Active immunization of turkey hens against vasoactive intestinal peptide (VIP) has been shown to inhibit incubation behavior and to increase egg production 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 hens were intermixed, distributed among 16 pens, and subjected to a photoperiod of 6 h of light and 18 h of darkness for 10 wk. The first-cycle hens were divided into two groups: keyhole limpet hemocyanin (KLH)-immunized controls (n = 16) and VIP-immunized (n = 18). Second-cycle hens were divided into four groups: 1) unimmunized controls (n = 19), 2) KLH-immunized controls (n = 18), 3) VIP-immunized (n = 19), and 4) VIP-preimmunized (immunized during first cycle; n = 16). Each hen received four antigen injections beginning the day of photostimulation (4-wk intervals), except for the preimmunized hens, which received three injections beginning 4 wk after photostimulation. The maximum titer of VIP antibodies in first-cycle, second-cycle, and preimmunized hens was 17.2 ± 2.2, 20.9 ± 2.9, and 21.7 ± 3.2%, respectively. 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 hens (1.68 + 0.23 and 1.09 ± 0.15 visits per hen per day, respectively) than 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 termination of the study. In contrast, only 11.1% first-cycle and 5.2% second-cycle VIP-immunized turkeys exhibited the hormonal and behavioral characteristics of incubating hens. Average weekly egg production of first- and second-cycle 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 and 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 hens by active immunization with VIP.
- Incubation behavior
- Vasoactive intestinal peptide