Heat stress is one of the major environmental stressors in the poultry industry resulting in substantial economic loss. Heat stress causes several physiological changes, such as oxidative stress, acid-base imbalance, and suppressed immunocompetence, which leads to increased mortality and reduced feed efficiency, body weight, feed intake, and egg production, and also affects meat and egg quality. Several strategies, with a variable degree of effectiveness, have been implemented to attenuate heat stress in poultry. Nutritional strategies, such as restricting the feed, wet or dual feeding, adding fat in diets, supplementing vitamins, minerals, osmolytes, and phytochemicals, have been widely studied and found to reduce the deleterious effects of heat stress. Furthermore, the use of naked neck (Na) and frizzle (F) genes in certain breed lines have also gained massive attention in recent times. However, only a few of these strategies have been widely used in the poultry industry. Therefore, developing heat-tolerant breed lines along with proper management and nutritional approach needs to be considered for solving this problem. Thus, this review highlights the scientific evidence regarding the effects of heat stress on poultry health and performances, and potential mitigation strategies against heat stress in broiler chickens and laying hens.

The chicken oviduct is a unique organ in which ovulated yolk transforms into a complete egg. Ovarian hormones induce the cellular and biochemical changes in the oviducts during the egg formation and oviposition. Estradiol regulates the folliculogenesis, accumulation of yolk in the follicles, ovulation, and development of oviducts. Estradiol also induces glandular development and expression of the genes responsible for egg white proteins. Progesterone induces the ovulation of yolk from the ovary, and development of oviductal glands. In addition, several genes are spatiotemporally expressed in the magnum for albumen synthesis and deposition around the yolk, in the isthmus for shell membranes synthesis, and in the uterus for eggshell biomineralization. This chapter highlights the involvement of hormones, genes/proteins, and their interaction for egg formation in the oviduct of laying hens.