Active immunization with vasoactive intestinal peptide in turkey hens

Active immunization of turkey hens against vasoactive intestinal peptide (V IP) has been shown to inhibit incubation behavior and to increase egg produ ction in second-cycle hens. The objective of this study was to compare the effect of VIP immunization on first- and second-cycle turkey hens during a 27-wk production period. First- (25-wk-old) and second- (54-wk-old) cycle h ens were intermixed, distributed among 16 pens, and subjected to a photoper iod of 6 h of light and 18 h of darkness for 10 wk. The first-cycle hens we re divided into two groups: keyhole limpet hemocyanin (KLH)-immunized contr ols (n = 16) and VIP-immunized (n = 18). Second-cycle hens were divided int o four groups: 1) unimmunized controls (n = 19), 2) KLH-immunized controls (n = 18), 3) VIP-immunized (n = 19), and 4) VIP-preimmunized (immunized dur ing first cycle; n = 16). Each hen received four antigen injections beginni ng the day of photostimulation (4-wk intervals), except for the preimmunize d hens, which received three injections beginning 4 wk after photostimulati on. The maximum titer of VIP antibodies in first-cycle, second-cycle, and p reimmunized hens was 17.2 +/- 2.2, 20.9 +/- 2.9, and 21.7 +/- 3.2%, respect ively. After photostimulation, plasma prolactin of first- and second-cycle control hens peaked between 484 +/- 105 and 630 +/- 118 ng/mL. In contrast, prolactin changed very Little in VIP-immunized turkeys. The average number of daily nest visits was less in first- and second-cycle VIP-immunized hen s (1.68 +/- 0.23 and 1.09 +/- 0.15 visits per hen per day, respectively) th an in their respective KLH-immunized controls (2.47 +/- 0.36 and 2.65 +/- 0 .45 visits per hen per day). Expression of incubation behavior was 50.0 and 52.6% in first- and second-cycle control hens, respectively, upon terminat ion of the study. In contrast, only 11.1% first-cycle and 5.2% second-cycle VIP-immunized turkeys exhibited the hormonal and behavioral characteristic s of incubating hens. Average weekly egg production of first- and second-cy cle VIP-immunized turkeys was similar (3.58 +/- 0.19 vs 3.63 +/- 0.14 eggs per hen per wk). First- and second-cycle control hens laid 2.63 +/- 0.25 an d 2.41 +/- 0.20 eggs per hen per wk, respectively. The present results show that comparable egg production was attained in first- and second-cycle hen s by active immunization with VIP.