The term "heat stress" is translated from English heatstress. In general, heat stress can be called high temperature, thermal stress or heat stress. Generally, room temperature above 27 ° C can be considered as heat stress.

Summer is hot, high humidity, and often rainy. The skin of the chicken has no sweat glands, and the body is covered by feathers, so the chicken is not resistant to high temperatures. The speed at which the heat of the chicken itself flows to the surrounding air depends on two points:

One is the relative difference between the temperature of the chicken body and the ambient temperature. When the difference is large, the heat flow rate or heat loss is faster, the ambient temperature is high and the difference is small, and the heat flow rate or heat loss is slower.

Another point is the degree of feathering. The more compact and dense the feathers are, the worse the heat dissipation is, mainly relying on the respiratory system to dissipate heat and regulate body temperature. If the external environment temperature is high, the humidity is high, the drinking water is insufficient, especially the ventilation is poor, and the chicken body is difficult to dissipate heat, it is easy to cause heat stress, which causes the metabolism and physiological function of the chicken body to be disordered, thereby affecting the health of the chicken and even causing suffocation and death. It brings certain economic losses to the production of chickens.

The temperature range of 10 °C ~ 28 °C has no obvious effect on the laying performance of hens, but can not endure the continuous high temperature above 30 °C. When the temperature is above 28 °C, the chicken becomes hot and intolerable. It is characterized by breathing in the mouth, increasing the number of breaths, and discharging the moisture in the lungs through breathing to promote heat dissipation. At this time, the hens often open their wings to expand the surface area of ​​the body surface and generate air convection to cope with the high temperature. Due to the increase in body heat, the chicken instinctively reduces the intake of feed, so the hen appears to have poor appetite and less feed intake. High temperature heat stress can reduce the laying rate of hens, the egg weight is small, the eggshell is thin, and the egg breaking rate is increased.

The main hazard of heat stress on laying hens

(1) Decline in feed intake

Temperature is positively correlated with feed intake over a moderate temperature range of 15 °C to 27 °C. When the temperature is above 27 °C, the temperature is negatively correlated with the feed intake. For every 1 °C increase above 27 °C, the feed intake decreases by 1.5% to 2.0%. Therefore, as the temperature rises, the feed intake will drop rapidly.

(2) The egg weight becomes lighter

When the temperature rises by 1 °C above 27 °C, the egg weight will drop by 0.2 g to 0.3 g, which is caused by a decrease in feed intake and insufficient intake of protein and heat.

(3) The eggshell is thinner and the egg breaking rate is increased.

For every 1 °C increase above 27 °C, unacceptable eggs will increase by 1%.

There are two main reasons: one is the reduction of calcium, phosphorus and vitamin D intake; the other is the metabolic cause, the chicken's thyroxine secretion is reduced under high temperature conditions. The level of thyroxine directly affects the rate of metabolism, and the metabolic rate is one of the important factors affecting the performance of laying eggs. Therefore, high temperature causes a decrease in feed intake, which in turn leads to weight loss, which ultimately leads to lower egg production and egg weight. The quality of the eggshell deteriorated. Therefore, the key technical measure for laying hens in summer is to solve the problem of cooling.

Pathological changes

Chicken is pale, soft, semi-ripe, black blood, blood exudation in the chest and abdomen, abdominal fat bleeding, hepatomegaly hemorrhage, pulmonary edema hemorrhage, congestion, severely black, soft heart, ventricular dilatation, egg follicle congestion The ovary is congested, the uterus has retained eggs; the glandular stomach wall becomes thin; the intestinal tract is highly edematous, the intestinal mucosa falls off, and there is a thin content inside; cerebral hemorrhage.

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Control of heat stress in summer

(1) Reduce the stocking density

Lower flock density can help reduce this heat burden

(two) reduce radiant heat

1 Use light-colored materials for the roof and the inner wall surface. 2 insulation. 3 shade. 4 planting lawns. 5 No concrete floor can be laid around the house.

(3) Implementing evaporative cooling

1. A simple roof sprinkler can be used. 2. Install an aerosol nozzle indoors.

(4) Strengthen ventilation and air flow rate

Ventilation and cooling: For houses with ventilation facilities, increase the running time of the fan, shorten the ventilation interval, and hang the wet curtain at the air inlet to reduce the temperature of the house. Naturally ventilated houses are to open all vents for maximum ventilation.

(5) Nutritional regulation

Chicken - eat because of "can".

