Impacts of stress on broilers

By MARTIN LOBAO
PROBLEMS associated with broiler production is related to or caused by a combination of factors such as management, nutrition, immuno-suppression and exposure to disease agents and stresses.
Stress is an important cause of reduced performance and increase susceptibility to diseases.
Broilers under intensive production systems are frequently exposed to stress factors, reducing their ability to perform effectively to their potential. It is, therefore, important to have an effective management programme to minimise their effect on the birds’ performance and health.
Stress response studies require an integrated know-how of the animal’s response to both external and internal factors. Thus, an attempt to give detailed information on these integrated mechanisms for all types of animals is beyond the scope of this article.
I will only focus on how stress affects both product quality and production of broiler chickens. This article will briefly define the term “stress”, the common sources of stress and explain some impacts of stress.
Stress was originally described as a “fight or flight syndrome”.
It is any physical or mental disruption that lowers resistance and the ability of an animal to perform up to its expected potential.
It is also defined as a set of responses to external demands, which enable flocks to adapt to new or abnormal situations. This adaptation process causes the release of hormones and requires the redistribution of body reserves, including energy and protein, at the cost of decreased growth, reproduction and health.
After extended or repeated periods of stress, birds become weak; they often succumb to starvation and infectious diseases.
Stress can be described as detrimental effects of a variety of situations on the health and performance of poultry.
The most common sources of stress include climatic stress (extreme heat and cold, and high humidity); environmental stress (bright light, wet litter and poor ventilation); nutritional stress (shortages of nutrients, feed intake problems); physiological stress (rapid growth and process of maturing sexually); physical stress (catching, immobilisation, injections, transport); social stress (overcrowding, poor body); and the psychological stress (fear, harsh care and weight uniformity). These can be simply be classified into mental, physical and or a mixture of both. Other classification of stress includes psychological and physical stress. These classifications summarise most of the factors associated with stress on any poultry production system.
Some of the most common causes of stress in broilers production include poor brooding and litter conditions, contaminated premises, temperature extremes, inadequate ventilation, and handling and transportation.
Mental stresses in broiler chickens are a very complicated process. Since broilers live a relatively short life (5-8 weeks) and for them to perform up to their genetic potential whilst coping with different stress factors is certainly a very challenging process. Sudden disruptions of their life-style are likely to be bewildering to the birds, as they have neither the time nor the experience to react to such disturbances.
Like other non-aggressive animals, broilers are very fearful.
Fear is an important mental stress that causes negative effect on the welfare of the birds.
Broilers are continuously exposed to mental stress especially during social group disruption, time of catching, crating and when transporting.
Physical stresses are factors that cause physical injuries.
Broiler chickens often exhibit signs of physical stress during time of harvesting and transportation, which mainly involve catching of birds by the legs, handling of birds, loading of birds and crates, transportation, unloading of birds and so on. Other injuries sometimes occur when the feeders and drinkers are removed during feeding times.
Environment is a composite of interacting stressors that can include, in a broadest sense, all the conditions in which the birds live. These include external stressors such as temperature, light, social and behavioural environments; and the internal stressors such as pathogens, toxins and metabolic disorders.
Transporting and handling of the birds pose a mixed factor of mental and physical stresses.
Birds experiencing stress undergo a variety of internal metabolic and hormonal responses.
During the growing period, stressed birds do not gain weight and have reduced feed efficiency (ability to convert feed into meat).
Extreme heat or cold can affect the performance of broilers by reducing body weight gain, in addition to increasing mortality and susceptibility to disease. The influence of this type of stress during the brooding period can have devastating effects on the immunity and future performance of the broilers.
Quality of poultry meat is an important aspect in any commercial broiler enterprise.
Quality meat is largely determined by a low microbial contamination and the acidification process of the meat post-mortem.
Broilers under intensive production systems constantly expose to frequent stress factors. 
This includes climatic stress, environmental stress, nutritional stress, physiological stress, physical stress, social stress and psychological stress.
No matter how much resistance a bird has, its resistance will be reduced to some extent by stressors.
It is important as well as crucial under animal welfare guidelines for industries and farmers to have in place effective management programme to minimise their stressors effects on birds’ performance and health. Stress cannot be avoided and is a part of every bird’s life.
Farmers can minimise these stresses through good management on the sources of these impacts on production.
Any management tool that minimises stress will result in improved productivity as well as improved efficiency of feed conversion in broiler.