Adrenocortical response to ACTH in Angora and Spanish goat wethers
C. A. Toerien, R. Puchala, J. P. McCann, T. Sahlu, and A. L. GoetschJournal of Animal Science 77:1558-1564. 1999.
Angora goats, on a body weight basis, are the highest fleece-producing ruminant, but are susceptible to stress. rrespective of sex, Angora goats exhibit an apparent impaired capacity for gluconeogenesis and a consequent inability to raise blood glucose levels under cold and(or) nutritional stresses. This may contribute to abortions and adult fatalities. It has been hypothesized that the decreased gluconeogenic ability of Angora goats is simply due to nutrient partitioning to fiber production at the expense of labile body protein reserves and glucogenic precursors. However, subclinical hypoadrenocorticism could exist in Angora goats as well. Likewise, it has been postulated that genetic selection for mohair production has been accompanied by coselection for hypoadrenocorticism, since cortisol inhibits fiber follicle activity. In primary hypoadrenocorticism, low cortisol production and blood levels result from low adrenal cortisol release in response to adrenocorticotropin hormone (ACTH) stimulation, because of factors such as low adrenal mass and atrophy or destruction of the adrenal cortices; secondary hypoadrenocorticism is the product of low pituitary ACTH production. Integrity of the adrenal cortex of Angora goats has not been directly studied. Thus, in this study the hypothesis that Angora goats exhibit subclinical primary hypoadrenocorticism was tested by measuring plasma cortisol response in stress-tolerant Spanish and stress-intolerant Angora goats under conditions of simulated acute and chronic ACTH challenges. Based on results of this experiment, the adrenal cortex in Angora goat wethers appears fully capable of mounting an appropriate cortisol response to adrenocorticotropic hormone stimulation. Thus, the ability of Angora goats to cope with stress may involve factors other than the capacity of the adrenal cortex to produce cortisol. However, possible changes in hypothalamic-pituitary-adrenal cortex axis function due to pregnancy and(or) dysfunction in cell-signaling mechanisms for cortisol action may play a role in the well established stress intolerance of Angora goats.
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