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Title: THYMIC WEIGHT CHANGES AND ENDOCRINE RELATIONSHIPS DURING MATURATION IN CATTLE: EFFECTS OF AGE, SEX, AND CASTRATION

Author
item Wise, Thomas
item Klindt, John

Submitted to: Growth Development and Aging
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: The thymus gland makes chemicals called lymphokines, which affect growth, health, and reproduction. An understanding of how the thymus gland is regulated in its secretions could lead to improved domestic animal productivity. Studies were conducted to determine regulatory aspects of sex, age, and castration on the cow thymus. Thymic weights and secretory capacity decreased with age. Changes in thymic function were correlated with reproductive and pituitary hormonal changes. Such information indicates thymic function plays an important role in growth, health, and reproduction, and understanding regulation may improve animal productivity.

Technical Abstract: Elucidation of cause and effect relationships between gonadal and thymic function can be particularly challenging due to the complexity of interactions among various hormones on thymic function, many of which are largely unknown. To monitor gonadal-thymic interaction with the endocrine changes associated with maturity, bulls, steers, heifers, and ovariectomized heifers were slaughtered at 4, 6, 10, 12, or 14 months of age (n = 5-7/sex/age). Steers and ovariectomized heifers were castrated before 1 week of age. Thymic weights were increased in castrated animals as early as 4 weeks of age (p < 0.01), and differences were more pronounced in males. Thymic secretory peptide, thymosin beta-4, increased up to six months of age in all sex groups (p < 0.05) and then decreased with age, similar to the pattern of growth hormone. Prepuberal testosterone concentrations increased to 10-12 months of age and then decreased in both bulls and heifers, coordinate with decreases of thymosin beta-4 at 10 months of age. Relationships of LH were highly related to thymosin beta-4 changes in heifers during maturation. Changes of thymosin beta-4 and LH were coordinate in ovary-intact heifers and inversely related in ovariectomized heifers.