Active Immunization of Prepubertal Colts Against Estrogens: Hormonal and Testicular Responses After Puberty

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Abstract
Prepubertal Quarterhorse colts were immunized at 6 mo of age with either estrone-17-oxime-bovine serum albumin (n=4; treated) or with albumin only (n=5; controls). All colts received booster injections of the appropriate antigen at 8, 10, 12, 16 and 20 mo of age. Blood samples were drawn every 20 d from 6 to 26 mo of age; body weights were determined monthly. Immunization against estrone-albumin resulted in increased binding of [3H]-estradiol in serum within 40 d that was maintained through 24 mo of age. Antisera from treated colts crossreacted equally well with estrone and estradiol and moderately with other estrogens; androgens, progesterone and glucocorticoids all cross-reacted <.005%. Body weights were not affected by treatment. Concentrations of testosterone were generally higher (P<.05) in estrogen-immunized colts compared with controls after immunization. Concentrations of luteinizing hormone were not affected by treatment, whereas concentrations of follicle-stimulating hormone were initially increased (P<.05) in treated colts after immunization. At castration at 27 mo of age, estrogen-immunized colts had greater (P<.05) testicular and parenchymal weights and produced more (P≅.055) spermatozoa per horse than did control colts. Seminal characteristics immediately before castration were not affected by treatment. It appears that estrogens are involved in the regulation of several reproductive traits in the colt. Moreover, active immunization against estrogen in the prepubertal colt may be a useful method of increasing testicular size and sperm production rates in the stallion after puberty. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.