supplementation.
Why the Chemical Form Matters More Than the Dose
Take zinc. Three forms show up on supplement labels: zinc methionine (chelated), zinc sulfate, and zinc oxide. All three are “zinc.” But zinc methionine binds the mineral to an amino acid, which tricks the gut into absorbing it through amino acid transport channels rather than competing with other minerals for limited absorption sites. Zinc oxide sits at the bottom — the cheapest to manufacture, the hardest for your horse to use.
The same pattern repeats across the ingredient list. Glucosamine HCl delivers more active glucosamine per milligram than glucosamine sulfate because the hydrochloride salt has a higher glucosamine content by weight. Sodium hyaluronate absorbs better than generic “hyaluronic acid” because the sodium salt form is smaller and more soluble. Orthosilicic acid is bioavailable silica; colloidal silica mostly isn’t.
This is why we score Ingredient Form as a separate dimension in every audit. A product can hit the right dose on paper and still underdeliver if the forms are wrong.
A Real Example From Our Database
Flex+Max and FluidFlex both contain glucosamine HCl from shellfish — same form, same source. But Flex+Max delivers 10,000 mg per serving and FluidFlex delivers 5,000 mg. Even with identical bioavailability, your horse absorbs twice as much glucosamine from Flex+Max. Form sets the absorption rate. Dose sets the total absorbed.
Now compare Cosequin ASU and KPP Joint Armor. Both contain chondroitin sulfate at 1,200 mg. But Flex+Max’s label specifies low molecular weight chondroitin (porcine source), which means a smaller molecule that crosses the intestinal wall more easily. Joint Armor lists chondroitin sulfate without specifying molecular weight. Same dose, potentially different absorption. The label tells you one number; your horse’s gut decides another.
What You Can Control
- Pick chelated minerals over oxides. Zinc methionine over zinc oxide. Copper lysine over copper sulfate. Manganese proteinate over manganese oxide. The price difference is small; the absorption difference is not.
- Look for named forms on the label. “OptiMSM” tells you more than “MSM.” “FCHG49” on Cosequin’s glucosamine means a published specification with batch-level quality control. Generic names aren’t necessarily bad, but named specs mean someone is tracking purity.
- Don’t confuse more ingredients with more absorption. A product with 12 ingredients at trace doses may deliver less to your horse’s joints than a product with 4 ingredients at full dose in optimal form. The label is a list. Bioavailability decides what actually counts.
We built the Ingredient Form dimension into our scoring rubric because bioavailability separates products that work from products that look like they should work. Every audit report breaks down the form score for each ingredient — check any audit in our database to see how the product you’re feeding stacks up.
Frequently Asked Questions
Can I improve bioavailability by feeding supplements with grain?
Feeding with a meal can help. Fat in the feed improves absorption of fat-soluble compounds, and the digestive enzymes triggered by eating aid breakdown of supplement ingredients. Don’t feed joint supplements on an empty stomach if you can avoid it.
Is liquid or pellet form more bioavailable?
Liquid supplements skip the dissolution step that pellets require, which can speed absorption slightly. But the chemical form of the active ingredient matters far more than the delivery format. A pellet with glucosamine HCl at 10,000 mg will outperform a liquid with 5,000 mg every time, regardless of how fast the liquid absorbs.