Pigmented Fibres Research Articles

Incidence and relationships of black skin spots in the fleece area and pigmentation traits in commercial Corriedale flocks

The presence of pigmented fibres (PF) in the wool prevents access to high quality markets. Pigmentation traits such as black spots in the fleece area and pigmentation scores in non-fleece areas might be correlated with PF. The aim of this study was to assess the incidence and variation of black skin spots and pigmentation scores of nose, hooves and ears of sheep, and their phenotypic relationships, in 13 randomly selected commercial Corriedale flocks. During 2006 and 2007, data from 2448 animals (10–15% of each flock) of different ages (1- to 5-years-old) and broad genetic origins (different studs) were collected at shearing. Pigmentation in non-fleece areas was assessed using a subjective scale of 1 (light) to 5 (black). Black skin spots were identified in fleece areas and percentage of PF on its surface was determined using a subjective scale of 0–5. Distribution of nose pigmentation scores was symmetric and unimodal, whereas they were skewed towards a high score in hooves and a low score in ears. Presence of spots increased with the age of animals. In nose and hooves, a reduction in pigmentation with age of animals was observed. Important differences between flocks and animals were detected for all pigmentation traits. Spots and pigmentation traits in non-fleece areas were phenotypically associated. This study on pigmentation traits of commercial Corriedale sheep indicated that there is a noticeable phenotypic variation among animals and flocks, suggesting the existence of an underlying genetic variation in these traits.

Fluorescence and coloration of grey hair

Grey hair samples were collected from 11 individuals and separated into un-pigmented and pigmented fibres (International Hair Importers). Fluorescence measurements were obtained by using a double-grating fluorescence spectrophotometer and a bifurcated fibre optics accessory to measure the spectra directly from the surface of hair at various distances from the fibre root. Colour measurements were carried out by using a Hunter colorimeter. The fluorescence spectra of un-pigmented hair obtained by the excitation at 290 nm show a peak at 356 nm [tryptophan (Trp)], and multi-peak emissions in the range from 395 to 500 nm. A significant variation in the Trp emission intensity at 356 nm vs. the intensity of emission in the 395-500 nm range was observed for hair collected from various individuals with yellow coloured hair producing stronger relative emission in 395-500 nm range. Quantitative measurements of coloration and the calculation of the Yellowness Index (YI) showed linear correlation between YI and the ratio of fluorescence intensities I(440)/I(356) The spectra obtained by excitation at 320 nm showed the emission peaks at 395 nm (unidentified), 420 nm (N-formylkynurenine), 460 nm (kynurenine), and 495 nm (3-hydroxykynurenine), which are the products of oxidative or metabolic conversion of tryptophan. Un-pigmented, yellow hair showed a build-up of the fluorescence band corresponding to 3-hydroxykynurenine at 495 nm. The data also showed the fluorescence quenching effect of melanin resulting in the lowering of the fluorescence intensity of pigmented hair. The spectra obtained at various positions along the fibres demonstrated gradual photo-decomposition of hair chromophores during their lifetimes. This was indicated by a decrease of Trp fluorescence intensity, which was relatively fast (8.10(-4)-1.5.10(-3) [day(-1)] as calculated for hair obtained from various individuals) for un-pigmented hair and slower for pigmented hair. A decrease in Trp emission was accompanied by an increase in the yellow coloration toward the ends of un-pigmented fibres.

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

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.

Pigmentation relationships among young Merino sheep and their processed wool

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.

A new scheme for describing horse coat colour

A new descriptive scheme of horse colours is proposed with four dimensions: (1) pigmentary pattern (which deals with the symmetric partition of eumelanic — black or brown — and phaeomelanic — red — pigmented areas (five different types)); (2) eumelanic type (black or brown); (3) pigment alteration (a modification of pigmentary appearance inside the hair or an intermixing of white and pigmented fibres); and (4) white designs (when the white patches are clearly distinct from the coloured ones). The advantage of this new descriptive scheme are: (1) a better connection with the biological and genetic realities; (2) a more accurate description of the very numerous different colour phenotypes: and (3) a more assimilable international language.

