Energy is needed to make these adjustments. Whether the adjustment is either great or small, physiological stress provides the energy to accomplish the adjustment through nonspecific responses. For every external demand, or 'stressor' (a situation that causes stress), there is both a specific response and a nonspecific response. The specific re- sponse is unique for each stressor but the nonspecific response is essentially the same for every stressor. Since the presence of stressors is constant, by definition the absence
of stress would be death. We cannot totally avoid stress, we must manage it.
The concept of physiological stress was first developed by a scientist named *Selye (1936,1973), who termed his observations General Adaptation Syndrome (GAS). Selye observed that most chronically ill individuals exhibited similar symptoms. There are three stages in the 'General Adaptation Syndrome'. The first is the alarm reaction or the
so-called 'fight or flight' reaction.
At this stage a sudden biochemical reaction takes place, (characterized by huge releas- es of adrenaline and similar hormones from the sympathetic nervous system). These compounds cause rapid release of glucose from body reserves (primarily from glyco- gen). This produces available energy to elude a stressor. The animal quickly enters the stage of resistance. This is the period when glucose is formed from less available re-
serves such as lipids and proteins.
The important aspect of the stage of resistance is that it will continue until recovery from the stressor occurs or the animal enters the stage of fatigue and dies. The animal dies from either the depletion of reserves or adrenocortical exhaustion. That is when the adrenal cortex (the source of corticosteroids) depletes the survival functions which in- clude regulation of heat loss, blood flow and respiration etc. so that they can no longer be supported. The time course of the three stages of the 'General Adaptation Syndrome' depends upon the severity of the stressor. A chronic stressor requires small changes
over a long period of time.
The adaptation to warmer weather that takes place over several weeks during the start of summer is an example. An acute stressor requires immediate life-saving adaptations to survive. The sudden onset of very hot weather creates such a situation. The animal has not had sufficient time to adapt to the hot weather. In the latter case an alarm reac- tion is followed by a resistance stage. If the adreal-cortex is depleted before the stressor
is removed, then death will occur.
Although they may seem unlikely, growth and reproduction both call upon the body to constantly change, and are by definition stressors. With a seemingly endless myriad of stressors, the challenge for modern animal management is to modify or manage physio- logical stress. Ascorbic acid (vitamin C) supplementation has been shown to reduce heat stress related mortality in birds (*Pardue, 1983). One of the most difficult
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85