Study Finds High Protein Diet Improves Birds' Ability to Tolerate Infection

Russell Cothren, University Relations

Erin Sauer

Whether you feed bread to ducks at the local pond or hang a bird feeder on your back porch, the food you’re offering wild birds plays a role in their ability to tolerate infection. New research from the U of A found that canaries fed a high protein diet fared better when it came to immune function and tolerating infection than canaries fed a high lipid, or fatty, diet.

The findings included molecular analysis of blood draws, revealing how different diets trigger the expression of different, immune-related genes, both before and after infection.

“Our results are exciting because of the importance of human supplemented food in wildlife disease systems, especially wild birds, which are commonly provided with supplemental food via bird feeders,” said Erin Sauer, a first co-author on the study.

Published in Molecular Ecology, the paper’s six authors are or were affiliated with the U of A at the time work was conducted. In addition to Sauer, a postdoctoral fellow in biological sciences who has accepted a faculty position at Rutgers University, the other first co-author was Carson Stacy, a Ph.D. candidate in biological sciences.

Outline of the Study

Carson Stacy, doctoral candidate in biological sciences. (Photo by Whit Pruitt, University Relations)

Birds were offered food bars that contained either more egg whites or more egg yolks and oil, increasing the amount of protein or lipids, respectively, in their diet. The science of bioinformatic analysis is complicated, but essentially data analysis indicated birds eating a high protein diet were more transcriptionally “ready” to combat infection — in that more immune-related genes were highly expressed (or upregulated) in birds eating a high protein diet than in birds eating a high lipid diet.

Following exposure to a common avian bacterial pathogen, the birds were tested again. Birds fed the high lipid diet saw increased (or upregulated) expression of immune-related genes after infection, while the birds fed a protein diet showed a less pronounced response because their immune systems had already been primed to fight infection. Birds fed high-protein diets also showed more tolerance for the pathogen, as measured by the degree of eye inflammation, a common symptom.

In short, their protein-heavy diet resulted in a molecular signature with higher levels of gene expression for immune defense genes, as well as reduced symptoms and increased resistance to the disease.

“To our knowledge, this is the first study to examine the molecular mechanisms underpinning diet-driven infection tolerance in any wildlife system,” Sauer said. “Our study provides important insight into the ecological and immunological consequences of human behavior on wildlife disease.”

Food for Bird Feeders

What are the implications of this study for those filling bird feeders? Sauer suggests buying bird food that is nutritionally dense in both protein and fat. This can include things like suet blocks with seeds, mealworms and fruit mixed in or food that contains sunflower seeds or peanuts. Foods to avoid are composed mostly of cracked corn, millet or bread, which are not as nutritious.

She also noted that there’s no need to overcorrect by only providing high protein food. There are times when birds may need a little more fat in their diet, and they will prioritize what they eat accordingly.

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