Pigmented fibres in white-skirted fleece wool from Piebald Merino sheep

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.

The association between non-fleece pigmentation and fleece pigmentation in Corriedale sheep

ABSTRACTThe phenotypie associations between scores for various types of non-fleece pigmentation and concentration isolated pigmented wool fibres in the fleece (experiment 1 and 2) or the piebald phenotype (experiment 3) were studied in Corriedale hogget ewes. These sheep were selected on the basis of either degree of nose skin pigmentation (experiment 1), presence or absence of pigmented fibres at the horn sites (experiment 2) and presence or absence of the piebald phenotype (experiment 3). Among affected fleeces the concentration of isolated pigmented fibres (PFC) had high correlations (0·96 and 0·97) with the proportion of staples affected, which indicates that when PFC is high the isolated pigmented fibres are widely distributed throughout the fleece. Three types of non-fleece pigmentation had significant (P < 0·05) positive correlations with PFC in experiments 1 and 2. These were pigmented skin on the nose lips (0·23 and 0·18; P < 0·05), pigmented fibres at the horn sites (0·34 and 0·30; P < 0·01) and pigmented fibres on the legs (0·36 and 0·29; P < 001). The pigmentation of skin or fibres in non-fleece areas was predominantly black/grey and there were usually significant (P < 0·05) positive correlations between the various types of non-fleece pigmentation. In experiment 3, piebald sheep were found to have higher scores for black/grey fibres on the ears (P < 0·001), face (P < 0·01) and horn sites (P < 0·05) and for black/grey skin under the tail (P < 0·01) than non-piebald sheep.

Comparison between Merino sheep homozygous (WW) or heterozygous (Ww) for white fleece on the incidence of isolated pigmented wool fibres and types of non-fleece pigmentation

Merino sheep known to be homozygous (WW) or heterozygous (Ww) for white fleece were examined for isolated pigmented fibres and various types of non-fleece pigmentation on the adult sheep or pigmented halo-hair on the birth coat.There was no significant difference (P>0-05) between WW and Ww sheep in the occurrence of isolated pigmented fibres. Nevertheless, 17% of the fleece samples contained varying concentrations of pigmented fibres; up to 510 per 10 g scoured staples. Of the various types of macroscopic pigmentation recorded, the scores for pigmented halo-hair (lamb) and pigmented fibres on the horn sites (adult) were the most strongly correlated (r= 0.39 and 0.30, respectively; P<0.001) to the concentration of pigmented fibres in fleece samples. Heterozygous sheep had slightly more black/grey pigmentation for bare skin areas on the nose lips and around eyes ( P< 0.001) or under tail (P<0.05) and in the hooves (P<0.05) than WW sheep, but these differences arc unlikely to be of practical relevance.

A note on the occurrence of isolated melanin pigmented fibres in the white fleece wool of Corriedale sheep

ABSTRACTThe occurrence of melanin pigmented wool fibres in the skirted white fleece wool from 1-year-old Corriedale ewes, having either least (group 1), most (group 3) or an intermediate level (group 2) of black nose skin pigmentation, was investigated. Thirteen of the 87 fleeces analysed had the equivalent of 10 to 389 isolated pigmented fibres per 100 g of scoured wool. The mean diameter of the pigmented fibres was similar to that of the fleece specimens analysed and they occurred singly or in small groups within individual staples. Large numbers of isolated pigmented fibres in fleeces were widely distributed, and constitute a serious problem of identification by visual inspection. Fibre darkness and the number of fleeces found with pigmented wool fibres were two measurements which showed a significant association (P < 0·001 and P < 0·05, respectively) with nose skin pigment group. With one exception from group 2 the results support the suggestion that the usual selection for dark nose skin in this breed may be antagonistic to selection for a white fleece. The pigmented lengths of fibres were found to be independent of nose skin pigment group.