Today in India, poultry is one of the fastest growing segments of the agricultural sector. Heat stress is a great challenge for poultry farmers in hot climates, resulting in significant economic losses in the poultry business. Heat stress occurs when the ambient temperature surpasses the comfort zone (16–25°C) for poultry species and/or when an individual’s ability to remove heat exceeds its ability to generate heat. As a result of global warming, high temperatures have recently emerged as one of the major stresses affecting the poultry business globally. Modern poultry species have become substantially more vulnerable to prolonged heat stress, according to recent studies. In addition to improving environmental conditions, nutritional management is beneficial to partially mitigate the harmful effects of heat stress on birds. These efforts include providing diets with enhanced energy density, adding salts, probiotics, antioxidant vitamins and minerals to heat-stressed chicken. To alleviate the detrimental effects of heat stress in poultry, probiotics, prebiotics and synbiotics have recently been added to their diets.
Heat stress compromises gut integrity and function by disrupting intestinal microbiota balance, mucus layer and epithelial tight junctions. This weakening of the intestinal barrier allows the pathogenic bacteria’s and toxins to enter the host body more easily and triggers the acute pro-inflammatory immune activities. Acute heat stress (30°C for 24 hours) affects the intestinal conformation and gut microbial population, eventually increasing the chance of Salmonella attachment, according to the previous researches. Supplementing commensal bacteria to promote gut health is one way, for preventing these negative consequences of heat stress.
Probiotics are the mixture of useful live micro-organisms such as bacteria (Bacilli, Streptococci, Bifidobacteria and Lactobacilli), fungi (Aspergillus) and yeast cultures (strains of Candida and Saccharomyces),which are used as feed supplement to enhance the intestinal health, poultry performances and the immune responses. Probiotics can correct the defective villus-crypt structure of heat-stressed birds by regulating the corticosterone levels and unnecessary release of proinflammatory agents, which causes damage to intestinal tissue and increase intestinal permeability.
Many recent studies showed that the probiotics alleviate the oxidative damage caused by heat stress in poultry. But in few studies, probiotic (Protexin® Boost) treatment was found to increase the serum uric acid levels in heat stressed birds. So, considering the fact that uric acid is an important antioxidant, raised levels of uric acid can be a part of probiotics mechanism of action in eliminating the oxidative damage occurred in heat stressed birds. The broilers have improved growth rate, feed conversion ratio and immune responses on addition of probiotics to their feed. In another study, enhanced feed intake and daily weight gain, improved bodyweight and decreased mortality rate in harsh environmental conditions was observed on addition of yeast culture in broiler diets. Moreover, the acute heat stress damages the gut integrity and represses the immunity in broilers, whereas in case of laying hens major deficiency in structure of gastrointestinal tract and morphology of villi was observed along with poor intestinal integrity. So due to the high sensitivity of poultry to the environmental changes, it is therefore beneficial to supplement poultry diets with increased levels of probiotics.
Additionally, Bacillus subtilis (aerobic bacterium) increases the surface area of intestinal absorption and fosters the growth and multiplication of probiotics including Lactobacillus, Bacillus, Aspergillus awamori, Bifidobacterium and yeasts. Probiotics have been shown to play a physiological function in improving the antioxidant defence system in broiler chickens by activating the enzymatic antioxidants (such as SOD and GSH-Px) and improving the reaction to hydroxyl radicals, which improves the biological macromolecules’ resistance to oxidation. According to recent studies, adding dietary probiotics to broilers under prolonged heat stress, improved the quality of their skeletal muscles and raised the weight of their breast meat. Another study revealed that the lactic acid released by Lactobacilli (in probiotics) may promote improved absorption of Calcium and phosphorus from the digestive tract along with their decreased excretion. Ultimately it contributes in decreasing probable pollution caused by hen’s manure. Additionally, feeding probiotic-supplemented meals to laying quails resulted in considerably higher egg weight, quantity and mass. Probiotics also contributes in decreasing total lipid concentration and yolk cholesterol levels. Therefore, it is crucial to note that dietary probiotic supplementation may contribute to improved nutritional absorption, defense against pathogens and immunity enhancement, which ultimately leads to improved performance and disease resistance in chicken exposed to heat stress.
Heat stress has lately emerged as a serious threat to poultry production in India as a result of rising global temperatures. Heat stress can affect poultry’s physiology, immunology and microbiology, which can ultimately affect the bird’s performance. Therefore, probiotics are found as extremely beneficial in alleviating negative consequences of heat stress in poultry by enhancing the gut microflora, physiological conditions, immune system and birds performance. Probiotics should be used cautiously though, as some studies found little benefit.
Dr. Jasleen Kaur(Ph.D scholar)
Department of Veterinary Medicine,
Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana-141004