Use of these testing procedures has shown that aged dogs are on average, able to learn simple associative tasks such as visual
discrimination (learning that one of two different objects covers a food reward), at the same level as younger dogs. Significant
impairment is seen, however, on more complex discrimination learning problems, such as when the objects become increasingly
similar or in reversal tasks, where the pet first learns under which object the food is located and then must learn that the
reward has been moved to the previously unrewarded object.
In addition to learning ability, memory is also compromised in aged dogs.
Aged dogs seem to fall into one of three categories based on learning and memory testing: (1) unimpaired or successful agers;
(2) age-impaired; (3) severely impaired. These clusters of aged dogs may be analagous to declines along a "cognitive continuum"
in people with mild age-associated memory impairment followed by cognitive decline and dementia.
The decline in learning and memory documented in laboratory studies to arise as early as 6 to 7 years of age is consistent
with behavioral changes observed in dogs with CDS.
Careful questioning of the owner is the best way for veterinarians to detect early signs of cognitive impairment, since many
of the early signs are subtle and might otherwise not be reported. A questionnaire is a useful diagnostic tool and an excellent
means of tracking changes and response to therapy (Table 1).
Table 1: Behaviors evaluated in dogs to assess age-related cognitive decline*
A series of studies were initiated to test the hypothesis that a food enriched with complex mixtures of antioxidants and mitochondrial
cofactors could result in improvements in learning and memory and reduce the extent of pathology that accumulates in aged
A longitudinal investigation of the effects of dietary management on cognitive function of Beagles has recently been completed.
The experimental subjects are groups of aged Beagle dogs (10 to 13 years old) and young dogs (3 to 5 years old). The study
was conducted as a randomized controlled clinical trial with each animal assigned to an extruded senior dog food (control)
or an enriched food. No differences in cognitive ability existed between groups prior to dietary intervention
The enriched food was supplemented with Vitamins E and C, a mixture of fruits and vegetables rich in carotenoids and flavonoids
and mitochondrial cofactors (L-carnitine, dl-α-lipoic acid). Vitamin E is a lipid-soluble vitamin that protects cell membranes
from oxidative damage, while vitamin C is a water-soluble vitamin that helps replenish vitamin E cellular levels. L-carnitine
is a precursor to acetyl-L-carnitine, which is involved in mitochondrial lipid metabolism and maintaining efficient mitochondrial
Lipoic acid is an antioxidant nutrient capable of redox recycling of other antioxidants and raising intracellular glutathione
levels. Glutathione is the major intracellular water-soluble antioxidant.
In one example from the study, dogs were fed the control or enriched food for six months and tested on four oddity discrimination
learning tasks that became increasingly difficult. Aged dogs made significantly more errors than young dogs in all tasks.
This would seem to support the adage that "you can't teach old dogs new tricks."
However, old dogs receiving the enriched food performed better on all tasks than old dogs eating the control food. The enriched
food produced the most significant improvement in the ability of old dogs to learn complex tasks.
Another component of this study was to determine the effect of environmental enrichment on learning ability in old dogs.
Half of the control diet dogs and half of the enriched diet dogs were given an enriched lifestyle with an increase in daily
walks, new toys and a regular cognitive testing.
At the end of two years, the dogs with the combination of enriched environment and enriched food scored statistically better
in the learning tasks than those dogs given an enriched environment or enriched food alone.
- Reduction in age-related behavior changes?
In addition to the extensive laboratory testing reported above, a randomized, double-blind, controlled clinical trial was
conducted to evaluate effects of dietary enrichment in dogs with age-related behavioral changes.