Immunization of heifers against gonadotropin-releasing hormone: antibody titers, ovarian function, body growth, and carcass characteristics
1995
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: .1 mg of HSA or .01, .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 < .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 +/- .1%). The numbers of heifers that became anestrous (plasma progesterone < .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 < .05) in GnRH-immunized (4.6 +/- .64, 4.0 +/- .70, and 3.6 +/- .60 for Treatments 2 to 4, respectively) compared with control heifers (9.4 +/- .20). During induced anestrus, follicular growth was generally arrested (< 5 mm in diameter) and plasma estradiol decreased. There was no effect (P > .10) of treatment on overall growth rate (ADG .54 +/- .041 and .51 +/- .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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