Effect of active immunization of cattle against inhibin on ovarian follicular development and ultrasound-guided transvaginal follicular aspiration

Abstract

The effects of active immunization of cattle against inhibin on ovarian follicular development and ultrasound-guided transvaginal follicular aspiration were determined. Six Multiparous Japanese Black were actively immunized with a synthetic peptide replica of the amino acid sequence from 1 to 26 (numbering from the N-terminal end) position of the α-subunit of porcine inhibin (pINH) conjugated with rabbit serum albumin (RSA) using Freund's complete adjuvant. At 6, 10 and 14 wk after the primary injection, booster injections of the peptide were given. As controls, 6 Japanese Black received rabbit serum albumin as described above. Blood samples were taken at 0, 2, 6 wk and once a week from 10 to 17 wk after the primary injection to measure antibody titer. The changes in the numbers of recruited follicles of the 3 size categories (small, 2 to 3 mm; medium, 4 to 9 mm and large, ≥ 10 mm) and aspirated oocytes were examined once a week from 10 to 17 wk using ultrasound scanning. Antibody titers increased after the first booster in all immunized cattle. In comparison with controls, inhibin-immunized cattle had more small, medium and large follicles during the ultrasound scanning (16.0 ± 1.8, 4.0 ± 0.6 and 2.2 ± 0.3 versus 9.1 ± 0.5, 1.7 ± 0.2 and 1.1 ± 0.1, respectively; P < 0.05). In addition, the number of oocytes collected by transvaginal follicular aspiration was significantly greater (P < 0.05) in the inhibinimmunized cattle (10.4 ± 1.7) than in the controls (4.2 ± 0.5). These results demonstrate that in cattle active immunization against inhibin can enhance ovarian follicular development and the number of oocytes collected by transvaginal follicular aspiration.