Hypocortisolism in Angora Goats

Tuesday, 20th March 2018

Text extracted from:  A REVIEW OF THE ROLE OF CYTOCHROME P450 17-HYDROXYLASE/17,20 LYASE (CYP17) IN HYPOCORTISOLISM IN SOUTH AFRICAN ANGORA GOATS 

  1. Storbeck1, M.A. Snyman2& P. Swart1#

Early investigations into cold stress related deaths in Angora goats implicated a dysfunction in the adrenal cortex as the probable cause.

Preliminary studies found that the primary cause of stock losses during cold spells was due to an energy deficiency resulting from a decrease in blood glucose levels, which causes a drop in body temperature and subnormal heart function (Wentzel et al., 1979).

Fourie (1984) subsequently demonstrated that Angora goats could not cope with cold, wet and windy conditions as well as the more hardy Boer goats, even when supplementary feeding practices were employed. Fourie (1984) concluded that the Angora goat does not have the metabolic capacity to produce sufficient heat. Cronje (1992) later demonstrated that Angora does have a lower blood glucose concentration and a slower response of glucose synthesis rate to dietary energy increments than Boer goat does, providing further evidence of the inability of the Angora goat to mobilise glucose precursors.

 IS THE ADRENAL CORTEX TO BLAME?

Following the study of Herselman & Van Loggerenberg (1995), which indicated that the South African Angora goat may suffer from a condition of hypocortisolism, the biochemistry laboratory at Stellenbosch University started investigating the Angora's adrenal steroidogenic pathway. 

THE ROLE OF CYP17

While pursuing CYP17 as the possible cause of hypocortisolism in the South African Angora goat, Slabbert (2003) identified two CYP17 isoforms in this species. 

Work by (Storbeck et al., 2008) goats were subsequently divided into three genotypes, namely: homozygotes for ACS- (Ho), heterozygotes yielding unequal peak areas (Hu) and heterozygotes yielding equal peak sizes (He) (Table 1).

Table: CYP17 genotyping. Goats were divided into three genotypes (Ho, Hu and He)

 

Ho

Hu

He

Angora goat Totals

16.49%

40.63%

42.88%

Boer goats

0%

0%

100%

 

 

  • The observation that all Boer goats, but not all Angoras genotyped to date are Hesuggests that this genotype originated in the Boer goat and not the Angora.
  • Although the origins of the Boer goat are vague, it is commonly accepted that this breed was developed by farmers in South Africa from indigenous African goats from as early as 1800, with the emergence of a distinct breed by the beginning of the 20th century (Casey & Van Niekerk, 1988).
  • The Angora goat was first imported into South Africa from Turkey in 1838. Many of the imported Angoras were crossed with the native goats during the early development of the mohair industry in South Africa. Some pure Angoras were, however, maintained for stud purposes (Hayes, 1882). The Boer goat fits the description of the native goats used in these breeding practices, albeit in the early stage of its development (Hayes, 1882). It is therefore suggested that it was these early breeding practices that led to the introduction of the second CYP17 gene (ACS+) into the South African Angora population.

 

IN VIVO STUDY

Subsequent to the identification of the three genotypes in the South African Angora goat population, the question arose whether the genotypes differed in their ability to cope with cold stress 

Plasma cortisol levels in the three Angora genotypes (n=10 per group) following intravenous insulin injection (Storbeck et al., 2007).

 

PRODUCTION DATA

This provides strong evidence that the CYP17 ACS- gene is responsible for the observed hypocortisolism in the South African Angora goat.

  • Genotyping for this gene may therefore be a useful tool for farmers to employ when selecting rams to breed with in order to reduce stock losses due to cold stress.
  • Statistical analysis revealed that there is no significant difference in the production data among the genotypes. Therefore, selection for more hardy goats based on the CYP17 genotype should not adversely affect the quality or quantity of mohair produced.
  • In addition to its importance in adrenal steroidogenesis, CYP17 is also vital to the production of sex steroids by the gonads (Payne & Hales, 2004). It is therefore possible that the differences in the activity of the CYP17 isoforms may affect the steroid output by the gonads. As these hormones play a critical role in determining the reproductive characteristics of the animal, the effect of the CYP17 genes on reproductive fitness will be investigated in a future study.   

 CONCLUSION

The results presented in this review have:

  • Clearly implicated CYP17 as the primary cause of hypocortisolism in the South African Angora goat.
  • A real-time PCR based genotyping method has been developed to distinguish between the three identified genotypes: Ho, Huand He. #
  • Goats from the Hegenotype have been shown to produce more cortisol in vivo, while still producing the same quantity and quality of mohair as the other genotypes.
  • The CYP17 gene is therefore a strong candidate to be used by farmers to aid in the selection of more hardy goats.

Also see BREEDING A HARDY ANGORA GOAT

 https://www.angoras.co.za/article/selecting-for-hardy-angora-goats#243

REFERENCES

TEXT EXTRACTED FROM:

A REVIEW OF THE ROLE OF CYTOCHROME P450 17-HYDROXYLASE/17,20 LYASE (CYP17) IN HYPOCORTISOLISM IN SOUTH AFRICAN ANGORA GOATS 

  1. Storbeck1, M.A. Snyman2& P. Swart1#

1Department of Biochemistry, University of Stellenbosch, Private Bag X1, Matieland, 7601

2Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900

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