Effects of active immunization with inhibin alpha subunit on reproductive characteristics of turkey hens

The hypothesis for the present study is that the active immunization of fem ale turkeys with inhibin (INH) would neutralize endogenous INH, and increas e levels of circulating follicle stimulating hormone (FSH) and the number o f preovulatory follicles, and subsequently enhance egg production. Two expe riments were conducted with female turkeys in their first (30 wk of age) an d second (62 wk of age) laying cycles. Treatment groups included control tu rkeys immunized with keyhole limpet hemocyanine (KLH) and experimental turk eys immunized with recombinant turkey inhibin alpha conjugated to KLH (rtIN H), vasoactive intestinal peptide (VIP) conjugated to KLH or rtINH+VIP. Egg production increased (P < 0.05) in VIP and rtINH+VIP immunized birds, but not in rtINH immunized hens in comparison with a control group. A similar n umber of ovarian follicles, arranged in the follicular hierarchy of laying hens, was observed in all experimental groups. However, there was a larger number of nongraded yellow follicles in rtINH-immunized (62.5%) and rtINH+V IP-immunized (73.5%) groups compared with that of controls, suggesting over stimulation by FSH. Anterior pituitary FSH beta subunit, LH beta subunit, a nd prolactin (PRL) mRNA contents were determined by Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) in laying hens at the end of the experimental period. Hens immunized with rtINH showed in creased FSH beta subunit mRNA content, but no change in the content of LH b eta subunit or PRL mRNA. Hens immunized with VIP or rtINH+VIP had significa nt increases in both pituitary LH beta subunit and FSH beta subunit mRNA co ntents, accompanied by a decline in PRL mRNA abundance. The magnitude of th e increase in FSH beta subunit to INH immunoneutralization was greater in f irst-cycle hens than in second-cycle hens. These data suggest that active i mmunization of female turkeys with INH neutralizes endogenous INH and incre ases both circulating FSH and the number of preovulatory follicles. However , no significant increase in egg production was observed in INH-immunized h ens. The data confirm previous reports that VIP immunoneutralization increa ses egg production in turkey ens an shows for the first time that it also i ncreases FSH beta subunit and LH beta subunit gene expression.