The use of antibiotics to maintain animal well-being, promote growth and improve efficiency has been practised for more than 50 years. However, as early as the 1950s, researchers identified concern on the development of resistant bacteria for the antibiotics streptomycin and tetracycline used in turkeys and broilers respectively. These findings laid the groundwork for agricultural officials to impose stricter regulatory parameters on the use of antibiotics in poultry feeds. Probiotics are live micro-organisms included in the diet of animals as feed additives or supplements. Commonly known as a direct-fed microbial, probiotics provide beneficial properties to the host, primarily through action in the gastrointestinal tract (GIT) of the animal. Supplementation of probiotics in the diet can improve animal health and performance, through contributions to gut health and nutrient use. For instance, supplementation of probiotics has been demonstrated to benefit farm animals in immune modulation, structural modulation and increased cytokine production, which positively affect the intestinal mucosal lining against pathogens. Bacillus subtilis has been a popular bacterium used within the industry and was shown to improve intestinal villus height. Increasing the villus height and structure of the crypts in the GIT allows for the improvement of nutrient digestion and absorption. Tight junctions maintain important defences against pathogenic bacteria and cellular homeostasis. Heat stress can be a major environmental challenge in the poultry industry. Heat stress causes the bird to fluctuate its internal core temperature beyond their comfort zone. To overcome such challenges, poultry will attempt to balance its heat production and dissipation through behavioural and physiological adaptation mechanisms.