Stimulus requirements for prolactin and LH secretion in incubating ring doves

To study the regulation of prolactin secretion and incubation behavior during breeding, stimuli available during the prehatching period were manipulated, and plasma prolactin and LH and pituitary prolactin concentrations were assayed. Four groups were compared: (a) nest and eggs removed (b) eggs replaced with infertile eggs, (c) eggs replaced with infertile eggs and partners separated, and (d) unmanipulated controls. The increase in prolactin secretion that normally occurs at the end of incubation was reversed when the nest and eggs were removed but was unaffected by the absence of the mate. Prolactin secretion was not maintained in males sitting beyond the normal incubation period (on infertile eggs), while it was maintained in females but only in the presence of the mate. In the control birds, the increase in plasma prolactin was accompanied by an increase in pituitary content; while in the manipulated groups, an inhibition of prolactin secretion was associated with a transient increase in pituitary content. Plasma LH levels were low in control birds during the time of high prolactin secretion, and in all groups where the disruption of normal breeding stimuli caused an early fall in prolactin, there was a concomitant increase in LH secretion. In animals which had been separated from their mates and provided with a nest bowl and eggs, continuous observations of incubation behavior were made and plasma was sampled every third day. Parallel changes in prolactin and sitting behavior occurred in some of the animals, while others continued to incubate after prolactin had declined. In no instance did an animal which maintained high prolactin show a decline in incubation. This suggests that prolactin can serve to maintain incubation, while incubation does not necessarily stimulate prolactin secretion at this phase of the breeding cycle.