GAS, that weakens the general immunity in chickens
There is a strong link between the stress and immune response of the birds. This article takes the learnings from the breakthrough work of research done by Selye in 1936 and Faber in 1964. Selye is the first scientist to give a scientific explanation for biological stress through General Adaptation Syndrome (GAS) model. Faber has reviewed more than 100 research articles to check the relevance of GAS model in Poultry science.
Some key points discussed in this article are
• Animal adapted to one stressor loses much of its resistance to other stressors (cross sensitisation)
• Milder stressors affect the adrenals and the lymphatic system
• The link between stress and immune status of the birds
• Ascorbic acid levels deplete in matured (laying) birds during the stressful condition
• Anti-stress feed additives are necessary to manage the stress and immunity
Hans Selye (1907-1982) was a Hungarian endocrinologist. Selye is the first scientist to give a scientific explanation for biological stressin the year 1936. Selye explained his stress model as General Adaptation Syndrome (GAS). His model states that an event that threatens an organism's well-being (a stressor) leads to a three-stage bodily response:
Figure 1: General Adaptation Syndrome (GAS) model (Selye, 1950) & adaptogens (Pannosian & Wikman, 2010)
GAS applied in Poultry
Selye's theory greatly influenced the scientific study of stress. GAS model was intensely reviewed later by Hans von Faber in World's Poultry Science Journal. Faber reviewed 109 articles to write his paper which made the GAS model relevant to Poultry science. Many of the following stressors are listed by Faber in his article. These stressors are still relevant and present at most of the commercial poultry farms.
| • Heat
|| • High metabolic
|| • Debeaking|
| • Cold
|| • Handling|
| • Vaccination
|| • Toxins in the feed
|| • Restraint (caged birds)|
| • Crowding
|| • Limitation of feed &
|| • Moulting|
| • Noise
| • Infections
|| • Wetness
Faber states, an animal adapted to one systemic stressor loses much of its resistance to other systemic stressors (cross sensitisation). Meaning, if the birds are adapted to one stressor (such as crowding, restraint or production stress) then it’s challenging for them to resist other stressors whenever they occur. The birds undergo the 3 stages of GAS model in presence of any stressor.
Table 2: Stages in General Adaptation Syndrome (GAS) model (Selye, 1950)
1. Alarm Stage
2. Resistance Stage
3. Exhaustion Stage
• Upon encountering a
stressor, body reacts with
• Body returns many
physiological functions to
• Stressor continues
beyond body's capacity
• Hormones (such as
corticosterone) released into
• Body focuses resources
against the stressor
• Body exhausts
resources and becomes
susceptible to disease
• The body's resources now
• Blood glucose levels remain
(corticosterone) continue to
circulate at elevated levels
Effect of GAS on the immunity
According to Faber, the most prominent morphological and functional changes in the birds during GAS are:
1. Enlargement of adrenals together with an increased output of corticosterone.
2. Increased level of corticosterone reduces the proteins (antibodies, enzymes, muscles) which affect the immunity,
digestibility, growth and production.
3. Reduction in the size of thymus, spleen and bursa compromises the proliferation of the lymphocytes which are
very important for the specific and general immune response.
4. Changes in the circulating leucocytes i.e. a decrease of lymphocytes and increase of heterophils.
5. Ascorbic acid levels deplete in matured (laying) birds during the stressful condition.
Saving the chickens from GAS
Faber suggests the supplementation of anti-stress additives in the diet because, an animal adapted to one systemic stressor loses much of its resistance to other systemic stressors (cross sensitisation). Therefore, an anti-stress diet may not only help to overcome the existing stress but may also increase the resistance to other stressors, as for example, infections.
PHYTOCEE® is an Adaptogenic, anti-stress and immunomodulatory feed additive by Natural Remedies Pvt. Ltd. The effect of PHYTOCEE® is proven through number of scientific studies conducted on various parameter related to the stress and immunity in the birds. The scientific studies done with PHYTOCEE® are covering the relevant haematological, immunological, serological and endocrine parameters as listed below.
PHYTOCEE® an anti-stress feed additive
a. Protects the animals from production stress by acting as an anti-oxidant (Joseph et al., 2015; Chandrasekaran et al., 2009)
b. Thermoregulatory effect of PHYTOCEE® helps in maintaining the body temperature during climatic variation (Selvam et al.,
c. PHYTOCEE® controls the corticosterone levels to prevent ill effects of stress in animals (Selvam et al., 2016)
Figure 2: PHYTOCEE® controls the level of corticosterone (Selvam et al., 2016)
PHYTOCEE® as an immunomodulator
a. Improves the pre-immunization H/L (Heterophil/Lymphocyte) ratio (Selvam et al., 2016; Rama R.)
b. Improves the proliferation of lymphocytes (Rama R.)
c. Lysozyme activity for inhibition of pathogenic bacteria in serum was enhanced by PHYTOCEE® (Manukian et al., 2013)
d. Enhances the phagocytic activity of macrophages (Anonymous)
e. PHYTOCEE® optimizes the vaccine titres in treated birds (Rama R.)
PHYTOCEE® also maintains the normal level of ascorbic acid in the blood of the birds after 100% replacement of synthetic Vitamin C from the feed (Manukian et al., 2013).
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Article made possible through the contribution of Dr. Vinayak J. Surve and Natural Remedies Pvt. Ltd.