EFFECTS OF PASSIVE-IMMUNIZATION USING ANTIBODY AGAINST AN ALPHA-INHIBIN PEPTIDE ON FOLLICLE-STIMULATING-HORMONE CONCENTRATIONS AND LITTER SIZE IN SOWS

The objective of the experiment was to determine whether passive immun ization against inhibin at weaning would increase FSH secretion and th ereby influence postweaning reproductive performance in sows. Commerci al Yorkshire sows (n = 173) were assigned within parity to 5 alpha-inh ibin 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 int ramuscular injection of control solution or alpha-IF-Ab just before 21 -d-old piglets were weaned. Blood samples were taken immediately befor e immunization and 24 h later. Sows were bred upon expression of estru s. Serum alpha-IF-Ab titers in sows 24 h following passive immunizatio n increased (P<0.001) with dosage. In control sows serum FSH concentra tions decreased 24% by 24 h postweaning (P<0.001). The decrease was di minished or prevented by alpha-IF-Ab treatment in a dose-responsive ma nner (P<0.001.). Most (167/173) sows were bred within 10 d postweaning , and wean-to-service intervals tended (P<0.1) 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 so w farrowed, was unchanged by alpha-IF-Ab treatment. Results demonstrat e that 1) inhibin plays a key role in regulating FSH secretion at wean ing, and 2) blocking the acute postweaning drop in FSH secretion has l ittle if any effect on subsequent reproductive performance. (C) 1998 b y Elsevier Science Inc.