Magdi Mohamed Mashly

BEFORE one considers the relationships between responses to exogenous ACTH or glucocorticoid administration and responses to environmental stimuli, it is important to consider whether birds from varying genetic backgrounds respond similarly to these exogenous materials.

Thiessen and Nealy (1962), using eosinophil count and adrenal weight as response criteria to handling stress, reported that the pattern of response for one of five inbred strains of mice could not be used to predict the pattern for the others. Highly significant differences in changes of plasma corticosterone levels resulting from electric shock treatments were found among four inbred mouse strains by Levine and Treiman (1964).

Genetic differences in thiouracil-induced hypothyroidism (El-Ibiary and Shaffner, 1951; Shaklee and Shaffner, 1955), and in assay sensitivity to gonadotropins (Siegel and Siegel, 1964a, b) have been observed; however, little has been reported concerning genetic influences upon the response of the avian pituitary-adrenal cortical system to exogenous hormone stimulation. . . .

The body weights of 7 to 9 month-old White Leghorn males were observed by Lamoreux (1943) to be significantly greater when light was restricted to less than 9 hours per day. Siegel et al. (1961) reported significantly heavier body weights and better feed conversion in White Leghorn pullets at 8 weeks of age when restricting light to 6 hours per day compared to 14 hours of light per day. In a study with broiler chickens, Moore (1957) found that faster growth was obtained up to 3 or 4 weeks of age with continuous light although feed efficiency was slightly better with less light throughout the growing period. A series of experiments reported by Shutze et al. (1960) indicated that birds exposed to continuous light were superior in body weight gain to those on the other light regimes with the exception of one experiment in which chick growth response to 2 . . .