This paper reports the relationships between isolated pigmented fibres in hogget Merino fleeces, the levels of pigmented fibres in processed wool from these fleeces, and changes in various types of visible pigmentation in young sheep. The sheep sampled were hogget Merinos classed within paternal groups on the basis of indicators of isolated pigmented wool fibres in the fleece, forming 17 batches of fleeces processed to top (combed sliver). There was a strong correlation (r > 0.95) between the counts of pigmented fibres from measurement of the raw wool and the top. The concentration of pigmented fibres in top was at least equal to that found in the raw wool grid sample. Most of the pigmented fibres removed from the tops were assessed as having the potential to cause problems in wool processing. Sheep with pigmented leg fibres had greater amounts of other types of visible pigmentation than sheep without pigmented leg fibres, at 1 or more stages from birth to 18 months. There were also differences in agerelated changes in pigmentation associated with presence or absence of pigmented leg fibres. Presence of pigmented leg fibres was the best indicator of isolated pigmented wool fibres in the fleece and processed top; however, this positive relationship was evident only in progeny of sires with a high degree of expression of leg fibre pigmentation. In this sample of sheep, which were crutched to remove urine stain, classing based on leg fibre pigmentation alone was sufficient to keep the levels of pigmented fibres below the often-quoted upper limit of 100 dark fibres/kg for tops used for products in which dark fibres affect acceptability. Other types of pigmentation were also associated but provided little additional indication of isolated pigmented fibres in the fleece. Pigmented leg fibres will be readily discernible at crutching and shearing.
The distribution and character of melanocytes in the wool-bearing skin of Merino sheep of known genotypes were examined by light and electron microscopy. In black Merino sheep (ww, homozygous recessive), melanocytes were localized within three regions of the skin: epidermal-dermal border, outer root sheath and follicle bulb. Melanocytes within these regions were found to be actively producing melanin, had numerous dendritic extensions and were able to transfer melanin to adjacent keratinocytes. In a black Merino sheep whose fibres were white due to an experimentally induced copper deficiency the melanocytes were amelanotic. In contrast, for both WW (homozygous dominant) and Ww (heterozygous) white Merino sheep melanocytes were observed only at the epidermal-dermal border of the epidermis. The melanocytes appeared also to differ in character containing less melanin, appearing less dendritic in shape and having a reduced ability to transfer melanin to adjacent keratinocytes. The gene for white fleece (W), therefore, appears able to regulate pigmentation in Merino sheep, at least in part, by controlling the location and activity of melanocytes within the wool-bearing skin.
Pyrite is easily oxidized, and therefore unambiguous evidence of detrital pyrite grains in metasediments is a significant constraint on when an oxygenated atmosphere developed. Compact rounded pyrite in the Witwatersrand gold reefs of South Africa has a detrital habit and is texturally equivalent to and spatially associated with detrital zircon and chromite. X‐ray precession photography reveals that petrographically featureless As‐poor grains are untwinned single crystals of high diffraction quality. This new evidence from crystallography is consistent with mechanically abraded pyrite from primary lode gold deposits, and excludes an origin by replacement of a pre‐existing detrital phase. Further evidence of a detrital origin for the compact rounded pyrite is afforded by isolated grains of arsenian pyrite displaying truncated As‐rich growth bands. The geographically extensive Witwatersrand fluvial conglomerates evidently had a matrix of quartz and pyrite sand and pyritic mud in their unconsolidated state and, thus, the late Archean atmosphere of Earth was likely essentially anoxic.
Various densities of black sheep (0, 2%, 9.5%, 21.4% and 50%) were run with white sheep for a period of 10 weeks. The groups were yarded on average once weekly. The number and lengths of melanin-pigmented wool and kemp fibres were measured in carded wool samples from the white fleeces. All groups containing black sheep produced white wool with higher levels of pigmented fibres (an increase of 8- to 64-fold) than the control group (P< 0.05). The extent of contamination of white wool by pigmented fibres increased with the density of black sheep. Both pigmented wool and pigmented kemp fibres occurred frequently in the contaminated wool samples and the fibres mainly had lengths less than 10 mm. The results provide evidence of the risks involved in the practice of including pigmented sheep in white sheep flocks.
White-skirted fleece wool from 68 piebald Merino sheep was divided into four portions that were sampled and measured for pigmented fibres. The piebald sheep were identified by the presence of pigmented fibre spots (usually one), varying in size from 2 mm diameter to over 50% of body surface area, and their location conformed to no particular pattern. The majority of samples for each portion (72-82%) had no detected pigmented fibres. There were 14.7% of piebald sheep with a concentration of isolated pigmented fibres (PFC) of at least 1 per 10 g scoured staples (taken to be the threshold of commercial importance) for their white fleece wool. While most PFC values were below the commercial threshold, there is a risk that some pigmented areas on piebald sheep may be missed during shearing. Of the various records taken for macroscopic pigmentation on the piebald sheep, only the scores for pigmented fibres at the horn sites (HSF) were significantly correlated (r=0.37; P<0.01) with PFC. The HSF scores were significantly correlated (P<0.05) with several other types of non-fleece pigmentation.
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