Immunization of heifers against gonadotropin-releasing hormone: antibody titers, ovarian function, body growth, and carcass characteristics.
Prendiville D.J. | Enright W.J. | Crowe M.A. | Finnerty M. | Hynes N. | Roche J.F.
To investigate the effects of active immunization of cyclic beef heifers with different doses of a human serum albumin-Cys-Gly-GnRH ( HSA-GnRH) conjugate on antibody titers, ovarian function, body growth, and carcass characteristics, 32 heifers (BW = 477 +/- 7.1 kg; mean +/-SE) were assigned to one of four immunization treatments: 0.1 mg of HSA or 0.01, 0.1, or 1.0 mg of HSA-GnRH, respectively All heifers received a primary (d 0) and booster (d 28) immunization using DEAE-dextran as adjuvant. The duration of the experiment was 158 d. Overall antibody titers against GnRH were greater (P < 0.05) for heifers immunized against GnRH (13 +/- 3.3, 22 +/- 3.8, and 19 +/- 2.8% binding at a plasma dilution of 1: 640 for Treatments 2 to 4, respectively) than for controls (1 +/- 0.1%). The numbers of heifers that became anestrous (plasma progesterone < 0.5 ng/mL for > 21 d) were 1/8, 8/8, 7/8, and 8/8, respectively. The interval from primary immunization to anestrus 40.7 +/- 6 d) and the duration of anestrus (78 +/- 7 d) were not affected by dose of HSA-GnRH conjugate. The number of ovulations detected was reduced ( P < 0.05) in GnRH-immunized (4.6 +/- 0.64, 4.0 +/- 0.70, and 3.6 +/- 0.60 for Treatments 2 to 4, respectively) compared with control heifers (9.4 +/- 0.20). During induced anestrus, follicular growth was generally arrested ( < 5 mm in diameter) and plasma estradiol decreased. There was no effect ( P > 0.10) of treatment on overall growth rate (ADG 0.54 +/- 0.041 and 0.51 +/- 0.054 kg for control and GnRH-immunized heifers, respectively) or carcass measurements. However, ADG was reduced for GnRH-immunized heifers between d 56 and 84. In summary, immunization of heifers with a HSA-GnRH conjugate invoked an immune response in all heifers and induced anestrus in 23/24 heifers for 82.8 +/- 6.9 d; dose of HSA-GnRH conjugate did not affect the incidence or duration of anestrus.
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