Effects of single or primary plus booster prostaglandin F2 alpha immunization regimens on immune, ovarian, and growth responses of heifers.

Growth rate of heifers is reduced by prostaglandin F2 alpha (PGF) immunization following a primary and booster regimen. The objective was to attenuate the immune response with or without a booster immunization; specifically, the effects of booster interval, dose of PGF-human serum albumin (HSA) conjugate at booster, adjuvant type, or single immunization with one or two adjuvants were examined. Three experiments were conducted using 175 cyclic heifers. Plasma PGF antibody titers were measured every 2 wk and progesterone concentrations every 3 to 4 d. In Exp. 1, single immunization with one adjuvant (3.3 mg of PGF-HSA in either DEAE-dextran [DEAE] or non-ulcerative Freund's adjuvant [NUFA]; or 10.0 mg of PGF-HSA in NUFA) did not induce sufficient antibody titers to consistently induce persistent corpora lutea (CL). Booster intervals of either 14, 21, or 28 d increased titers sufficiently to induce persistent CL (34/35 heifers), but ADG of heifers was less (P < .05) than for those given a single immunization. In Exp. 2, 1.0 mg of conjugate for booster immunization induced a greater (P < .05) immune response than 3.3 mg, and both doses decreased (P < .05) ADG. Single immunization, with half the conjugate dose in DEAE and half in NUFA injected separately, induced persistent CL in 7/8 heifers without decreasing ADG compared with controls. In Exp. 3, single immunization, with half the conjugate dose in DEAE and half in NUFA injected separately, prolonged (P < .05) the intervals to peak titer compared with the booster treatment, but the incidence (13/15 vs 8/8) and duration (120 +/- 4.8 vs 111 +/- 7.9 d) of persistent CL were similar, and ADG was greater (P < .05). In conclusion, attempts to attenuate the immune response following booster immunization were unsuccessful. Single immunization, using two adjuvants separately, induced persistent CL for at least 120 d without decreasing ADG compared with the primary and booster regimen.