Effects of Immunization of Heifers against Estradiol on Growth, Reproductive Traits, and Carcass Characteristics

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Abstract
An experiment was performed to evaluate the effects of active immunization of heifers against estradiol on feedlot performance (growth and efficiency), carcass characteristics, and reproductive functions. Crossbred heifers (72) were divided into 4 equal treatment groups consisting of controls, ovariectomized heifers, and heifers actively immunized against keyhole limpet-estradiol antigen and bovine serum albumin-estradiol antigen. Heifers were fed ad lib for 170 days. Both groups of heifers immunized against estradiol had higher (P < 0.05) average daily gains than controls. Heifers immunized against bovine serum albumin-estradiol had increased feed efficiency (P < 0.05) over controls. Ovariectomized heifers did not perform at levels sufficient to compensate for the initial setback from surgery. No differences were noted in carcass grade, quality, or concentration of water, fat or proteins. Uterine weights were increased in estrogen-immunized animals but were not significantly greater than controls. Ovarian weights and numbers of large follicles (> 9 mm diameter) in immunized animals were significantly greater than in controls. Of the animals (n = 5) in the bovine serum albumin-estradiol-immunized group, 28% had cystic follicles (> 20 mm diameter) and 50% (n = 9) of this group had no detectable corpus luteum. Low titer (1:100) systemic binding of estrogens may act as a steroid reservoir in which systemic estrogen clearance is decreased and availability to target tissues is increased.