Effect of active immunization against recombinant-derived chicken prolactin fusion protein on the onset of broodiness and photoinduced egg laying in bantam hens.

The hypothesis that the onset of incubation behaviour (broodiness) in the domestic hen is induced by an increase in prolactin secretion was investigated by actively immunizing bantam hens against recombinant-derived chicken prolactin. A second objective was to establish whether active immunization against prolactin affects photoinduced onset of egg laying and the rate of egg production. The immunogen was a fusion protein (beta gals-prolactin, 23 kDa) produced in Escherichia coli, comprising chicken prolactin (without the nine amino-terminal amino acids) fused to 18 amino acids of E. coli beta-galactosidase. A control immunogen was produced in the same strain of E. coli harbouring the same plasmid vector used to produce beta gals-prolactin minus the prolactin gene sequence. Hens were immunized i.m. with 1 mg of protein containing 0.8-0.9 mg of fusion protein in Freund's incomplete adjuvant at 4-8 week intervals beginning before or after egg laying, which was induced by increasing the daily photoperiod. The beta gals-prolactin immunogen, but not the control immunogen, stimulated the production of antibodies to chicken prolactin. In Expts 1, 2 and 3, hens were placed in floor pens with nest boxes after photostimulation to induce broodiness. In these experiments, immunization with beta gals-prolactin reduced the incidence or delayed the development of broodiness. This effect was more pronounced if immunization was initiated before, rather than after, the onset of egg laying. In Expts 1 and 2 hens were immunized with beta gals-prolactin before photostimulation. The presence of antibodies to prolactin in their blood did not affect photoinduced onset of egg laying.(ABSTRACT TRUNCATED AT 250 WORDS)