Active immunization of broiler breeder cockerels against chicken inhibin accelerates puberty and prevents age-induced testicular involution

Injection of quail and breeder hens with a recombinant protein antigen (MBP-cINA521)--a fusion of the bacterical maltose-binding protein (MBP) and a fragment of the alpha-subunit of chicken inhibin (cINA521)--accelerates puberty and enhances lay. Herein, the effects of this immunogen on reproductive responses in broiler breeder males were assessed. Cockerels were subcutaneously injected with 0 (vehicular controls), 1, 3, or 5 mg of MBP-cINA521 at 13 wk of age and with one-half of these dosages (boosters) at 18 wk. Bird subsamples were weighed, blood sampled, and killed at 24, 28, and 39 wk of age to assess age and vaccination effects on BW, testes weight (TWT), TWT relative to BW (RTWT), TWT > or = 20 g (TWT20; theoretical threshold TWT for maximum fertility), and plasma testosterone. Breeder males are sexually developing, reach peak sexual activity, and show age-related reproductive decline at these ages. Because vaccine gonadal effects at 24 wk appeared to be dramatic, the size of the left testis was also scored to see if size differences could be detected by mere visual inspection. Male fighting increasingly reduced sample sizes beyond 24 wk. Because mortality was unrelated to the treatments and to insure meaningful statistical comparisons, MBP-cINA521 data were pooled. Body weight (P < 0.04), testis score (P < 0.02), TWT (P < 0.03), RTWT (P = 0.06), and plasma testosterone (P = 0.08) were elevated in immunogen-treated males at 24 wk of age, and more (P < 0.05) MBP-cINA521-treated birds than controls achieved a TWT20 at this time. These variables did not differ by treatment at 28 wk. However, by 39 wk, treatment effects reemerged as follows: TWT (P < 0.04), RTWT (P = 0.06), and TWT20 (P < 0.01) were increased in vaccinated males who also showed nearly 3-fold higher levels of plasma testosterone. We conclude that immunoneutralization of inhibin accelerates puberty and retards age-related sexual senescence that typically occurs in broiler breeder males.