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Common causes of chicken stress

A chicken utilises various behavioural and metabolic mechanisms to maintain a homeostatic internal environment and ensure normal physiological function. A deviation from this homeostatic condition is called “stress”. Commercially farmed chickens are subjected to conditions that constantly challenge their ability to maintain this homeostatic state and chicken stress has a significant effect on the overall health and productivity of a flock. It is therefore important to understand the factors that contribute to stress. Identifying and managing these factors is a critical part of successful poultry production.

 

Temperature stress – Heat and cold

Chickens have a body temperature of 41°C and aim to maintain their body temperature within a thermo-neutral zone (TNZ). Chickens in a commercial environment have limited mechanisms for temperature control and are therefore susceptible to extreme cold or heat, or a dramatic change from one to the other.

 

Heat stress occurs during hot conditions when birds experience difficulties in achieving a balance between body heat production and body heat loss and the body temperatures tend to move outside of the TNZ. Maintaining a body temperature with the TNZ requires behavioural changes, including panting, that demands energy and alters blood pH. Another response is to minimise body heat production by reducing feed intake and consequently the heat increment of digestion. Both these responses have negative effects on production.

 

Environmental stress – Air, light and litter

A commercial chicken’s environment typically refers to its housing. Housing, or environmental, conditions include factors such as air, light and litter (bedding) quality. Poor ventilation can lead to poor quality air (high levels of CO2 and ammonia) and heat build-up which will stress the bird. Chickens in deep-litter systems are in constant contact with their bedding and the condition of the litter will affect the bird’s comfort and wellbeing. Litter condition is a product of feed, water and ventilation management, as well as stocking density and bedding material selection (and its absorbency). Artificial lighting (duration) and light intensity are “foreign” to chickens and can place the bird under undue stress if not managed correctly.

 

Physiological stress – Production and reproduction

The activities surrounding breeding and laying an egg are stressful, especially with the first season of maturity for either sex. Laying of the first egg for a hen can be difficult, both in the hormone changes that occur and in the physical exertion it requires. Most mortalities due to diseases such as Mareks occur right before or right after sexual maturity due to the stress that these activities place on the bird.

 

Pathological stress – Disease

Exposure to infectious agents is a common cause of stress. When sub-clinical infections due to poor bio-security and sanitation persist then excessive activation of the chicken’s immune system will result in a condition known as immunological stress. This condition results in a series of changes in the nutrient metabolism induced by mediators of the immune response and production will suffer.

 

Social stress – Housing

Chickens are social animals and they will establish a hierarchy, or pecking order, within a flock. Moving or swopping birds will disrupt this hierarchy leading to stress and a consequent drop in production. Overcrowding of chickens due to the incorrect stocking densities being adopted or improper house (equipment) lay-out will also result in stress.

 

Physical stress – Handling

Chickens are a prey species so naturally if caught and picked up they become stressed. Harsh handling of chickens during vaccination, weighing, transfer, harvest and transportation will all contribute towards stressing the bird.

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