Haematology and blood composition at two ambient temperatures in genetically fat and lean adult broiler breeder females fed ad libitum or restricted throughout life

1. Genetically fat and lean adult broiler breeder females were fed ad libitum or restricted throughout life. At one year of age, comparisons of blood viscosity and haematology and changes in blood chemistry after exposure to thermal stress were conducted. 2. Whole blood viscosity was more than twice as high, and plasma triglyceride and haemoglobin concentrations were over 30% higher in fat line than in lean line females fed ad libitum or in restricted birds of both genotypes. 3. Mean cell haemoglobin concentration was higher and mean cell volume lower in fat compared with lean line females. 4. Food restriction was associated with lower plasma triglyceride concentrations, lower numbers of heterophils and monocytes and a lower heterophil-lymphocyte ratio. 5. Fat line birds had a higher blood pCO2 and lower pH than lean line birds. 6. Thermal stress was associated in ad libitum-fed birds with a rise in blood pH and a decrease in pCO2, and in restricted birds with a decline in blood pH and an increase in pCO2. 7. Blood creatine kinase activity increased in all groups under thermal stress.