PASSIVE-IMMUNIZATION OF EWES AGAINST AN INHIBIN-LIKE PEPTIDE INCREASES FOLLICLE-STIMULATING-HORMONE CONCENTRATIONS, OVULATION RATE, AND PROLIFICACY IN SPRING-MATED EWES

The objective of this experiment was to determine whether passive immu nization against a synthetic inhibin-like peptide (alpha-IF) increases FSH secretion and reproductive performance of ewes bred in the spring . Crossbred ewes were assigned to three treatment groups of 10 ewes ea ch. Progesterone-releasing pessaries (CIDR-G) were inserted and left i n place for 12 d. The CIDR-G were removed on April 7 (0 h), and three rams were introduced. A single 1.8-mL i.m. injection containing 0, 315 -, or 630-reference preparation-2 (RP-2) kU semipurified alpha-IF-anti body (Ab) was given at -48 h. Antibody solution was prepared by ammoni um sulfate precipitation and concentration of ovine immune sera that h ad been generated against alpha-IF-human-alpha-globulin. After the alp ha-IF-Ab injection, plasma alpha-IF-Ab titers and FSH concentrations i ncreased within 6 h, peaked 12 to 24 h later, and then decreased. At 1 2 h after injection, FSH concentrations were increased (P = .05) 28 an d 42% over control values in ewes injected with 315- and 630-RP-2 kU a lpha-IF-Ab, respectively. All ewes expressed estrus and ovulated, exce pt one control that did not ovulate. Ovulation rate (OR) was increased (P < .0001) by alpha-IF-Ab treatment. Mean OR was 1.0 in control ewes , 1.7 in ewes given 315-RP-2 kU, and 2.5 in ewes injected with 630-RP- 2 kU. Fertility (ewes lambing/ewes exposed) from breeding at the induc ed-synchronized estrus tended (P = .09) to be greater for ewes injecte d with 630-RP-2 kU alpha-IF-Ab. Number of lambs born/ewe lambing and p rolificacy (number of lambs born alive/ewe lambing) were increased (P < .02) by alpha-IF-Ab-treatment. Respective number of ewes lambing, la mbs born/ewe lambing, and lambs born alive/ewe lambing were as follows : control = 7, 1.0, .7; 315-RP-2 kU = 6, 1.7, 1.7; 630-RP-2 kU = 10, 1 .8, 1.6. In conclusion, passive immunization of ewes against or-IF dur ing spring 1) increased FSH secretion, 2) increased OR in a dose-relat ed manner, and 3) increased prolificacy.