A study of ovine urinary 17 - hydroxycorticosteroid levels and their relation to changes in wool production : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science with Honours in the University of Canterbury [Lincoln College]

The most widespread fault which occurs in fleece wool produced in New Zealand is a condition known as ‘break’ or ‘tenderness’. Break is characterized by a marked decrease in the tensile strength of a part or parts of the staple. This is mainly the result if a decrease in fibre diameter. This fibre thinning can be attributed to conditions which cause a reduction in wool growth and is particularly prevalent in that portion of the fleece grown during the late winter – early spring period. The effect is most noticeable in wool from pregnant ewes. Although it occurs predominately at the time its occurrence is not restricted to pregnant ewes and break has been observed in all classes of sheep at various times of the year. While there is a seasonal reduction in wool production and in fibre diameter during the late winter – early spring period this in itself does not necessarily result in break. Although poor nutrition is considered to be a major cause of break there is abundant evidence to suggest that other factors which influence the wellbeing of the sheep are also involved. Many of these factors; disease, parasites, pregnancy management and climate, which are known to lead to fibre tenderness, are also known to cause hyperactivity of the adrenal cortex. Since Ferguson and his associates have shown that the adrenal cortex exerts a suppressive action on wool growth it has been proposed that temporary hyperactivity of the adrenal cortex, which results from these conditions, may be the under-lying physiological mechanism behind the occurrence of break, (Linder & Ferguson, 1956). The work to be described was carried out in an attempt to further elucidate the role of the adrenal cortex in wool production with particular reference to changes in fibre diameter. Since breed and individual differences is sensitivity to ‘break’ have been widely established, the breeds of sheep selected for this experiment were representatives of the highly efficient wool producing breeds, Merinos and Romneys and of the low efficiency breed, the Southdown. By exposing pregnant Southdown, Merino and Romney ewes to a low plane of nutrition per unit area could be depressed and a marked decrease in fibre diameter induced. These two parameters of wool production could then be related to changes in adreno-cortical activity, measured as urinary 17 – hydroxycorticosteroid (17-OHCS) excretion and the results compared with those obtained from non-pregnant sheep on an ad-libitum feed intake. During the preliminary stages of the trial it was necessary to investigate the methods available for the assessment of adreno-cortical function in sheep. Although the use of uniary 17-OHCS excretion as a measure of adreno-cortical function is a widely used technique in the field of clinical medicine, the difficulties associated with the application of such techniques to ovine urine have not been reported. A considerable portion of the thesis has been concerned with reviewing the methods available for the measurement of plasma and urinary corticosteroid levels in ruminant animals and the development of a method suitable for 17-OHCS determination in ovine urine