EFFECTS OF PASSIVE-IMMUNIZATION OF EWES AGAINST AN INHIBIN-PEPTIDE ONGONADOTROPIN-LEVELS, OVULATION RATE, AND PROLIFICACY

The experimental objectives were to determine whether injection of sem i-purified (sp; ammonium sulfate-precipitated) and highly purified (hp ; immunoaffinity-purified) ovine antibody (Ab) against an inhibin-pept ide fragment (alpha-IF) before the preovulatory period would 1) stimul ate FSH secretion in a dose-response manner, 2) induce an increase in ovulation rate, and 3) affect pregnancy rate and prolificacy (lambs bo rn alive per ewe lambing). During the early breeding season, estrus wa s synchronized in 30 2-yr-old crossbred ewes through use of progestero ne-releasing pessaries (CIDR-G). Two doses (330 and 660 laboratory ref erence preparation [RP-2] kU) of sp- and hp-alpha-IF-Ab were injected i.m. 48 h before CIDR-G removal (6 ewes per group). Six other ewes rec eived control solution. Plasma alpha-IF-Ab titers peaked at 12 h posti njection. Plasma FSH levels were higher (p < 0.02) in alpha-IF-Ab-trea ted ewes than in control ewes from 12 to 24 h postimmunization. Magnit udes of FSH increases were similar in ewes administered sp- and hp-alp ha-IF-Ab and were greater (p < 0.05) in ewes receiving 660 than in tho se receiving 330 RP-2 kU. Compared to control values, the higher alpha -IF-Ab dose increased FSH levels by 44 +/- 5% and the lower dose incre ased the levels by 22 +/- 3%. Plasma LH levels were similar among pass ively immunized and control sheep. Ovulation rate was increased (p < 0 .0005) by alpha-IF-Ab treatment. Higher ovulation rates were induced b y sp- than by hp-alpha-IF-Ab (3.1 +/- 0.1 vs. 2.7 +/- 0.2; p < 0.05) a nd by 660 than by 330 RP-2 kU (3.3 +/- 0.1 vs. 2.5 +/- 0.2; p < 0.01). Control ewes had an ovulation rate of 1.8 +/- 0.3. Positive associati ons existed between alpha-IF-Ab titers, FSH levels, and ovulation rate s. Number of lambs born per ewe lambing tended (p = 0.07) to be higher for alpha-IF-Ab-treated than for control ewes, but number of lambs bo rn alive was similar. In conclusion, passive immunization against alph a-IF prior to CIDR-G withdrawal stimulated FSH secretion and increased ovulation rate in a dose-related manner. Semi- and highly purified al pha-IF-Ab preparations were equally effective in stimulating FSH secre tion, while sp-alpha-IF-Ab was more effective than hp-alpha-IF-Ab in i ncreasing ovulation rate. Passive immunization against alpha-IF did no t affect pregnancy rate nor prolificacy.