Using major genes to mitigate the deleterious effects of heat stress in poultry: an updated review.

Acceleration of global warming has emerged as one of the biggest environmental challenges facing poultry farming. In heat stressed flocks, massive mortality rates and substantial damage to productive performance (eggs and meat) are commonly noticed. Because birds do not have sweat glands, they cannot tolerate high temperatures, especially when combined with high humidity. Under this harsh environmental condition, the birds reduce their feed consumption to decline metabolic energy rate. At an ambient temperature of more than 26°C, the bird increases panting and reduces metabolic rate to get rid of the body's heat increment. There are many scenarios that can be followed to alleviate the adverse effects of heat stress. Management practices, nutritional modification, and/or feed additives are frequently used in poultry farms. However, introducing major genes such as naked neck (Na), frizzle (F), slow feathering (K), and dwarf (dw) could be adopted as a significant solution to improve productive performance in birds raised under high environmental temperatures. The birds carrying these mutations gain popularity owing to their ornamental appearance and highly productive performance at high temperatures. Moreover, utilizing dwarf gene in broiler breeders as a dam line improves adaptability, survivability, and hatchability in flocks kept in hot climates. At hatch, the sex-linked slow feathering mutation has been widely used for wing sexing in some egg-type breeds. The potential use of major genes as a breeding strategy to enhance heat tolerance in chickens has been extensively reviewed.

Genetic improvement of egg laying traits in Fayoumi chickens bred under conditions of heat stress through selection and gene expression studies.

Thermal stress has been shown to result in decreased egg production, decreased eggshell quality, and ultimately millions of dollars in losses to the industry. Therefore, there are many factors to consider when implementing genetic selection programs aimed at improving egg production under tropical conditions. So, trial is trying to improve the productivity and eggshell quality traits of the Fayoumi chicken under high ambient temperatures via selection programs and gene expression. In the present study, day-old Fayoumi chicks were raised either under normal temperature (control) or conditions of thermal stress (the heated group). At 35 weeks, male and female chickens from the control group were mated randomly and females selected for higher egg production and eggshell strength were mated to male siblings to obtain the progeny of the first generation (F1). F1 birds were further selected and mated to obtain the progeny of the second generation. Our results show that egg production and eggshell strength traits improved over successive generations via selection under conditions of heat stress. Furthermore, the reduction in egg production and eggshell strength as a result of heat stress declined from one generation to the next in birds selected for good heat tolerance, and an inverse relationship was observed between the OC-17 and eggshell strength. Additionally, levels of HSP90 and gene expression increased in the two successive generations, indicating that both productivity and heat tolerance were enhanced due to selection in birds raised under conditions of thermal stress. Moreover, generation exerted an important effect on this trait. Thus, desirable traits such as improved heat tolerance in producing lines were observed in Fayoumi chickens exposed to conditions of thermal stress via selection. Therefore, modern advances in studies of poultry breeding and genetics, such as gene expression studies, should be examined.

Expression levels of HSP70 and CPT-1 in three local breeds of chickens reared under normal or heat stress conditions after the introduction of the naked neck gene.

The naked neck gene was introduced by crossbreeding into Egyptian breeds to improve body weight. Expression levels of HSP70 and CPT-1 were used to assess the heat tolerance of three Egyptian local breeds (Fayoumi, Dandarawi and Sinai) with and without the naked neck gene and under normal and heat stress conditions. There were two genotypes from each breed that had the same genetic origin (the naked neck and normal plumage genotypes). For each genotype, chicks were divided into two groups, a control group and a treated group. Chicks in the treated group were subjected to heat stress (40 °C) for four hours when they were between 3 and 5 days old. This treatment was associated with a highly significant increase in HSP70 and CPT-1 gene expression for the Dandarawi breed compared to the levels in the Fayoumi and Sinai breeds. Moreover, the introduction of the naked neck gene into these local breeds caused marked increases in CPT-1 gene expression, but these increases did not significantly differ among different naked neck genotypes. Therefore, it could be concluded that the Dandarawi breed exhibited the best heat tolerance, followed by the Sinai breed, whereas the Fayoumi breed was inferior in this respect. Furthermore, the naked neck gene improved heat tolerance by increasing HSP70 gene expression rather than only by reducing feather cover. The results obtained recommended using the Sinia naked neck chicken as a male line in commercial parent stock to produce broiler chicks adapted to the hot and warm climates.

Prediction of Eggshell Ultrastructure via Some Non-destructive and Destructive Measurements in Fayoumi Breed.

Possibilities of predicting eggshell ultrastructure from direct non-destructive and destructive measurements were examined using 120 Fayoumi eggs collected from the flock at 45 weeks of age. The non-destructive measurements included weight, length and width of the egg. The destructive measurements were breaking strength and shell thickness. The eggshell ultrastructure traits involved the total thickness of eggshell layer, thickness of palisade layer, cone layer and total score. Prediction of total thickness of eggshell layer based on non-destructive measurements individually or simultaneously was not possible (R(2) = 0.01 to 0.16). The destructive measurements were far more accurate than the non-destructive in predicting total thickness of eggshell layer. Prediction based on breaking strength alone was more accurate (R(2) = 0.85) than that based on shell thickness alone (R(2) = 0.72). Adding shell thickness to breaking strength (the best predictor) increased the accuracy of prediction by 5%. The results obtained indicated that both non-destructive and destructive measurements were not useful in predicting the cone layer (R(2) not exceeded 18%). The maximum accuracy of prediction of total score (R(2) = 0.48) was obtained from prediction based on breaking strength alone. Combining shell thicknesses and breaking strength into one equation was no help in improving the accuracy of prediction.