Dogs live longer now as they eat balanced nutrition and spend more time in safe environments, as opposed to roaming the neighborhood and eating scraps. Those older dogs have different nutritional needs, but formulations designed for them may be based more in marketing than science, Claire Timlin, Ph.D., director of research and development at Four Rivers Kennel, said during her presentation at Petfood Forum 2025.
Emerging evidence suggests that existing amino acid guidelines established by the National Research Council and the Association of American Feed Control Officials may be outdated and insufficient for meeting the diverse nutritional needs of modern pet dog populations, she said.
“Dogs have an amino acid requirement, not necessarily a protein requirement,” Timlin said. “High protein foods are not really doing any good if we are not fulfilling those [limiting amino acid] requirements.”
“We see a lot of marketing out there for senior specialized diets, but not a lot of research focusing on actual requirements for senior dogs,” she said.
Currently, both AAFCO and NRC offer recommendations focused exclusively on two life stages: growth/reproduction and adult maintenance. These guidelines largely overlook senior dogs, whose metabolic profiles and digestive efficiency differ significantly, she said.
“Senior dogs represent an increasing percentage of the pet population,” Timlin said. “They are losing lean mass, have less digestibility and reduced feed intake.”
Most data underpinning these standards come from older methodologies such as nitrogen balance tests, and from limited breed and size models. In contrast, Timlin’s team utilizes the Indicator Amino Acid Oxidation (IAAO) technique, which measures amino acid metabolism via breath analysis. Though expensive and logistically complex, the IAAO method delivers more accurate insights into amino acid utilization across breeds, life stages and dietary compositions.
In one example from Timlin’s research, methionine requirements determined by IAAO for puppies, adults and seniors exceeded NRC minimums. The IAAO-derived recommended allowances for total sulfur amino acids also highlighted life-stage-specific variations, showing decreases in senior dogs as expected, but also a rebound in requirements when accounting for lean mass loss.
Dog food digestibility doesn’t equal bioavailability
Timlin highlighted the distinction between digestibility and bioavailability.
“Digestibility is the ability for the dog to uptake amino acid in the small intestine,” she said. “Bioavailability means the body can then use it.”
For instance, despite expectations, a study found pea protein had higher methionine bioavailability than chicken meal, she said.
Metabolic availability can vary significantly among ingredients due to processing, cooking, or the raw material itself. Data compiled from both human and canine studies demonstrated how ingredients like soy protein isolate and casein are relatively bioavailable, while others like chickpeas and certain rendered meals are less so.
Timlin emphasized that overformulating diets, a common industry practice intended to ensure adequacy, may lead to unnecessary nitrogen loads, particularly harmful to senior animals with impaired renal and hepatic function. She called for more targeted formulation to improve sustainability and reduce waste.
She also cautioned against overgeneralizing nutritional data across breeds.
“In livestock, we have created genetically uniform animals, so precision feeding works well. In pet food, we have diverse breeds with different needs,” she said.
Likewise, although formulations aimed at senior dogs are common, those recipes may not have scientific backing.
“We see a lot of marketing out there for senior specialized diets, but not a lot of research focusing on actual requirements for senior dogs,” she said.
To close the research gap, Timlin urged the pet food industry to increase funding for unbiased, broad-spectrum nutritional studies.
“Unlike livestock, pet food research can’t be funded by the USDA or other NIH sources all the time,” she said. “It’s imperative that the pet food industry comes together and creates more funding opportunities.”