In the aquaculture industry, high temperatures combined with high humidity are among the most damaging environmental factors, often leading to heat stress syndrome in livestock and poultry. Heat stress significantly weakens the immune system by reducing the levels of immunoglobulins in the blood and decreasing the number of lymphocytes. This results in a decline in macrophage phagocytic activity, making animals more prone to infectious diseases. As a result, heat-stressed animals become more vulnerable to illness. Modern high-performance breeds, while producing better yields, tend to have weaker resistance to heat stress. Severe heat stress can even lead to sudden deaths in these high-performing animals, causing significant economic losses. To help farmers manage this issue, we will discuss several strategies to improve the internal environment of livestock and poultry.
1. Adjusting Dietary Nutrition Appropriately
(1) Modifying Protein and Amino Acid Levels: Reducing dietary protein while maintaining essential amino acid levels can enhance growth and survival rates. For broilers, adding D-methionine is beneficial, while pigs can benefit from using synthetic lysine instead of natural protein sources.
(2) Increasing Energy Content: The energy concentration in feed should be adjusted to minimize heat production. Fat, which generates the least heat, can be used to replace part of the carbohydrates, increasing energy density and improving the animal's ability to cope with heat stress. Typically, 2% to 3% fat is added to the diet.
(3) Managing Mineral Content: During heat stress, the excretion of potassium, sodium, zinc, and molybdenum through urine increases, along with higher fecal excretion of calcium, manganese, selenium, and copper, while magnesium and phosphorus levels decrease. When ambient temperature exceeds 20°C, the calcium, phosphorus, sodium, and chlorine content in feed should be increased by 1.5% for each 1°C rise to meet the body’s needs.
2. Using Anti-Stress Additives to Alleviate Heat Stress
(1) Supplementing Vitamins C and E: Heat stress increases cortisol secretion, which raises the need for vitamin C. At the same time, the body’s ability to synthesize vitamin C decreases, making supplementation essential. Vitamin C can be added to feed or drinking water—100–150 grams per ton of feed for broilers, and similar amounts for pigs. In drinking water, 1 gram per liter is recommended, with continuous access. Vitamin E also helps combat heat stress by supporting immune function. Adding 200–300 mg/kg of vitamin E to broiler diets improves T3 and T4 levels, while increasing layer diets to 35–50 IU boosts egg production by 1.5% to 5.5%. For pigs, 200 IU/kg of vitamin E can effectively reduce heat stress effects.
(2) Balancing Electrolytes and Acid-Base Levels: Studies show that adding sodium chloride, potassium chloride, and sodium bicarbonate to feed or water helps restore acid-base balance, enhancing performance. Sodium bicarbonate at 0.5% is commonly used. During heat stress, respiratory rate increases, leading to lower CO2 and HCO3- levels, raising blood pH and potentially causing respiratory alkalosis. Adding acidifiers like lactic acid,
Citric Acid, or fumaric acid to feed helps regulate pH, mitigating the negative impacts of heat stress.
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