In the summer heat, the feed intake of chickens is reduced. Only by increasing the protein level in the feed as appropriate, and ensuring the balance of amino acids, it is possible to meet the protein needs of the laying hens. Otherwise, the egg production will be affected by insufficient protein. The protein content of the laying hens in the hot season should be increased by 1 to 2 percentage points compared with other seasons, reaching more than 18%. Therefore, it is necessary to increase the amount of cake-based feed such as soybean meal and cotton kernel cake in the compound feed, and the dosage is not less than 20% to 25%. The energy is 10 kg to 20 kg per ton of feed, and the protein is mainly plant protein, which increases the methionine content (20%). Reserve hens should be properly maintained in body weight and body condition, add sodium bicarbonate and increase the amount of vitamins. Changes in the diet should be carried out early before the onset of heat stress, and gradually adjusted to adapt the chicken.

(6) Adjusting the feeding time

Try to feed in the cool time of the day from 4:00 am to 5:00 am, from 10:00 am to 11:00 am, from 6:00 am to 7:00 pm

It is better to not feed during high heat, reduce the activity of the flock, and keep the birds in a quiet state. Avoid noise interference, feeding, watering, cleaning, licking eggs, etc. should be light to prevent the group. After vertigo, soak the chicken in cold water and transfer to a cool, ventilated place.

(7) Non-negligible drinking water

Water is a very critical nutrient, and water consumption in summer is doubled compared to other seasons. In summer, drinking water should not only be fresh, adequate, hygienic, and easy to drink. Especially, the water temperature should be lowered to a normal temperature below 27 °C.

On hot days, the amount of water consumed by the chickens increased significantly, and the purpose was to obtain temporary cooling by drinking more water. The amount of water consumed by the chicken depends mainly on the feed consumption and temperature. According to the test, the drinking water of the chicken at 15.6 °C is 1.8 times of the feed consumption. It is 2 times at 21.1 °C, 2.8 times at 26.6 °C, 4.9 times at 32.2 °C, and 8.4 times at 37.8 °C. Therefore, there is no shortage of water in any situation in the summer. If it is automatic water supply, be sure to keep the water flowing smoothly. If you use a water drinker or a general water tank, you must not empty the tank. Keep the drinking water clean and clean. Excessive drinking water from chickens can make chicken manure thinner and worsen the sanitation environment. The use of nipple drinkers in caged chickens is a good measure to reduce water consumption, ensure normal water supply and eliminate chicken manure.

(8) Disinfecting chicken

Disinfect with chicken spray, disinfection with chicken 2 times to 3 times a week, you can use high-efficiency and low-toxic drugs, and at the same time do a good job in killing, killing mosquitoes and killing insects.

(9) timely defecation

It is necessary to clear the manure machine once or twice a day.

Control plan (1) Add sodium bicarbonate

High temperature in summer can easily cause metabolic acidosis in chickens. Adding enough sodium bicarbonate to the feed can eliminate this effect and balance the blood buffer. Tests have shown that when chickens are under heat stress, 0.3% to 0.4% sodium bicarbonate is added to the feed, and the flock rejection rate is reduced by half compared with the absence of sodium bicarbonate. The acid-base balance in chickens is mainly regulated by a buffer system, and sodium bicarbonate is the most important part of the buffer system.

In the production of chickens, sodium bicarbonate should pay attention to two points: (1) Any drugs or additives that are easily destroyed by alkali, such as vitamin B1, vitamin B2, vitamin C and folic acid, antibacterials and organic acids, should be avoided and carbonated. Mix sodium hydride. (2) Use an appropriate amount of sodium bicarbonate. Alkali poisoning can occur due to excessive sodium bicarbonate, and the amount of salt should be reduced accordingly to avoid excessive sodium intake by chickens.

(two) add vitamin C

In the laying hens, VC participates in the formation of collagenous tissue, thereby promoting the formation of eggshells. Under high temperature conditions, it prevents the formation of collagen matrix on the eggshell, and calcium carbonate deposits on the collagen matrix. Therefore, by replenishing VC, the laying rate of the laying hen can be increased, and the thickness of the eggshell can be increased. Reduce heat stress: add 1 g / 100 kg of feed.

VC is very sensitive to ultraviolet light. High temperature will greatly reduce the stability of VC. Therefore, VC should be protected from light and high temperature. VC can be decomposed by oxidation of copper and iron. When using, attention should be paid to copper and iron in feed. Concentration; VC avoids simultaneous use with sulfa drugs and tetracyclines; VC avoids simultaneous use with alkaline substances.