Understanding stress and shock

Just as with injured humans, shock is often the number one cause of death in injured wild animals. As the first person to encounter the injured animal, you are in the best position to minimize that animal's shock and stress.

Shock is essentially the loss of heat and fluids from the body--a natural response to injury. Interaction with a human causes additional stress to an injured wild animal and this can kill an already shocked animal. So keep in mind that fear, noise, and cold temperatures all contribute to the animal's stress. You can reduce this stress significantly by following CWC's advice about how to best house and transport the injured animal.

Perhaps it is natural for us to want to hold, pet, and comfort an injured wild animal, but the animal does not understand our good intentions. To a wild animal, we are just another potential predator. Holding them or touching them is extremely stressful, as studies and our experience have shown. The only cases we've seen where animals haven't appeared afraid of us were raccoons with advanced canine distemper, very young baby birds, and semi-conscious animals with concussions.

What is stress and what effect does it have on the animal physically?

by Becky Picton

Stress usually involves situations of stimuli that we consider threatening, frustrating, or out of our control. The same is true for animals. When most wild animals become threatened or frightened, they respond by "flight or fright."

During the "flight or fright" response, a complex series of changes occurs in the body. Basically, the amygdala (part of the brain) signals the hypothalmus (also part of the brain), which then mediates an all out stimulation of the sympathetic portion of the autonomic nervous system. Where these nerves contact organs of the body, they release either epinephrine or norepinephrine (neurotransmitter compounds), thus stimulating the organs to prepare for vigorous activity.

The medullary portion of the adrenal gland is also stimulated to release these two compounds into the blood circulation for a prolonged stimulatory effect on these organs. Changes that occur include an increase in heart rate and force of contraction, increase in arterial pressure, release of glucose from the liver, dilated bronchi, decrease in gut activity, and dilated pupils.

Constant or long-term activation of this response appears to be linked to hypertension (mainly due to permanent damage to the kidneys), arteriosclerosis, and other cardiovascular problems.

When a fight or flight response doesn't work, and the animal becomes very frustrated or distressed, it may adopt the conservation-withdrawal response. This response is initiated by the hippocamus (part of the brain), which signals the hypothalmus, which in turn releases components that stimulate the pituitary gland. The pituitary produces a compound, which in turn activates the adrenal cortex to release corticosteroids. Those in turn have various side effects, such as suppression of inflammation, and changes in metabolism of carbohydrates, proteins and fats

The resulting benefits in cases of stress are not totally clear, but are probably the increased availability of glucose, amino acids, and fatty acids, and the more efficient use of glucose by the cells. An animal in conservation-withdrawal will appear quiet and depressed. People misinterpret this behavior to mean the animal "understands we are trying to help it."

Other physiological events that occur (mediated mainly by the vagus nerve) are a decrease in heart rate, sometimes to the point of stopping completely, pooling or sludging of blood in the vessels, and loss of appetite. The animal may die "for no apparent reason."

Long-term corticosteroid release suppresses the immune system, and allows for disease to occur more easily. The effect of stress on the immune system and subsequent increase in disease susceptibility are current topics of much research. The mind-body connection is poorly understood, but undeniable.

Corticorsteriods also stimulate acid release in the stomach (as does nerve stimulation via the vagus nerve), which can lead to peptic ulcers. Both the fight or flight response and conservation-withdrawal cost the animal physically. Both disrupt normal metabolism, growth, reproduction, and immune function, and can also caused an animal to self-mutilate, something we have seen at the Center a number of times.

Stress can be a cumulative process. Each stressor by itself may not be significant, but when they affect the animal sequentially or simultaneously, they may push it over the threshold toward illness or death.

What are some of these stressors? Handling by humans, strange sights, noises and smells, unfamiliar foods or lack of food and water, restraint, injuries, heat, cold, light, and the presence of people's pets.