Effects of Social Conditions on Sexual Behavior, Luteinizing Hormone Concentrations, and Testosterone Concentrations in Yearling Beef Bulls PDF Download

Author: Roger Dwayne Smith
Publisher:
ISBN:
Category : Beef cattle
Languages : en
Pages : 182

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Author: Paul Edward Juniewicz
Publisher:
ISBN:
Category :
Languages : en
Pages : 146

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Author: Theodore D. Kemper
Publisher: Rutgers University Press
ISBN: 9780813515519
Category : Psychology
Languages : en
Pages : 286

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Explorations in the Socio-Bio-Social Chain

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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 420

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"Education, arts and social sciences, natural and technical sciences in the United States and Canada".

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Category :
Languages : en
Pages :

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A series of experiments was conducted to evaluate the effects of nutrition during calfhood (defined as the period from 10 to 26-30 wk of age) and peripubertal period (defined as the period from 27-31 to 70-74 wk of age) on sexual development and reproductive function in beef bulls. The overall objective of these experiments was to evaluate the effects of nutrition on endogenous metabolic hormones (leptin, insulin, GH, and IGF-I), gonadotropins and testosterone concentrations, sexual development, sperm production, and semen quality in bulls. The results of these experiments demonstrated that nutrition affected GnRH secretion and sexual development in bulls. Increased nutrition during calfhood resulted in a more sustained increase in LH pulse frequency during the early gonadotropin rise and greater testicular development at maturity. On the other hand, low nutrition during calfhood suppressed LH secretion during the early gonadotropin rise and resulted in delayed puberty and reduced testicular development at maturity. When low nutrition was accomplished by restricted feed intake, hypothalamic and pituitary function were compromised and LH secretion was more severely affected. Temporal associations between LH secretion patterns and circulating IGF-I concentrations implied that IGF-I is a possible signal to the central metabolic sensor involved in translating body nutritional status to the GnRH pulse generator. Nutrition also affected testicular steroidogenesis (testosterone concentrations), indicating effects on the number or function of Leydig cells, or both. Age-related increases in physiological and GnRH-stimulated circulating testosterone concentrations were hastened in bulls receiving high nutrition and delayed in bulls receiving low nutrition; these effects were probably mediated by both LH secretion and IGF-I concentrations. Circulating leptin and insulin may have only permissive roles on GnRH secretion, but may enhance testicular development. Growth hormone con.

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Category : Agricultural experiment stations
Languages : en
Pages : 38

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Author: Kentucky Agricultural Experiment Station
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Category : Agricultural experiment stations
Languages : en
Pages : 254

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Author: Robert Wayne Godfrey
Publisher:
ISBN:
Category : Beef cattle
Languages : en
Pages : 392

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Author: Sherry M. Lane
Publisher:
ISBN:
Category : Beef cattle
Languages : en
Pages : 102

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Author: Di Wu
Publisher:
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Category :
Languages : en
Pages : 362

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Age-related declines of androgens and libido in males have been observed for decades. This dissertation sought to elucidate the mechanisms by which hormones may act differentially upon their receptors in the hypothalamus of aging compared to young males. I also examined how sexual experience modulates the ability of hormones to facilitate sexual behavior with aging. Experiment one measured androgen receptors (AR) and estrogen receptor [alpha] (ER[alpha]) cells in male rats at young, middle-aged and old age. I found that AR cell numbers in hypothalamic regions studied underwent significant age-related increases. Numbers of heavily ER[alpha] labeled cells, but not total ER[alpha] cells, increased with age. This study demonstrates that the aging brain has the capacity to synthesize hormone receptors which is increased possibly due to decreased testosterone concentrations. Experiment two examined the effect of sexual experience on serum hormones and cells of AR and ER[alpha] in hypothalamic regions in young and middle-aged males. The results showed that AR cell numbers increased with aging but did not change with experience. No age- or experience-related alteration in ER[alpha] expression occurred. However, serum testosterone increased and estradiol decreased with age. Experience increased total and free testosterone. Interactions of age and experience on total testosterone, estradiol, and luteinizing hormone were found. These results show long-lasting effects of sexual experience on hormones, but not on their receptors in the hypothalamus. Experiment three investigated effects of exogenous testosterone on sexual behavior in young and middle-aged males. The results showed a decline in sexual behavior parameters with age. After castration with testosterone treatment, there were few differences in sexual behavior measures between young and middle-aged males. AR cell numbers were higher and ER[alpha] cell numbers lower in testosterone compared to vehicle-treated males of both ages, and few effects of age occurred. These findings indicate that testosterone and aging interact in a complex manner to control numbers of cells expressing hormone receptors in the brain and on the subsequent control of sexual behavior. This insight provides a better understanding of the relationship between molecular changes in the brain and behavior, and suggests new therapeutic targets to human testosterone treatment.