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-de rived chicken prolactin. A second objective was to establish whether a ctive immunization against prolactin affects photoinduced onset of egg laying and the rate of egg production. The immunogen was a fusion pro tein (beta gal(s)-prolactin, 23 kDa) produced in Escherichia coli, com prising chicken prolactin (without the nine amino-terminal amino acids ) fused to 18 amino acids of E. coli beta-galactosidase. A control imm unogen was produced in the same strain of E. coli harbouring the same plasmid vector used to produce beta gal(s)-prolactin minus the prolact in gene sequence. Hens were immunized i.m. with 1 mg of protein contai ning 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 indu ced by increasing the daily photoperiod. The beta gal(s)-prolactin imm unogen, but not the control immunogen, stimulated the production of an tibodies to chicken prolactin. In Expts 1, 2 and 3, hens were placed i n floor pens with nest boxes after photostimulation to induce broodine ss. In these experiments, immunization with beta gal(s)-prolactin redu ced the incidence or delayed the development of broodiness. This effec t was more pronounced if immunization was initiated before, rather tha n after, the onset of egg laying. In Expts 1 and 2 hens were immunized with beta gal(s)-prolactin before photostimulation. The presence of a ntibodies to prolactin in their blood did not affect photoinduced onse t of egg laying. In Expt 4, hens were maintained in individual cages t o suppress the development of broodiness to measure the rate of egg la ying. In these conditions, hens immunized with beta gal(s)-prolactin l aid eggs at the same rate as did control hens. It is concluded that in the domestic hen increased prolactin secretion plays an important rol e in the initiation of incubation behaviour, and that active immunizat ion against prolactin does not affect photoinduced onset or subsequent rate of egg laying.