Studies on prolactin in galliformes

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A problem of considerable economic importance to the poultry producer is the occurrence of incubation behavior ("broodiness") in breeder hens. This behavior is characterized by increased nesting frequency, incubation of eggs, involution of the ovary, anorexia, adipsea and large changes in intermediary metabolism. As a result of the expression of this trait, substantial costs are incurred due to both the loss of egg production and to the more intensive labour/management procedures that are required for prevention. The pituitary hormone, prolactin (PRL) is thought to play a key role in broodiness since blood levels increase 6 to 10 fold at the onset and are maintained at high levels throughout the expression of the behavior. Among vertebrate species, greater than 300 biological actions of PRL have been described but how PRL is involved in the physio-behavioural repertoire associated incubation is unknown. We have recently noted that up to 8 different post-translationally modified forms of PRL (glycosylation, phosphorylation) are secreted by the pituitary and the ratio of these forms varies greatly during the life cycle of chickens and turkeys. Notably, the modified forms are dominant (>75 %) during incubation behavior and during the late stages of embryogenesis. This is an unexpected result since mammalian PRLs generally have reduced binding affinity to the receptor and are more rapidly cleared from the blood. The avian PRL receptor may be activated in specific tissues differently at specific stages of the life cycle by these altered PRLs. In order to study, the effects of PRL we plan 1) to knock down expression of PRL using RNA interference 2) to purify the various isoforms and test receptor activation 3) to continue genetic analysis of this and other candidate genes which can be used for marker assisted selection to reduce broodiness in breeder hens.