What are the common causes of stress responses in chickens?

In @#@230@#@ production, especially under intensive production conditions, the chicken body has a certain capacity to respond and adapt to stimuli from factors such as stocking density, climate, vaccination, transfer between houses, group splitting, catching, beak trimming and lighting. If the intensity of these stimuli is too great or their duration too long, exceeding the body's physiological tolerance, then the chicken's growth, development, reproduction and disease resistance are affected, and death may even be caused directly. The factors that cause chicken stress mainly include the following aspects.

1. Physiological stress. High-yielding chickens raised on a large scale are all kept in cages or in houses. If the absolute amount of feed is insufficient or the nutrients are unbalanced, adrenal cortex hormone deficiency occurs, causing stress. When chicks are in a state of stress, they require large amounts of vitamins, more than 1 times their normal requirement.

During non-stress periods, in order for broilers to utilise feed reasonably, they need abundant vitamin C. Normal chickens can synthesise part of their vitamin C, but during stress periods, because the synthesising capacity is reduced, the stored amount of vitamin C in the adrenal glands is easily lowered.

2. Environmental stress. The living environment of chickens includes temperature, light, gases, noise and so on.

1. Temperature: Under normal circumstances, when the air temperature is within the range of 18-23°C and the relative humidity is within 60-70%, the growth rate and egg production of chickens can reach their best levels. If meteorological conditions change sharply, such as temperatures above 30°C in summer, temperatures below 5°C in winter, or a daily temperature difference of more than 10°C, then the growth and development of broilers will be affected. When the environmental temperature reaches above 30°C, besides the stress response, there are also heat stress responses such as reduced sperm production in roosters, delayed sexual maturity in hens, a marked drop in fertilisation rate, lowered blood calcium content, disturbed blood acid-base balance, and in severe cases a very high mortality rate. Cold also makes chickens huddle together, and weak chicks are often crushed and injured or crushed to death.

2. Light: Unreasonable lighting, or a sudden change in light duration and light intensity, can cause strong stress in chickens, especially laying hens, resulting in a significant drop in egg production.

3. Gases: When chicken density is high, ventilation is poor, and chicken manure accumulates and becomes damp, large amounts of ammonia gas are easily produced. When chickens live long-term in an environment with a high ammonia concentration, it not only slows the growth rate of broilers and reduces the egg production of laying hens, but also damages the cardiovascular system and causes infection of respiratory diseases and the occurrence of ascites.

4. Noise: If sound exceeds the standard of 45 decibels set by the World Health Organization, or there are abnormal sounds, sudden sounds and other noises that occur repeatedly, chickens are all very sensitive to them. For example, the noise produced by firecrackers, airplanes, cars, trains and so on can all cause stress responses in chickens, leading to reduced appetite and decreased egg production, and even death.

3. Management stress. Stress caused by mistakes in feeding management is the most common stress in chicken production and also the one with the greatest impact.

1. Drinking water and feed: A sudden change in or shortage of drinking water and feed quality, such as restricted water supply, even if only for 1-2 days, will at best stagnate the growth and weight gain of chicks within 7-14 days; if the water restriction lasts longer, it can cause a significant drop in productivity and even death. Therefore, it is very important to let chickens drink high-quality water. When feed quality changes suddenly or has an off odour, it can also markedly affect the feed intake of chickens.

2. Stocking density: Reasonable stocking density is very important in the broiler rearing process. Many farmers worry that a low density will easily waste chicken housing, but for fast-growing broilers, a reasonable stocking density can better enable the flock to achieve high uniformity. When stocking density exceeds the reasonable stocking density standard, the more severe the stress, the greater the impact on chicken productivity. At the same time, high stocking density can also lead to disease infection due to stress, such as staphylococcosis, chest, leg and claw injuries, poor development, and vices such as vent pecking.

3. Catching and beak trimming: Beak trimming and catching are both very strong stresses for chickens, and can affect feed utilisation and weight gain. In order to reduce the stress of beak trimming, the operation during beak trimming is required to be skilled and fast, and it should be carried out at as young an age as possible. Some people, in order to reduce one stress, carry out vaccination and beak trimming at the same time. This is not advisable, because doing so instead increases the degree of stress.

4. Chick transport: The transport, movement and long-distance shipping of chicks all consume the chicken's physical strength and water, and are a serious stress. Transport time should be shortened as much as possible, and after arrival the chicks should be given sufficient drinking water, with antibacterial drugs and vitamin additives added to the feed.

5. Vaccination: Although vaccination is an indispensable link in epidemic prevention measures, no matter which route of inoculation is used, it is a kind of stress. The vaccine entering the body and producing the immune process is also a kind of stress. If chicks are infected with Mycoplasma and are also given aerosol immunisation against Newcastle disease, it can cause chronic respiratory disease.

4. Disease and drug-induced stress. During chronic or latent infection with certain bacteria, viruses or internal and external parasites, because the body and these pathogens are in a relative balance, it becomes chronic or subclinical asymptomatic infection. If at this time other diseases are also contracted, or the climate and feeding management conditions worsen, then severe clinical symptoms can appear, causing huge losses.

When certain drugs are administered in excess, such as sulfonamide drugs, certain antibiotics, and drugs such as furazolidone and olaquindox being improperly administered, given in excess or used for a long time, in severe cases poisoning occurs, and in mild cases the synthesis of vitamins in the intestine is affected, thereby causing stress symptoms such as subcutaneous haemorrhage. Improper selection and use of certain disinfectants can also cause stress.