Investigation of the primary cause of hypoadrenocorticism in South African angora goats (Capra aegagrus): a comparison with Boer goats (Capra hircus) and Merino sheep (Ovis aries).

Abstract

Our objective was to identify the primary site of the reduced adrenal function in South African Angora goats (Capra aegagrus) that causes a decrease in cortisol production and leads to severe losses of Angora goats during cold spells. Angora goats, Boer goats (Capra hircus), and Merino sheep (Ovis aries) were assigned to three intravenous treatments: 1) insulin, 2) corticotropin-releasing factor (CRF), and 3) ACTH. Blood cortisol concentrations were determined over a 90-min period to determine any differences in the response of the experimental animals to these treatments. For both the insulin and ACTH treatments, cortisol concentrations were less in Angora goats than in the other experimental animals. The adrenal gland was subsequently investigated as a possible cause for the observed hypoadrenocorticism. Primary adrenal cell cultures were prepared from these species, subjected to different treatments, and the cortisol production determined. Upon pregnenolone (PREG) addition, all the experimental animals' cortisol production increased significantly, with the production in Boer goats higher (P<.01) when compared with that in the other species. The stimulation of cortisol biosynthesis by ACTH was only obtained for Boer goats and Merino sheep. The stimulation of cortisol production by forskolin and cholera toxin were compared with ACTH, and, for Angora goats, only cholera toxin caused a significant increase in cortisol production. For Boer goats, no difference (P>.05) between the PREG, ACTH, forskolin, or cholera toxin treatments were observed. The Merino adrenal cells were increasingly stimulated in the following order: PREG, ACTH, forskolin, and cholera toxin (forskolin and cholera toxin stimulated cortisol production to the same extent). This investigation of the hypothalamic-pituitary-adrenocortical axis, therefore, identified the adrenal gland as the primary site of the Angora's hypoadrenocorticism.

Strategies for the genetic improvement of South African Angora goats

“…Angora goats were compared to Boer Goat and Merino sheep with regard to insulin-induced stress and ACTH and CRH stimulation, showing that plasma cortisol increased in both the Boer goat and Merino sheep while the absence of a response in the Angora indicated hypocortisolism (Engelbrecht et al, 2000). The potential cause was investigated by Storbeck et al, (2007Storbeck et al, ( , 2008Storbeck et al, ( , 2009) on a mitochondrial level who identified two cytochrome isoforms (CYP17) as the primary cause of hypocortisolism in the South African Angora goat.…”

Addisonian Crisis due to Metastatic Adenocarcinoma in a Pygmy Goat

“…Another experimental model successfully used both the low dose (0.4 IU/kg = 4 g/kg) and high dose (2.5 IU/kg = 25 g/kg) ACTH stimulation tests in Angora and Spanish wethers [7]. Physiologic resting cortisol concentrations have been reported to be between 1 and 15 ng/mL in healthy, adult goats [6][7][8], and a normal response was considered to be a minimum of 3-4-fold elevation of plasma cortisol after ACTH administration [6,7]. In dogs, a standard dose of synthetic ACTH (250 g/dog) is used for evaluation of adrenocortical function, regardless of the size of the dog, and a normal response is considered to be an 8-10-fold elevation in the cortisol concentration when compared to resting levels [9].…”

“…Primary hypoadrenocorticism has been previously reported in South African angora goats, resulting in increased sensitivity of these animals to weather changes [6], which appears to be genetic in this breed [7]. Diagnosis of Addison's syndrome is based on results of the ACTH stimulation test [3].…”

“…Diagnosis of Addison's syndrome is based on results of the ACTH stimulation test [3]. As this test is not routinely performed in goats, the ACTH dose used in this doe was selected based on a previous study, where it was successfully used to evaluate adrenal function in healthy Angora and Boer goats [6]. Another experimental model successfully used both the low dose (0.4 IU/kg = 4 g/kg) and high dose (2.5 IU/kg = 25 g/kg) ACTH stimulation tests in Angora and Spanish wethers [7].…”

“…Baseline cortisol concentrations were undetectable, and thus a follow-up ACTH stimulation test was performed using a dosage of synthetic ACTH of 10 g/kg. This dose was extrapolated from the results of a previous report [6]. Serum cortisol concentrations 1 hour after ACTH administration remained below detection range levels, and the diagnosis of adrenal insufficiency was made.…”