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Circulating levels of corticosterone were determined in chick embryos from 10 to 21 days of incubation using eggs from a Leghorn breeder flock. In Experiment 1, eggs were incubated from 10 to 20 days for daily embryonic blood collection. To verify stage of development with day of incubation, embryo right middle toe lengths were measured concurrent with blood sampling. Serum from three embryos was pooled into one sample and the corticosterone content of 10 samples per day of incubation was determined using a radioimmunoassay procedure. The levels of corticosterone from day 10 to 14 fluctuated slightly and then increased rapidly until 16 days of incubation. At this time serum corticosterone remained relatively constant through day 18 with an apparent increasing trend up to day 20. The use of toe lengths to assure no day-to-day overlap in embryonic development proved effective. In Experiment 2, newly hatched (day 21) chicks were sorted into four 3-hr periods ranging from early to late hatching. Blood samples were collected from five individual chicks during four 15-min sampling periods for each of the four hatch times. Serum corticosterone levels were not affected by sampling periods or hatch times.

The effect of lipopolysaccharide (LPS) on the expression of proinflammatory cytokines, interleukin (IL)-1beta, IL-6, and IL-12 in broiler chick thrombocytes was investigated. At 4 wk of age, blood samples were collected, and isolated thrombocytes were incubated with LPS for 1 h. Ribonucleic acid was extracted from the cells to examine the expression of the proinflammatory cytokines using real-time reverse transcription PCR. It was found that expressions of IL-1beta, IL-6, and IL-12 in thrombocytes were unaffected by diets containing corticosterone and vitamin C fed to chicks. However, LPS exposure did increase the expressions of these cytokines. The fact that thrombocytes are so abundant and can be stimulated by LPS makes them primary effector cells in innate host defenses against bacterial infections in chickens.