Seasonal changes in the morphology and activity of wool follicles in Finewool and Strongwool Merino strains at different stocking rates in southern Australia
Date
1997
Authors
Hynd, P.
Hughes, A.
Earl, C.
Penno, N.
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Journal article
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Crop and Pasture Science, 1997; 48(7):1089-1097
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P. I. Hynd, A. Hughes, C. R. Earl and N. M. Penno
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Abstract
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An experiment was conducted to determine the impact of stocking rate and
Merino strain on follicle morphology before and after the break of the season
in the highly seasonal Mediterranean environment of southern Australia. Groups
of Finewool and Strongwool Merino sheep were allocated to 9 stocking rates on
mixed legume-grass pastures, and skin biopsy samples were taken at monthly
intervals from February to June. A scoring system, based on the morphology of
follicles in transverse section, was used to characterise these samples. The
proportion of follicles classified as ‘normal’ dropped markedly,
and the proportion of follicles which contained no fibre correspondingly
increased, after the break of the season in April. On average about 10%
of the follicles became inactive but there was considerable variability (range
2-63%) between animals.
The proportion of inactive follicles was significantly affected by stocking
rate but there was little difference between Merino strains. Maximum follicle
inactivity coincided with the period of minimum fibre diameter and minimum
liveweight in May, approximately 1 month after the break of the season. The
proportion of inactive follicles accounted for 27% and 28% of
the variance in staple strength of the Finewool and Strongwool strains,
respectively. Minimum fibre diameter accounted for 63% and 61%
of the variance in staple strength, and coecient of variation in fibre
diameter accounted for 49% and 58% of the staple strength
variance, respectively, in the 2 strains. Together, minimum fibre diameter and
coecient of variation in fibre diameter accounted for almost 75% of the
variance in staple strength in both strains. Addition of a term for the
proportion of inactive follicles did not remove any additional variance in
staple strength.
These results suggest that the follicles of Merino sheep in Mediterranean
environments undergo significant morphological changes throughout the year.
These changes differ from the normal sequence of events associated with the
hair cycle and appear to be associated with the break of the season in autumn.
The morphological changes which occur in the follicles are similar to those
induced by epidermal growth factor or cortisol, and may reflect a stress
response. Our results suggest that nutritional stress is at least partially
responsible for the follicular pathology described. Management strategies
aimed at reducing the decrease in fibre diameter which occurs in autumn,
shearing sheep in autumn to coincide with the minimum fibre diameter, and
selection of sheep which have a low coecient of variation of fibre diameter,
are likely to be the most effective means of preventing low staple strength in
sheep grazing in Mediterranean environments. Nevertheless, the impact of
follicle shutdown and changes in follicle morphology on wool characteristics
other than staple strength needs to be determined.
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© CSIRO 1997