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Plant sciences, sustainable farming systems and food quality
RESEARCH ARTICLE

Development of black pigmented skin spots and pigmented wool fibres in a Merino flock—causes, field observations, and wool measurement

M. R. Fleet
+ Author Affiliations
- Author Affiliations

South Australian Research and Development Institute, Livestock Systems Alliance, Turretfield Research Centre, Rosedale, SA 5350, Australia. Email: fleet.malcolm@saugov.sa.gov.au

Australian Journal of Agricultural Research 57(7) 751-760 https://doi.org/10.1071/AR05032
Submitted: 31 January 2005  Accepted: 1 February 2006   Published: 14 July 2006

Abstract

The development of black-grey pigmented skin spots and pigmented wool fibres on adult Merino sheep over a 3-year period was assessed. Effects of long-term grazing of oestrogenic pasture and multiple shearing were studied. The number of affected sheep and number of pigmented spots on affected sheep increased with age, with the greatest increase at 8.5 years age. Grazing of oestrogenic pastures had no effect but twice yearly shearing increased the development of pigmented spots after 2 years of treatment. Measurements on fleeces and top from sheep with no apparent pigmented spots showed that this wool was generally free of pigmented fibres. In contrast, wool from affected individuals generally had high concentrations of pigmented wool fibres, with substantial pigmented lengths (means 20–40 mm) and intensely darkened, which related to the field records of black-grey pigmented skin spots. The amounts of dark pigmented fibres found in the processed top from affected fleeces ranged between 262 and 1293/kg. Based on these findings, sheep age is an important factor for inclusion in decision systems alerting wool buyers to the risk of hidden dark fibres. However, if adequate inspection of sheep during shearing is practical to isolate fleeces from sheep with black-grey pigmented skin spots in the fleece areas, then the risk level applied could be lowered or removed for the wool from the unaffected sheep.

Additional keywords: pigmented spots, old Merino sheep.


Acknowledgments

I thank Peter Flavel, David Little, and farm staff for the management and access to sheep at Parndana Research Centre. Several other staff assisted in the collection of field records. Debra Partington (BiometricsSA) undertook a preliminary analysis of data from the field inspections of sheep. Janice Altman undertook the dark fibre inspections of staple wool, and Annette Mackie and Tahera Pourbeik inspected the samples of wool top. I thank Roger Foulds and his team at CSIRO Division of Textile Physics (Ryde, NSW) for organising the processing of fleeces to top and measuring transmittance on the extracted pigmented fibres. Funding from Australian wool producers assisted the wool measurements.


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