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The effects of active immunization against inhibin on production performance in female Japanese quail (Coturnix coturnix japonica) were assessed in two separate trials using an MBP-cINA521 fusion protein as an immunogen. The fusion protein, MBP-cINA521, consisted of the bacterial maltose binding protein (MBP) and a truncated form of the mature alpha-subunit of chicken inhibin (cINA521). MBP-cINA1521 was constructed by: 1) excising a 521-bp PstI fragment from a chicken inhibin alpha-subunit cDNA (cINA6; gift of P. A. Johnson), 2) cloning this fragment, which encodes all but the first 11 amino acid residues of the mature alpha-subunit, into the pMal-c2 vector of the MBP fusion expression system, and 3) expressing the fusion protein (MBP-cINA521) from the Escherichia coli and purifying it using affinity chromatography. In each trial, quail were randomly and equally assigned to one of two injection treatments as follows: 1) MBP-cINA521 in Freund's adjuvant, or 2) Freund's adjuvant (vehicular controls; CON). All immunizations were given subcutaneously and Freund's complete and incomplete adjuvant were used for primary and booster injections, respectively. In Trial 1, birds were given a primary challenge of 0.2 mg MBP-cINA521 per bird at 25 d of age, followed by booster immunizations (0.1 mg MBP-cINA521 per bird) at 33, 40, 47, 54 and 61 d of age and every 35 d thereafter. The CON birds received vehicular immunizations at the same time intervals. In Trial 2, birds treated with MBP-cINA521 received a primary challenge of 0.2 mg MBP-cINA521 per bird at 26 d of age, followed by booster immunizations (0.1 mg MBP-cINA521 per bird) using the same schedule as that used in Trial 1, with the exception that no boosters were given after 61 d of age. The CON birds received vehicular immunizations at the same time intervals. Collection of production performance data was initiated coincident with the laying of the first egg in each trial (i.e., beginning at 41 and 44 d of age for Trials 1 and 2, respectively) and continued for 30 1-wk periods of lay. Combined data from Trials 1 and 2 indicated that the mean +/- SE age at first egg lay was markedly decreased (P < 0.005) in MBP-cINA521-treated quail (53.4 +/- 0.9 d of age) when compared to the CON (57.6 +/- 1.3 d of age). Likewise, the mean +/- SE age at 50% egg production was reduced (P < 0.03) in quail immunized against inhibin (65.4 +/- 2.1 d of age) when compared to the CON (77.6 +/- 4.7 d of age). Total hen-day egg production was also higher (P < 0.05, Trial 1; P < 0.01, Trial 2) in MBP-cINA521-treated quail (88.7 +/- 1.4%, Trial 1; 90.1 +/- 1.2%, Trial 2) than in the CON birds (81.9 +/- 2.9%, Trial 1; 73.6 +/- 6.5%, Trial 2). Collectively, these findings provide evidence that inhibin immunoneutralization accelerated puberty and enhanced hen-day egg production during a 30-wk period of egg lay in Japanese quail.