Effects of immunization against α-inhibin using two adjuvants on daily sperm production and hormone concentrations in ram lambs

Twenty-five ram lambs were immunized against α-inhibin peptide emulsified in Freund's adjuvant (FRA), Emulsigen (EML) containing an oligodeoxynucleotide as an immunostimulant, or adjuvant without α-inhibin antigen (control). Four immunizations were administered during an 85-d period, after which testes were obtained for determination of daily sperm production (DSP) and histological evaluation. α-Inhibin antibody (Ab) titers were 70-fold greater in lambs treated with FRA than in EML-treated ram lambs. α-Inhibin immunization had no effect on testes weight or on plasma concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone. Mean DSP/g tended (P = 0.1) to be greater in α-inhibin–immunized (EML = 17.6 × 10⁶; FRA = 15.8 × 10⁶) ram lambs than in control animals (14.4 × 10⁶). One of the 8 control ram lambs had an elevated DSP/g, which was a statistical outlier. Without data from this lamb, DSP/g was increased (P < 0.01) in α-inhibin–immunized ram lambs by 28% over controls. No association was found between the titer of α-inhibin Ab developed and DSP/g. Histologically, the percentage of testicular area occupied by seminiferous tubules differed (P = 0.01) by treatment and was greatest (82%) in EML-treated ram α-inhibin–immunized lambs and lowest (74%) in control animals. Percentage tubular area and DSP/g were correlated (r = 0.57, P = 0.003). Findings show that (1) the extent of the increase in DSP/g is not dependent on the titer of α-inhibin Ab; (2) the increase in DSP/g is achieved through an increase in the mass of seminiferous tubules; and (3) FRA elicits a greater α-inhibin Ab titer than EML containing an oligodeoxynucleotide.