Immunization against inhibin enhances both embryo quantity and quality in Holstein heifers after superovulation and insemination with sex-sorted semen

The objective was to investigate the feasibility of improving embryo yield in superovulated cows following insemination with sex-sorted semen by prior immunization against inhibin. Twenty-eight heifers were allocated into three groups: High (n = 10), Low (n = 10), and Control (n = 8). The High group received one primary (1 mg) and two booster (0.5 mg) vaccinations (28-d intervals) with a recombinant inhibin α-subunit in 1 mL of white oil adjuvant, whereas the Low group received half that dose, and the Control group received only adjuvant. After the last immunization, all heifers underwent a standard superovulation treatment (decreasing doses of pFSH for 4 d), followed by two AI with 2 × 10⁶ sex-sorted semen after the onset of estrus. Inhibin-immunized heifers had higher (P < 0.01) plasma antibody titres, and an earlier onset of estrus (P < 0.05) than Control heifers. The total number of embryo/ova, transferable, and grade 1 embryos in the High group (15.4 ± 1.9, 5.7 ± 0.7, and 3.8 ± 1.0, respectively) was significantly greater than that of the Control group (9.1 ± 1.2, 3.1 ± 0.5, and 0.6 ± 0.2), but was intermediate (P > 0.05) in the Low group (13.0 ± 2.3, 4.4 ± 0.7, and 1.2 ± 0.3). There were no significant differences among groups in number of unfertilized ova and degenerated embryos. The High group also had higher (P > 0.05) plasma progesterone concentrations on the day of embryo collection. In conclusion, immunization against inhibin improved both embryo quantity and quality following superovulation and insemination with sex-sorted semen.