Fig. 4.

In ovo feeding to thermally manipulated embryos increases toll-like receptors and growth hormone release and decreases the gene expression of heat shock proteins (HSP) in hatchlings. The diagram is drawn based on the articles (Elnesr et al., 2019; Elwan et al., 2019). Embryonic thermal manipulation during mid-term incubation and in ovo supplementation during late-term incubation may enhance hatching performance and reduce oxidative stress parameters in hatchlings. Such chickens are more resistant to heat stress as they possess lower oxidation and stress parameters during rearing conditions. In parentheses are examples of thermal manipulation or in ovo injection.