Stress in Poultry

Stress is defined as a non-specific response of the body to any demand from the environment. Stress can alter the steady state of the body and challenge physiological adaptive processes. Nutrition and stress are closely linked and are interactive. A stress can produce or aggravate nutritional deficiencies. Similarly nutritional deficiencies can produce a stress response. Major stress factors include feed and water depravation, temperature (heat and cold) and disease, as well as social and psychological factors.

Stress Factors Management of Stress   See Also: Heat Stress Management Related Problems Diseases in Poultry References and Further Reading

An understanding of the relationship between animal production characteristics and stress are also important considerations in issues of animal welfare.

A wide range of environmental, social and management related factors can be responsible for stress in poultry. Factors responsible for causing stress can be found in any poultry rearing facility, and range from temperatures that may be too hot or cold, an environment that is too wet or dry, to poor quality feed, water or air, as well as the presence of infectious agents.

Intensively reared chickens have been selected to have a genetic potential for rapid growth and efficient feed utilization. However, this genetic potential is also prone to undesirable stimuli or stress factors. The resulting stress reduces the ability of the birds to express their full genetic capability. In contrast, lower performance, traditional, backyard or village poultry are less likely to be affected in the same way by stress factors.

Rapid growth and high egg production are themselves a source of stress. Additional stress is likely to result in a reduced growth rate or in the production of fewer eggs, as a way of coping with the stress, and therefore efforts should be made to reduce to a minimum all other potential sources of stress.

The publication by Downing and Bryden (2002) includes a comprehensive literature review of stress in poultry and should be consulted for in-depth information.

Stressors can be grouped as follows:

• Climate (heat and cold)
• Environment (light and dark)
• Nutritional
• Physiological
• Disease
• Social
• Psychological (fear)

Poor management is a common stress related problem, and can result from factors such as incorrect temperature, poor air quality, and the presence of disease. Such management related stresses should be relatively easy to identify and correct.

A common stress response is an alarm reaction. This involves the nervous system and increased output of adrenaline, and in turn triggers various secondary physiological changes such as an increased heart rate, and shunting of blood from the skin and viscera to the skeletal muscles, i.e. the classic "fight or flight" response. The results are elevated heart rate, increased plasma corticosterone and catecholamine levels, adrenal hypertrophy and atrophy, immunosuppression, changes in growth and reproductive hormones and neurochemical changes .

Common forms of stress in commercial poultry systems include:

	Heat stress (any extremities in temperature, both hot and cold).
	Overcrowding, perhaps due to poorly designed housing or otherwise inadequate facilities. Fighting for space at a feeder or drinker will result in injury, and in reduced growth or productivity. Overcrowding increases the exposure of disease causing organisms and often increases the opportunity for the growth and spread of these organisms.
	Moving, e.g. from a hatchery to farm or from one building to another.
	Vaccination. Negative reactions from some vaccines may occur up to 10 days after inoculation.
	Temporary, as well as longer term, shortages in feed or water.
	Changes in feeds or feeding methods, or changes to a daily routine.
	Poor nutrition. Inadequate diets may result in deficiency diseases and general lowering of resistance to infection.
	Parasites (both external and internal). They weaken the bird and provide additional opportunities for the introduction of other disease causing organisms.
	Physical disturbances such as excessive noise or other unnecessary activity. These may for example result in fear. The fear response can range from mild avoidance to extreme hysteria.
	Low social ranking. Birds that are lower in the "pecking order" are more likely to suffer from stress.
	Frustration. This can be mild but if prolonged can lead to increased aggression and to stereotypic behaviour.

Production systems should provide chickens with:

	Freedom from hunger and thirst	This requires ready access to fresh water and a diet to maintain full health and vigour.
	Freedom from thermal and physical discomfort	By providing an appropriate environment including shelter and a comfortable resting area.
	Freedom from pain and disease	By taking preventive measures, and by taking prompt action when disease is suspected.
	Freedom from fear and distress	By ensuring physical conditions and standards of care which avoid mental suffering.
	Sufficient space to exercise, or freedom to express normal behaviour	By providing sufficient space and proper facilities to enable social interactions, as well as normal body functions such as preening and dust-bathing. Space to avoid interactions may also be important for those individuals that are lower on the pecking order.

The last of these five freedoms, i.e. the provision of sufficient space, is currently a controversial tropic, and one that is increasingly governed by legislation. Intensive farming practices have reduced the available space to a minimum and in doing so deprive an animal's access to conditions that allow it to exhibit a normal behaviour. It has been considered that this deprivation leads to increased levels of stress and to a decline in the animals well being (see Downing and Bryden, 2002). Similarly, the increased levels of stress are more likely to lead to disease outbreaks, and when combined with the high density of birds involved, such outbreaks can be severe.