Comparison of Hypothalamic Monoamine Contents of Broiler-and Layer- Type Chickens at Prehatch and Posthatch

Domestic chickens, which are precocial, have relatively well developed mechanisms of food intake regulation at hatch. Although their body weight is similar at hatch, broiler- and layer-type chickens have different growth rates and food intake following hatch. The purpose of the present study was to compare the hypothalamic content of the monoamines norepinephrine (NE), epinephrine (E), dopamine (DA) and serotonin (5-HT), and their metabolites dihydroxyphenylacetic acid (DOPAC), 4-hydroxy-3-methoxyphenylacetic acid (HVA) and 5-dihydroxyindolacetic acid (5-HIAA) between these strains on day 18 of incubation, and at 0 day-of-age. In both strains, 5-HT and 5-HIAA levels increased with age. On day 18 of incubation, the amounts of NE and E were almost the same between the two strains. Thereafter, the content of both monoamines rapidly increased at hatch in both strains, and layer-type chicken embryos had significantly higher E levels compared to broiler-type chicken embryos. The levels of DOPAC and HVA on day 18 of incubation were higher in broiler-type chicken embryos than in layer-type chicken embryos, but these differences were reduced at hatch. These changes at hatch may partly explain the difference in the performance between the two strains.