The term "heat stress" is translated from the English heatstress. In layman's terms, heat stress can be referred to as high temperature, heat stress, or heat stress. In general, any room temperature above 27°C can be considered as heat stress.
Summer heat, high humidity, often appear on rainy days. The chicken's skin has no sweat glands, and the body is covered by feathers, so the chicken is not heat-resistant. The speed of heat flow from the bird itself 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. When the ambient temperature is high and the difference is small, the heat flow rate or heat loss is slower.
Another point is the degree of feathering. The more compact and thick the feathers grow, the worse the cooling effect is, mainly rely on the respiratory system to dissipate heat and regulate body temperature. If the ambient temperature is high, the humidity is high, the drinking water is insufficient, especially if the ventilation is poor, and the chicken body is difficult to dissipate heat, it is prone to heat stress, leading to metabolic and physiological disorders in the chicken body, thereby affecting the chicken's health and even causing suffocation. Gives a certain economic loss to chicken production.
In the temperature range of 10°C to 28°C, there is no apparent effect on the laying performance of the hen, but it cannot tolerate a sustained high temperature above 30°C. When shenwen is above 28°C, the chicken becomes hot and intolerant, showing mouth breathing, increased breathing, and breathing through the lungs to promote heat dissipation. At this time, it is common for hens to open their wings in order to expand the area of ​​surface heat dissipation and generate air convection to cope with high temperatures. Due to increased body heat, chickens instinctively reduce feed intake, so hens appear to have poor appetite and low feed intake. High-temperature heat stress can reduce the egg production rate of the hen, the egg weight is small, the egg shell is thin, and the broken egg rate increases.
The main harm of heat stress to laying hens
(I) Decline in feed intake
In the moderate temperature range of 15 °C to 27 °C, temperature and feed intake were positively correlated. When the temperature was above 27°C, temperature and feed intake were negatively correlated. For every 1°C increase above 27°C, feed intake decreased by 1.5% to 2.0%. Therefore, as the temperature rises, feed intake will decline rapidly.
(b) Eggs become lighter
For every 1°C increase above 27°C, the egg weight will fall by 0.2g to 0.3g due to a decrease in feed intake and insufficient intake of protein and heat energy.
(c) Thinned eggshells, increased broken egg rate
For every 1°C increase above 27°C, the unacceptable egg increases by 1%.
There are two main reasons: one is the reduction in the intake of calcium, phosphorus and vitamin D; the other is the metabolic cause, in the high temperature conditions, the chicken's thyroid hormone secretion is reduced. The level of thyroid hormone directly affects the metabolic rate, and metabolic rate is one of the important factors affecting chicken egg production performance, so the high temperature causes a decline in feed intake, which in turn leads to weight loss, eventually causing a decrease in egg production and egg weight. Eggshell quality deteriorated. Therefore, the key technical measure for keeping laying hens in summer is to solve the problem of cooling.
Pathological changes
Chicken pale, soft, semi-ripe, black blood, blood leaking in the chest and abdomen, abdominal fat hemorrhage, hepatomegaly hemorrhage, pulmonary edema, hemorrhage, congestion, severe black, loose heart muscle, ventricular dilation, follicular hyperemia of laying hens Ovarian congestion, uterine retention eggs; glandular stomach wall thinning; severe intestinal edema, intestinal mucosa off, there are thin contents; cerebral hemorrhage.
The control of summer heat stress
(I) Reducing stocking density
Lower flock density can help reduce this heat burden
(b) Reduction of radiant heat
1 Use light-colored materials for roofs and interior wall surfaces. 2 insulation. 3 shade. 4 Plant lawns. 5 The concrete floor cannot be laid around the house.
(iii) Implementation of evaporative cooling
1. Available simple roof sprinkler. 2. Install the aerosol nozzle indoors.
(d) Strengthen ventilation and air flow rate
Ventilation and cooling: In the houses with ventilation facilities, the operating time of the fans must be increased and the ventilation interval should be shortened. Wet curtains should be hung at the air inlet to reduce the temperature of the house. In a naturally ventilated house, all vents should be opened for maximum ventilation.
