Variations in concentrations of prolactin, luteinizing hormone, growth hormone and progesterone in the plasma of broody bantams (Gallus domesticus).

The concentrations of prolactin, LH, progesterone and GH were measured in the blood of broody bantam hens. The concentration of prolactin was at its highest when the birds began to incubate their eggs and in six out of nine hens it tended to remain raised until the eggs hatched. The increase in the concentration of prolactin was small: in incubating hens it was only 23% higher than in hens caring for their young and 14% higher than in laying hens (P less than 0.05 for both comparisons). The concentration of GH tended to be depressed in hens caring for young but otherwise was not related to reproductive activity. The concentrations of LH and progesterone decreased at the onset of incubation and remained depressed while the hens sat on their eggs (P less than 0.001) for both comparisons). After the chicks hatched, the level of LH began to increase slowly whereas the level of progesterone remained low. The hens stopped showing broody behaviour between 4 and 10 weeks after the chicks had hatched; this corresponded to the time when the concentration of LH had increased to values found in laying hens. These observations provide some evidence that prolactin secretion increases at the onset of incubation and support the view that the hormone is not secreted at an increased rate while hens are caring for their young.