Effects of passive immunization using antibody against an alpha-inhibin peptide on follicle-stimulating hormone concentraions and litter size in sows

The objective of the experiment was to determine whether passive immunization against inhibin at weaning would increase FSH secretion and thereby influence postweaning reproductive performance in sows. Commercial Yorkshire sows (n = 173) were assigned within parity to 5 alpha-inhibin fragment antibody (alpha-IF-Ab) dosage groups: 0 (control), 3.25, 6.5, 13 and 26 RP-2 kU/kg alpha-IF-Ab. Antibody had been semipurified from ovine antisera raised against alpha-IF, a peptide that mimicked the N-terminal region of inhibin's alpha-subunit. A RP-2 U refers to a laboratory reference preparation. Sows were administered a single intramuscular injection of control solution or alpha-IF-Ab just before 21-d-old piglets were weaned. Blood samples were taken immediately before immunization and 24 h later. Sows were bred upon expression of estrus. Serum alpha-IF-Ab titers in sows 24 h following passive immunization increased (P0.001) with dosage. In control sows serum FSH concentrations decreased 24% by 24 h postweaning (P0.001). The decrease was diminished or prevented by alpha-IF-Ab treatment in a dose-responsive manner (P0.001). Most (167/173) sows were bred within 10 d postweaning, and wean-to-service intervals tended (P0.01) to be shorter in the 13 and 26 RP-2 kU/kg alpha-IF-Ab dosage groups. Farrowing rate was 72% (124/173) and was similar among sows in the alpha-IF-Ab dosage groups. Litter size, expressed as total or live piglets born per sow or per sow farrowed, was unchanged by alpha-IF-Ab treatment. Results demonstrate that (1) inhibin plays a key role in regulating FSH secretion at weaning, and (2) blocking the acute postweaning drop in FSH secretion has little if any effect on subsequent reproductive performance