(E) Nutrition regulation
Chicken - eat because of "energy."
During the hot summer days, the feed intake of chickens is reduced. Only by increasing the protein levels in the diet as appropriate, and ensuring the balance of amino acids, it is possible to meet the protein requirements of the laying hens. Otherwise, the egg production will be affected due to insufficient protein. The protein content of laying hens in hot season should be increased by 1-2% compared with other seasons, reaching over 18%. Therefore, it is necessary to increase the amount of feeds for cakes, such as soybean meal and cotton cakes, in the compound feed, by no less than 20% to 25%. Energy per ton of feed plus fat 10 kilograms ~ 20 kilograms, protein to increase plant protein, increase methionine content (20%). Reserve hens should ensure their proper body weight and body condition, add sodium bicarbonate and increase the amount of vitamins. Changes in diet should be carried out as early as possible before the onset of heat stress, and gradually adjust to adapt the chicken.
(6) Adjust feeding time
Feed as much as possible during the cool time of the day between 4 AM and 5 AM, 10 AM and 11 AM, and 6 AM and 7 AM.
Do not feed during high heat hours, reducing the amount of flock activity and keeping the birds in a quiet state. To avoid noise interference, feeding, feeding, cleaning, licking eggs and other actions should be light to prevent frying. After vertigo occurs, soak the chickens in cold water and transfer them to a cool, ventilated place.
(7) Non-negligible drinking water
Water is a very critical nutrient. Summer water consumption has doubled over other seasons. In summer, drinking water should not only be fresh, adequate, hygienic, and easy to drink. In particular, the water temperature should be as low as 27°C.
On a hot day, the chicken's drinking water is significantly increased. The purpose is to obtain temporary coolness by drinking more water. The amount of water the chicken drinks depends mainly on feed consumption and temperature. According to tests, the amount of water consumed by the chicken at the temperature of 15.6°C was 1.8 times that of the feed. 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, water shortages are not allowed under any circumstances in the summer. If it is automatic water supply, be sure to keep the water flowing. If you use a water dispenser or a general sink to supply water, you must not empty the tank. Keep your drinking water clean and clean. Excessive drinking of chicken will make the chicken droppings thinner and deteriorate the hygiene environment in the house. Using a nipple drinker in caged chickens is a good measure to reduce water consumption, ensure normal water supply, and eliminate chicken manure.
(8) Disinfection with chicken
Disinfection with chicken spray, 2 to 3 times a week with chicken disinfection, can use high-efficiency and low toxicity drugs, while doing a good job within the house fly control, mosquito control, pest control work.
(9) Timely removal of manure
There are scrapers to clear once or twice a day.
Control Program (1) Adding Sodium Bicarbonate
High temperatures in summer can easily cause metabolic acidosis in chickens. Adding enough sodium bicarbonate to feed can eliminate this effect and balance the blood's buffer. Tests have shown that when chickens are heat-stressed, 0.3% to 0.4% sodium bicarbonate is added to feed, and the flock disability rate is reduced by half compared to 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.
The use of sodium bicarbonate in chicken production should pay attention to two points: (1) All drugs or additives that are easily destroyed by alkaline, such as vitamin B1, vitamin B2, vitamin C and folic acid, and antibacterial and organic acids, should be avoided and carbonated Hydrogen and sodium are used together. (2) Use proper amount of sodium bicarbonate. Excessive sodium bicarbonate can cause alkalosis, and should reduce the amount of salt to avoid excessive intake of sodium in chickens.
(B) Add Vitamin C
In laying hens, VC is involved in the formation of collagenous tissue, which promotes eggshell formation. Under high temperature conditions, it prevents the formation of a collagen matrix on the eggshell, and calcium carbonate is deposited on the collagen matrix. Therefore, by supplying VC, the egg laying rate 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 UV, high temperature will greatly reduce the stability of VC, so VC should be protected from light and high temperature; VC can be decomposed by the oxidation of copper, iron and other ions, in the use, should pay attention to copper and iron ions in the feed Concentration; VC bogey and sulfa drugs, tetracycline drugs used simultaneously; VC bogey and alkaline substances used simultaneously.
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