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Abstract
1. Cockerels from meat‐type (MT) and Leghorn (LG) stocks were fed on diets containing 0, 20, or 30 mg corticosterone/kg from 1 to 22 d after hatching.
2. Within MT and within LG stocks, responses to dietary corticoster‐one inclusion rates were similar; however, patterns differed beween these major classes resulting in stock X diet interactions.
3. Traits responding to different inclusion rates of corticosterone in a dissimilar manner for MT and LG chickens included: immunorespon‐siveness, body weight, efficiency of food utilisation, feathering; relative weights of liver, spleen, bursa, testes, breast and abdominal fat pad, as well as the proportion of liver lipid.
4. No differential responses occurred for relative adrenal weight, plasma xanthophyll concentrations, proportion of breast lipid and abdominal fat, or surface and cloacal temperatures.
5. Results indicated genetic differences in thresholds for response to corticosterone and in degree of response once thresholds were reached. Within populations, sensitivities varied between target organs.
