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Immune function plays an important role in a dog’s health and well-being. A key ingredient of healthy immune function is good nutrition, or simply put, what a dog eats.
“What a dog eats impacts overall health,” says Ebenezer Satyaraj, Ph.D., Purina Senior Research Scientist. “Because the immune system and metabolic system, being essential for survival, co-developed during evolution, a dog’s diet has a significant impact on his immune health, both positive and negative.”
Immunonutrition is an emerging field that evaluates the impact of diet on immune function, particularly the diet of an individual dog in relation to his or her health condition. In the past, researchers focused on understanding the effect of malnutrition on immune health. Today, the focus is on how immune function and nutrition relate to life stage and stress in healthy dogs.
“Most dogs in this country are not malnourished,” Satyaraj says. “Rather, they suffer from other conditions — things like overnutrition or undernutrition — that can impact immune function. Even life stage and stress have a barometric effect on immune function.”
In humans, T lymphocytes, which are part of the immune system, recognize pathogens in the body and secrete proteins, called cytokines, that are responsible for the body’s response to stress, infection or inflammation. There are two main subsets of T lymphocytes: Th1 lymphocytes secrete cytokines, which produce inflammation to help deal with pathogens such as bacteria and certain viruses; and Th2 lymphocytes secrete cytokines, which tend to be anti-inflammatory.
Just as in humans, a dog’s life stage helps determine how well he responds to stress and illness. Newborn puppies, for example, have a Th2 bias. “This means puppies cannot ward off infection from outside pathogens immediately as they would if they had a stronger Th1 response,” says Satyaraj. “Young animals have inefficient antigen-presenting cells (APCs) to fight illness.
Similarly, senior dogs have a lower immune response due to age-related decline, principally thymic atrophy, which affects the production of T lymphocytes, and hematopoietic bone marrow defect, which causes abnormal production of blood cells. “Senior dogs also have increased oxidative stress, low-grade inflammation and inefficient APCs,” Satyaraj says.
The impact of stress on canine immune function continues even after the stressor has ended, at least based on research in humans. “People who were the primary caregiver for a spouse with severe Alzheimer’s disease experienced lower vaccine responses even after the stress of caring for the spouse was no longer present in their lives,” says Satyaraj. “We believe dogs have a similar response.
“The reasons for this include inefficient APCs and the presence of stress hormones, such as glucocorticosteroids, epinephrine, norepinephrine and catecholamines, which dampen immune response. We believe this occurs in dogs when they experience stress due to travel, hard work or poor nutrition.”
Recapping, Satyaraj says, “young dogs experience hormonal and cell maturation deficiencies, old dogs experience tissue atrophy, and stressed dogs experience hormonal imbalance. All have APC inefficiencies.”
Immunonutrition can help modulate immune health in all three age-related examples. “Three things impact a dog’s immune system: genetics, life stage and lifestyle, which includes diet. Though a breeder or owner can’t impact the first two, he or she can influence what a dog eats,” Satyaraj says.
Immune cells are clustered and dispersed along the mucosal tissue in the gut, Satayaraj explains. “These cells monitor what goes through the gut and what drains into the lymphatic system. About 65 percent of the body’s immune cells are in the gut, organized as GALT (gut-associated lymphoid tissue).”
Feeding a dog food that offers complete and balanced diet is one way owners can aid healthy immune function. Another way is maintaining dogs in optimal body condition and avoiding obesity. This helps to promote increased life span and decreased onset of age-related decline.
Cutting-edge nutritional research is looking at ways to target innate immune receptors in the gut with specific immunomodulatory ingredents that could be added to dog food. “This would help overcome the Th2 bias seen in puppies as well as senior dogs,” says Satyaraj.
“One Purina study examined the effects of bovine colostrum on 24 Alaskan sled dogs, ages 2 to 6 years,” he says. “The dogs were fed a control diet or a control diet plus bovine colostrum. Immune and gut health was monitored over the 40-week trial via fecal IgA (immunoglobulin A) and gut microflora measurements and evaluation of systemic immune response to canine distemper virus vaccine. The colostrum group showed clear immune status enhancement.”
Another novel approach being studied is personalized immunonutrition. “By influencing the immune system to have a specific outcome, we will see healthy outcomes,” Satyaraj says. “In dogs with IBD (inflammatory bowel disease), for example, we may be able to produce good results by reducing inflammation.”
Personalized immunonutrition via targeted dietary strategies is likely to become more readily available for clinical management of diseases such as IBD. Taking a strategic approach to canine nutrition — since nutrition interacts with the immune system at multiple levels — can lead to more focused modulation of the immune system in healthy dogs at all life states and lifestyles.
Used with permission from Today’s Breeder magazine, Nestlé Purina PetCare.
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