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Mechanisms mediating reproductive dysfunction in the hyperthermic laying hen (Gallus domesticus)
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The objective of the first experiment was to determine if thermal stress directly affects the endocrine regulation of ovulation. Hens were acutely heat stressed to limit the indirect effect of reduced feed consumption on the endocrine control of ovulation. Circulating levels of luteinizing hormone were characterized and hypothalamic/hypophyseal dysfunction elucidated. Additionally, the ability of the putative anti-stress compound, magnesium aspartate hydrochloride, to antagonize the effects of chronic heat stress in the hen was evaluated. In Experiment I, acute exposure to thermal stress (35C) lowered circulating levels of luteinizing hormone (LH) in the laying hen. Injection of LHRH in the hyperthermic hen resulted in a significantly greater release of LH at 30 and 60 minutes post injection when compared with normothermic hens injected with LHRH. Hypothalamic function was estimated in hens utilizing in-vitro techniques. One equivalent hypothalamic extract prepared from normothermic hens significantly increased LH release from dispersed pituitary cells. However, the same dose of hypothalamic extract from hyperthermic hens failed to evoke LH release from pituitary cells. Taken together, these data indicate hypothalamic dysfunction mediates the reproductive decline in the acutely heat stressed hen. In Experiment II, injection of magnesium aspartate hydrochloride (Mg-asp-HCL) reduced the body weight loss in hens exposed to 35C for 7 days. These hens demonstrated a consistent improvement in egg production. Mg-asp-HCL injection did not affect feed consumption, body temperature, or egg shell quality in normothermic or hyperthermic hens. In Experiment III, an immobilization stressor was employed to elucidate the mechanism of action of Mg-asp-HCL. Hens subjected to a 2 hour forced immobilization had a significant increase in circulating levels of corticosterone. Surprisingly, however, circulating concentrations of catecholamines were not affected in immobilized hens. Treatment of hens with Mg-asp-HCL did not affect corticosterone or catecholamine concentrations. In conclusion, exposure to acute thermal stress adversely affected the endocrine regulation of ovulation in the heat stressed hen. Additionally, the detrimental effects of both thermal stress and decreased feed consumption on hens during a chronic heat stress are reduced with Mg-asp-HCL treatment. The mechanism of action of Mg-asp-HCL is yet to be elucidated.
SubjectMajor poultry science
1987 Dissertation D687
Donoghue, Daniel James (1987). Mechanisms mediating reproductive dysfunction in the hyperthermic laying hen (Gallus domesticus). Texas A&M University. Texas A&M University. Libraries. Available electronically from
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