What taurine is
Taurine is 2-aminoethanesulfonic acid — technically a sulfonic acid rather than a true amino acid, since it carries a sulfonate group in place of the typical carboxyl group. It is found at high concentration in skeletal muscle, heart, retina, and brain. Animals synthesize taurine from cysteine and methionine via the cysteine sulfinic acid pathway, but the synthesis rate varies dramatically by species. Cats are the textbook case for low endogenous synthesis; dogs sit in the middle; rodents and primates synthesize freely.
Why cats are the strict case
Per the Hayes, Carey, and Schmidt 1975 paper in Science, cats fed a casein-based protein source developed retinal degeneration linked to a selective decrease in plasma and retinal taurine concentrations. The discovery established taurine as a dietary essential for cats and reshaped commercial cat-food formulation through the late 1970s and 1980s. Per the Pion et al. 1987 paper in Science, taurine deficiency was then identified as the cause of the feline dilated-cardiomyopathy epidemic of the 1980s — a finding that triggered AAFCO to add taurine to the Cat Food Nutrient Profiles in 1989.
Two physiological quirks make cats dependent on dietary taurine. First, cats have low cysteine sulfinic acid decarboxylase activity, so they synthesize less taurine from precursors than most mammals. Second, cats conjugate bile acids exclusively with taurine, while dogs and humans use both taurine and glycine. Bile-acid conjugation is an obligate, daily loss; cats cannot fall back on glycine when taurine runs short. The result: taurine is a true essential nutrient in feline diets.
The dog story is more complicated
Dogs synthesize taurine from cysteine and methionine and conjugate bile acids with both taurine and glycine, so AAFCO does not list taurine as essential in the Dog Food Nutrient Profiles. But certain breeds — Golden Retrievers, Newfoundlands, American Cocker Spaniels, English Setters — show measurably lower plasma taurine and a documented predisposition to dilated cardiomyopathy that responds to taurine supplementation (Backus et al. 2003, Journal of Nutrition; Kaplan et al. 2018, PLOS ONE).
The FDA-CVM 2018-2022 investigation into a potential link between diet and canine dilated cardiomyopathy ran for four and a half years before pausing public updates in December 2022. The agency did not establish a causal link between any single ingredient and DCM. The investigation focused on grain-free diets containing peas, lentils, other legume seeds, and potatoes — the so-called BEG (boutique, exotic-ingredient, grain-free) diets. Some affected dogs had low plasma taurine; others had normal taurine and DCM regardless. The biological mechanism remains unsettled. Per the AVMA 2022 statement, FDA paused additional updates pending more definitive science.
The MDPI 2024 narrative review (PMC12656978) and the 18-month prospective study published in 2025 (PMC12408985) found no echocardiographic differences between dogs fed grain-free vs. grain-inclusive diets, with whole blood and plasma taurine remaining within normal ranges in both groups. A higher prevalence of premature ventricular contractions was observed in dogs on FDA-listed-ingredient diets (10% vs 2%), but the clinical significance is unclear.
How taurine appears on the label
If a pet food adds taurine, it appears in the ingredient list as “taurine.” In cat food carrying a complete-and-balanced AAFCO statement, taurine inclusion is mandatory and the level is verified through either formulation analysis or a feeding trial under the AAFCO Procedures for Conducting Pet Food Feeding Trials (which specifically include blood-taurine measurement for cats). In dog food, taurine is optional. Some manufacturers add it explicitly to large-breed or grain-free formulas as an at-risk-breed precaution; others rely on the methionine-cysteine content of high-quality animal protein to support endogenous synthesis.
What KibbleIQ does with this
Under the KibbleIQ Cat Food Rubric, declared taurine inclusion is an AAFCO floor, not a positive differentiator — we expect every complete-and-balanced cat food to meet the 0.1% / 0.2% minimum. We flag a cat food that omits taurine entirely or relies on a label disclaimer (“for intermittent feeding”) since this signals an incomplete formulation. Under the Dog Food Rubric, supplemental taurine in grain-free or legume-heavy formulas earns a small positive note as a defensive measure given the FDA-CVM 2018 signal, but we do not penalize standard grain-inclusive dog food for omitting it. Foods using high-quality muscle meat as the first ingredient (chicken, salmon, beef) supply ample methionine-cysteine substrate for endogenous synthesis in healthy dogs of unaffected breeds.
Bottom line
If you feed cats: confirm the AAFCO statement says “complete and balanced” for the relevant life stage and verify taurine appears in the ingredient list. Per AAFCO Cat Food Nutrient Profiles, every commercial complete-and-balanced cat food should meet the 0.1% / 0.2% minimum — if you see “intermittent feeding” on the bag, choose another food. If you feed at-risk breeds (Golden Retriever, Newfoundland, Cocker Spaniel, Doberman, Boxer), the WSAVA 2018 Global Nutrition Guidelines recommend baseline plasma and whole-blood taurine measurement before transitioning to a grain-free or BEG-style diet, and your vet should re-check at 6-12 months.
For breed-specific risk profiles, see our guides on Golden Retrievers, Dobermans with heart disease, and large-breed dogs. For brand-by-brand AAFCO substantiation under the FDA-CVM grain-free signal, see Purina Pro Plan (grain-inclusive, feeding-trial substantiated).