Invisible Killer in High Temperatures- Heat Stress in Chickens Ⅰ

Invisible Killer in High Temperatures- Heat Stress in Chickens Ⅰ

Preface

In the intensive and large-scale breeding of modern animal husbandry, due to a series of unavoidable factors such as limited feeding conditions, chickens are often subjected to various stresses during the production process, such as vaccine injection stress, cold stress, heat stress, etc. Stress, beak trimming stress.

In recent years, the global greenhouse effect has continued to intensify, the high temperature season has continued to lengthen, and summer temperatures have continued to rise. Heat stress has become a major stress factor affecting animal production. (SEJIAN et al., 2018)

The core of the harm caused by stress to animals is that stress causes intestinal microecological disorders and the proliferation of harmful bacteria, leading to the release of large amounts of bacterial endotoxins, destroying the intestinal mucosal barrier, causing a large amount of endotoxins to invade the blood, and destroying the body's immune function.

It is estimated that in China, poultry production loses US$2.7 billion annually due to various stresses, especially heat stress (LinHai et al., 2012). Heat stress also costs poultry production an average of US$128 million to US$165 million per year in the United States (StPierre, 2013).

The magnitude of heat stress in chickens depends on factors such as age, the maximum temperature of the environment, the duration of high temperature, the speed of temperature change, and the relative humidity of the air. If the external environment has high temperature, high humidity, insufficient drinking water, especially poor ventilation, and it is difficult for the chicken body to dissipate heat, heat stress will easily occur.

Heat stress is a non-specific response produced by the body to maintain body homeostasis due to body heat imbalance caused by high temperature environment.

Heat stress in chickens is the result of the interaction of different factors such as ambient temperature, humidity and radiant heat. Chickens have a strong metabolism, which leads to high body temperature. The whole body is covered with feathers, the skin has no sweat glands, and the heat dissipation is poor, making it easy to suffer from heat stress. Hot and high temperatures in summer often lead to endocrine abnormalities, reduced appetite, slow growth and development, and reduced immunity and disease resistance in chickens, which in turn causes increased morbidity and mortality, ultimately bringing huge consequences to modern intensive chicken production loss. Especially at the stage when broiler chickens are about to be put on the market, if they suffer from stress during breeding or transportation and cause illness or death, all the previous investment in breeding will be wasted.

Chicken liver is extremely sensitive to heat stress, and oxidative stress mediated by heat stress is an important way to damage liver health. Liver damage causes a decrease in feed digestion, absorption and utilization, and a significant increase in the incidence of ascites in broilers and fatty liver in laying hens.

Once heat stress occurs, it means that the temperature change has exceeded the upper limit of the body's self-regulation and cannot maintain the stability of the internal environment. According to Van't Haff's law, for every 1°C increase in body temperature, the speed of chemical reactions will increase by 1 to 2 times. Heat stress will cause the body temperature to rise, and the rise in body temperature will increase the body's heat production, thereby aggravating heat stress. The occurrence of stress, this vicious cycle will aggravate the damage of heat stress to the body.

Effect of heat stress on broiler performance

The main effects of heat stress on broiler performance include:

It reduces the feed intake and feed utilization of chickens, reduces the growth performance of chickens, increases breeding costs, and also affects the muscle quality of broiler chickens and even leads to death.

Zhong Guang et al. conducted cyclic heat stress treatment on yellow-feather broilers and measured their growth performance. They found that cyclic heat stress can significantly accelerate the respiratory frequency of yellow-feather broilers, reduce the average daily feed intake and average daily weight gain, and increase feed meat at the same time. Compare.

Wang Qijun et al. used AA broiler chickens as the research object and conducted heat stress treatment under high temperature conditions of 35°C. The research found that:

Compared with the room temperature ad libitum feeding group, the average daily feed intake of the heat stress group decreased by 44.91%, the average daily weight gain decreased by 65.67%, and the feed-to-meat ratio increased significantly. Comparing the ratio of average daily feed intake and average daily weight gain, it can be found that the impact of heat stress on average daily weight gain not only comes from the decrease in average daily feed intake, but may also have a negative impact on the physiological functions of AA broilers.

The impact of heat stress on the growth performance of broiler chickens is related to the physiological state, breed, gender and other factors of the broiler chickens. The mortality rate of broilers during the growth period caused by heat stress is significantly lower than that of chicks. The physiological functions of chicks are less complete than those of broilers in the growth period. As they age, their physiological functions gradually improve, thereby reducing the body's sensitivity to heat stress.

Breeding technology has enabled modern fast-growing commercial broilers to grow faster, but it has also inevitably increased the sensitivity of commercial chickens to heat stress. Compared with fast-growing commercial broilers, slow-growing local breed broilers or hybrid chickens have better resistance to environmental stress. Osman et al. found that heat stress caused a greater decrease in weight gain in roosters than in hens.

Effect of heat stress on production performance of laying hens

The main symptoms of laying hens and breeder chickens are: Decreased feed intake, decreased egg production rate, smaller egg size, production of inferior eggs (broken shell eggs, soft shell eggs and thin shell eggs); affects the sexual maturity of hens, delaying the age of onset of production; fatty liver and hemorrhage combined The incidence of symptoms increases.   The fertilization rate and hatching rate of breeding hens are reduced, thus affecting the hatching performance of egg breeders; the male breeding chickens show poor semen quality, reduced semen volume, and reduced fertilization rate. Heat stress can also affect the immune function of laying hens, reducing their resistance and increasing morbidity and mortality.