Thinking about Stress and Disease in Turkeys

What is stress? You have probably been told time after time that reducing bird stress will help to fight E. coli infections. But just what does that mean? Perhaps if you think about what stress means to you, it may help you to understand what you can do to decrease the stressors faced by your birds.

The word 'stress' means different things to different people. "Stress" was originally an engineering term meaning a force that strains or deforms. 'Stress' was first used in a biological sense by a Harvard physiologist, Walter B. Cannon in 1914. Cannon used the term to describe the effects that emotions have on physiology and health. However, the term "stress" became popular in a biologic sense beginning with the work of Hans Selye. In 1950, Selye published an influential book summarizing his work studying "The General Adaptation Syndrome" and the diseases of adaptation titled The Physiology and Pathology of Exposure to Stress. Since then, this concept has become so common, that today the biologic sense of the word is probably the first that comes to most peoples' minds.

Awareness of stress and the effects of stress has become so pervasive in our modern society that in June of 1983, Time magazine ran a cover story which referred to stress as "The Epidemic of the 80s." Awareness of the effects of stress has escalated since then. A brief search on the internet brought up the following varied definitions submitted by individuals:

 

As William Shakespeare once said "NOTHING IS GOOD OR BAD BUT THINKING MAKES IT SO", which is one reason the effects of stressful situations are so different for different individuals. In today's world our stressors include but are certainly not limited to:

Traffic jams, deadlines, eating on the run, an angry spouse, or boss, or parent, teenagers, bills to pay, a job, no job, new job, job changes, moving, living on unemployment, endless chores, screaming kids, school, tests, pop quizzes, getting called on in class, talking in front of an audience, writing assignments, bereavement, divorce, poverty, friends, no friends, errands and demands, demands, and more demands. And today we know the fear of war, fear of terror, fear of the unknown.

Stress would seem to be a scientifically unworkable concept. However, we know that stress has adverse effects, even without ever having resolved the problem of precisely defining stress or even agreeing on ways to measure this condition. The best we can try to do is measure 'stress' by concentrating on the effects stressors have in our lives. Transferring this thinking to our animals, we need to pay attention to the effects of stress on reproduction, immunity, and metabolism, all of which serve as indicators of animal well-being.

It has been documented that stress can lead to an increased susceptibility to disease. The confusing part is that stress can also lead to an increased protection from disease. The effects of stress are so variable because: 1) The effects are specific for the type, degree, and duration of stress; 2) Effects are influenced by the complexity of the immune system and the neuro-endocrine system; 3) Effects are strongly influenced by individual genetic differences in physiology as well as the psychological response or perception of different stressors; and 4) The development of each individual response to stress is strongly influenced by the environment, which includes all previous experience, as well as nutrition and disease.

Our research program uses an experimental disease model to produce E. coli air sacculitis and osteomyelitis in turkeys by "stressing" birds with injections of one of the major chemicals involved in the birds' response to stress. A general response of birds to stress is the release of ACTH from the anterior pituitary gland which stimulates the adrenal cortex to increase the synthesis and secretion of corticosterone, the major glucocorticoid in birds. Dexamethasone, the chemical we inject, is a synthetic glucocorticoid that is commonly administered to cattle for the treatment of many problems including mastitis, ketosis, udder edema, respiratory disease, inflammatory musculoskeletal disease, and induction of parturition. However, dexamethasone usage is a good example of a treatment that can become worse than the problem when used in excess. Just remember that a little stress is good for you, but too much is a killer. Dexamethasone decreases immunity to coccidiosis in chickens and in our studies, dexamethasone treatment leads to E. coli and S. aureus air sac infection and osteomyelitis. This model clearly and reproducibly shows that too much stress can lead to an increase in disease in turkeys and that by reducing the effects of stress you can dramatically increase the health of your birds.

But, what can you do about it ??? If the effects of stress are so complex, why even bother trying? Probably the easiest and most important thing you can do is to just think. Think about how your birds can be stressed, and then do all that you can to fix the situation. A lot of things just can't be changed, but many can be improved by a little consideration. I've had fun trying to list the stressors I know can be faced by poults throughout a growout and I've listed them below.

My challenge to you is to try to think of more. What is it in your particular situation that can produce unexpected changes in the environment, unexpected surprises for your birds. What are they afraid of? A turkey grower in Kansas, after reading this list, realized that running the housekeeping tiller in his brooding house was really scaring his poults. He believes that since he stopped tilling, his birds have had less osteomyelitis. Coincidence? Maybe. But if you add together all of the little things you can do to make birds more comfortable and less fearful, you will make a big difference in bird health. For turkey growers, one of the greatest stressors on the poults is having to move their birds from one house to another in a multi-stage system. We need to find alternatives to these types of management practices that really impact health and disease. We are searching for ways to improve the birds' stress response through genetics and nutrition. But until real solutions are found, decreasing stress is up to you. Think about ways to decrease the fear and reduce the changes faced by your birds.

Since September 11, all Americans have experienced a new kind of stressful anxiety caused by not knowing what will happen next, a feeling of loss of control and an inability to plan our next response. Perhaps this general uncertainty, even though it is so hard to describe, so hard to even know when we are feeling it, may be our best connection to understanding the stress experienced by our poultry flocks. As humans we have developed an intuitive feeling for the concept of stress from our personal experiences. For your birds, the term stress can be used to describe everything from the discomfort caused by high or low environmental temperatures, or running out of feed, to the anguish of emotional or physical conflict with no place to hide. Perhaps the best thing you can do to reduce stress in your flocks is to try to maintain a sense of consistency as best as possible. Make careful observations and be aware of ways you can reduce fear and uncertainty. And continue to think about how sometimes big changes and sometimes small changes in our lives and our environment can profoundly affect the way we feel.