The wool proteome and fibre characteristics of three distinct genetic ovine breeds from Portugal
Graphical abstract
Introduction
Animal fibres are valued and important commodities for textile industries worldwide. The highest value fibres include mohair and cashmere from goats (Capra hircus), alpaca (Vicugna pacos), qiviut from muskox (Ovibos moschatus) and of course wool from sheep (Ovis aries). The latter is by far the most important animal fibre, being widely used by the textile industry with an estimated 1.160 million kg of clean raw wool produced globally by more than 1.163 billion sheep in 2015 [1]. Wool has historically played a major role in the economies of countries such as Portugal or Spain in the 15th Century and the UK, Australia and New Zealand since the onset of the industrial revolution in the 18th Century.
Wool is nevertheless an inconsistently applied convenient name for a quantity of fine or uniform fibres from a variety of mammals (e.g., sheep, goats, camelids and rabbits) for the textile industry. However, at an industrial scale, wool is obtained only from the ovine (Ovis aries) species. Numerous breeds are available worldwide in a plethora of production systems that include the production of wool, but also milk and meat. Ovine breeds are divided into two major categories: hair breeds and wool breeds, with the diameter of individual fibres in the latter being much finer than the former. Typically, hair sheep are characteristic of tropical regions of the world whereas wool sheep are found mostly in temperate regions. In turn, wool sheep are recognised as having three categories: coarse, mid-micron and fine wool. The textile industry uses essentially fine wool for garments and the others for the manufacture of other goods such as rugs or carpets. The present lines of domesticated sheep were derived from the mouflon (Ovis orientalis) over 10,000 years ago [2]. It is believed that initially, all domestic sheep were hair sheep, with a smaller proportion of finer under hairs, as seen in most of Europe's oldest breeds, such as those in Scandinavia that have remained unaltered since the Viking age. It is thought that the fine fleece, as found in the merino sheep, was a result of a gradual narrowing of fibres, particularly in the primary follicle. Coupled with this, was the loss in the importance of the primary follicle, resulting in a switch in the secondary:primary follicle proportion from 1:20 to one precisely the opposite. Present evidence suggests that the fine fleece developed at some point in the later first century AD [3].
Despite its relatively small geographical size, Portugal in SW Europe, accounts for fifteen different autochthonous sheep breeds. These, in turn can be divided into three major groups: Churro, Bordaleiro and Merino with respectively 7, 5 and 3 breeds. Churro breeds are very ancient and are believed to have remained unaltered since pre-Roman days. They are typically farmed in small-scale mountain production systems, being very tolerant to harsh climates and poor-quality pastures. On the contrary, Merino breeds are more recent (early medieval age) and are farmed in commercial farming systems in the southern plains, mostly in the Alentejo region. Finally, Bordaleiro breeds are mostly dairy sheep and used extensive dairy production systems in Central Portugal. Of the three types of fleece, Churro breeds produce a very coarse type of wool (over 80 μm) with long and hanging fibres whereas Merino breeds produce a high-quality fleece with a very thin (8–25 μm) curly fibre. Finally, Bordaleiro breeds produce an intermediate type of fleece with a thickness of 25–40 μm [4]. Fig. 1 shows examples of the three different breeds with their distinctive fleece and wool differences (Fig. 2). In the present production conditions in Portugal, only Merino wool has any commercial value and the industry tends to favour white fibres and devalue pigmented wool. Nevertheless, the production of certified products and the establishment of specific alternative niche markets from autochthonous breeds are growing in importance [5].
Proteomics is a set of techniques of growing importance in the field of animal and veterinary sciences [6], albeit with some limitations, particularly when making comparisons to model species [7]. Its use has been demonstrated in numerous areas, from meat science and technology [8] to the study of tick-borne disease virulence [9] or the goat mammary gland physiology [10]. During the last two decades, proteomics has been extensively used to study the wool protein composition and its relation to quality. Indeed, since the earlier works [11], numerous studies have been published on this aspect. These include the proteome of the wool cuticle [12], the effect of nutrition on the merino wool proteome [13] or the wool fibre morphogenesis [14]. The subject has furthermore been extensively reviewed [15] and readers are directed to it for further information.
Interestingly, fibre/wool proteomics has seldom been used to study species and breed differences. Indeed, Thomas and co-workers conducted the first interspecies comparison of morphology, ultrastructure, and proteome of keratin fibres in different mammal species: sheep, goat (mohair), rabbit and alpaca [16]. More recently, proteomics has been used to differentiate sheep from goat fibres [17]. However, concerning breed comparison studies, to the best of our knowledge, very few studies seem to be available. Our research teams have recently published a study that contrasted the differences between the white and black merino breeds, highlighting differences mostly at the level of high-sulphur proteins or HSPs and high-glycine-tyrosine proteins or HGTPs [5].
The objective of this study is to compare the three different ovine types with respect to their wool quality traits, namely fibre diameter and curvature, as well as the protein abundance patterns and for this a label-free approach was adopted [18]. Our ultimate goal is that of understanding the effects of protein composition on wool quality traits in three very diverse types of sheep that are in turn representative of the major sheep populations existing in Southern Europe and, hence, what consequences this might have for the conventional and alternative textile industries. Given that proteins make up 98% of the total fibre content by weight [19] and 85% of these are the keratinous proteins [20] we chose to focus on the keratin proteome in this study.
Section snippets
Animals and sample collection
Methodologies were adapted from Plowman and co-workers [5]. In this study, we sourced Merino (Merino Branco breed) wool samples from commercial farms in the Évora District in Alentejo region (Southern Portugal), Bordaleiro (Serra da Estrela breed) wool from the Coimbra District in the Beira Interior region (Central Portugal) and Churro (Churra da Terra Quente breed) wool from the Vila Real District in the Trás-os-Montes region (Northeast Portugal). These were randomly obtained from ewes shorn
Macroscopy and microscopy studies
There were considerable differences in appearance between fibres from the three breeds and this was reflected in the results from the OFDA analysis (Table 1). The CTQ fibres were notable for their coarse, straight fibres, more characteristic of kemps or guard hairs and these had the highest fibre diameter (mean of 43.8 μm) and lowest curvature (mean of 25.8°/mm) of the three breeds. At the other extreme were the MB fibres that had the lowest fibre diameter (mean of 24.4 μm) and highest
Discussion
Transmission electron microscopy suggests that CTQ and SE wool contain a similar cast of hair types, underhairs (wool) and various diameter guard hairs, higher by comparison to those normally found in Merino breeds. Within such hair types there is much similarity in fibre ultrastructure with the primary difference being in the size and elongated cross-section profile of the underhairs from CTQ sheep. While the SE underhairs, which have a more circular cross-section, are similar in organisation
Acknowledgements
Authors are grateful to Mr. Tiago Perloiro (ANCORME – Merino Breeders Association, Évora, Portugal) and Mr. João Madanelo (ANCOSE – Serra da Estrela Breeders Association, Oliveira do Hospital, Portugal) for kindly supplying respectively the MS and SE wool samples. Authors acknowledge the artwork by Mr. Simão Mateus (Lourinhã Museum, Lourinhã, Portugal) used in Fig. 1 and the graphical abstract, and for helpful discussions with Evelyne Maes and Alasdair Noble. Funding for this project was
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