Dr Natalie Meades: IBERS, KEHub, Aberystwyth University.

January 2024

 

The shearing of a sheep’s fleece is a welfare essential animal husbandry practice that helps to protect sheep from ectoparasites and from developing heat stress in the summer months.

Sheep’s wool is a useful product that is commonly used within the textile, building and horticultural industry. However, the price that Farmer’s receive for wool is very little. Therefore, there is great interest in valorising this product.

One area of interest is breeding sheep for improved wool quality. By improving the quality of wool this will potentially enable entrance into premium markets and therefore receive better returns.

With any breeding programme care needs to be taken with regards to any potential trade-offs that may occur whilst selecting for a trait. For example, it is important that selection is not made at the expense of economically important traits or at the expense of animal health and welfare.

Introduction

The shearing of a sheep’s fleece is a welfare necessity to protect sheep from ectoparasites (fly strike) and heat stress during the summer months. As a result, the fleece or wool is a by-product of meat or milk production. Wool is a versatile product that can have many uses, for example, wool can be used within the textile industry to produce carpets, rugs, curtains, linen, bedding and clothing. Moreover, wool can be used within the construction industry for insulating buildings, a study demonstrated the use of wool panels with densities of 25 / 92.5 kg / m3 to have a thermal conductivity of 0.040 – 0.041 W / mK. Furthermore, wool has been demonstrated to have promising use within the horticultural industry where it can be used as a mulch or for composting.

 

The Current Value of Wool in the UK

Although wool can be transformed into a variety of useful products, the price that UK farmers receive for wool is very low. As such, there is very little profit to be made from selling wool and it is often the case that farms either break even or not at all when the cost of shearing is taken into consideration. For example, the cost of paying contractors to shear, electricity to power shearing machines and not to mention the labour cost of gathering and preparing animals for shearing. To give an insight of this, the 2022 wool clip as reported by the  British Wool Board was 20p/ kg for core grades of Welsh Mountain wool. Moreover, core types from organic flocks achieved 70 p/ kg and organic Welsh Mountain types received 20 p/ kg. Whereas according to the National Association of Agricultural Contractors 2023 survey, the cost of shearing was estimated to be £1.65 / ewe and £3.10 / ram.

What determines the price of wool?

Wool in the UK is predominantly sold through the British Wool Board at auction. The price received is based on fleece weight, cleanliness and the British Wool Board grading system, in which there over 120 grades largely based on style and characteristic. The style of the wool is largely determined by; staple length, crimp, fineness, handle and lustre which have been refined into six style categories (Figure. 1). Within each style the wool is graded based on quality as determined by; origin (e.g. from a hogg or ewe), colour, staple strength, uniformity, kemp, grey fibre, cotts and first/ second shearing and then payment determined. As such different breeds have different wool styles and characteristics and therefore have different payments associated (Figure. 1). However, it is often the case that sheep with low fibre diameters (low micron counts) receive the higher payments

Figure 1: a) Different wool categories and examples of British breeds associated with them b) all 60 UK sheep breeds and their categories, images are from British Wool Board.

Valorising UK Wool

There is great interest in valorising wool. One such method is to breed sheep for improved wool quality and as such have multi-purpose producing sheep. In other words, sheep co-producing meat and wool rather than just focussing on one product. Improving the quality of wool may enable farmers to enter premium markets, receive higher payments and therefore see better returns. Research in this area is limited in the UK, however a 12 month research project called Fabulous Fibre was recently announced in January 2024. The project is funded by the Department for Environment and Rural Affair’s (DEFRA) Innovation Programme Research Starter 3 competition as part of DEFRA’s Farming Innovation Programme which is delivered in partnership with Innovate UK. The 12-month project will aim to investigate the feasibility of improving fleece quality and improving the value of wool through breeding and genetics, where focus will be given to improving wool quality by reducing the micron count of wool from finer wool quality breeds in the UK. To fully understand the possibilities of this it is first important to understand the biology and development of wool follicles and fibres. 

Follicle and Fibre Development

A sheep’s fleece is made up of a number of fibres which develop from follicles associated with sebaceous glands. The biology and development of wool follicles and fibres is explained from information obtained from Doyle, et al. (2021). Follicular development occurs during foetal development from epidermal cells within the skin. This process consists of a number of waves. The first wave occurs at approximately 65 – 100 days gestation and involves the development of primary follicles. The second wave occurs at approximately 90 – 130 days gestation and involves the development of secondary follicles and the final wave occurs at approximately 100 – 130 days gestation and involves the branching of secondary follicles. The skin follicle population is thought to be complete at around four months post-partum.

As mentioned above, wool fibres are produced within follicles that lie within the dermis and epidermis of the skin. The follicle has three major zones that are important for the development of wool fibres. These are the follicle bulb, zone of keratinisation and the zone of final hardening (Figure. 2). Cells within the follicle bulb multiply at a rapid rate and migrate distally where they synthesize keratin (high sulphur amino acid fibre protein) from amino acids sourced from nearby blood vessels. Wool proteins are then formed from gene transcription and translation mechanisms. The inner root sheath which surrounds fibre cells is also formed within the follicle bulb, this hardens and forms a dye in which the fibre cells are cast through and shaped. When the fibre cells approach the end of the follicles keratinisation zone the sheath cells are resorbed and the fibre cells dehydrate and harden following the production of disulphide bonds between sulphur atoms on cysteine residues in the keratin protein. The resultant wool fibre appears with various crimps, this is a result of differences in the hardening of the fibre on one side compared to the other. 

Schematic diagram of a wool follicle as presented by Yu, et al. (2009).

What Determines the Quality of Wool and Can this Be Genetically Selected For?

Fleece Weight

The price of wool is described by the unit’s p/ kg of product; therefore, fleece weight has a bearing on the payment received. For example, the heavier the fleece the higher the payment to a certain extent. A paper discussing the wool follicle and skin characteristics of Merino sheep, describes the equation below for calculating the quantity of wool produced by a sheep per year and therefore fleece weight. From the calculation it is evident that fibre diameter, follicle density and fibre length are all important characteristics for determining fleece weight. Moreover, the relationships between these characteristics can determine the quality of the wool. 

W = (L x N x CSA x S x A) x 365

W    = Weight

L      = Fibre length growth rate (µm/ d)

N     = Follicle density (follicles / mm2)

CSA = Mean cross sectional area (µm2)

S      = Specific gravity of wool

A      = The fleece bearing skin area (mm2)

Follicle Density

Follicle density is thought to be one the main characteristics that influences the quality and quantity of wool. Follicle density can be defined by the total number of follicles per unit area of skin and the ratio of secondary to primary follicles. As such, total skin area characterised by body size and surface area have a bearing on this. Not only that, the degree to which the branching of secondary follicles occurs can also determine follicle density. Moreover, the branching of secondary follicles is thought to be important for determining wool quality where this process can determine various wool characteristics such as, the ratio of primary to secondary follicles, fibre diameter, fibre length and clean fleece weight.

Follicle density is known to vary from breed to breed and to be genetically controlled. Therefore, there is interest associated with this trait within breeding programmes targeted at improving the quality of wool. An example of this can be seen in previous selective breeding programmes associated with Merino sheep. Merino sheep have high quality wool characterised by fibres of typically 15 cm and low fibre diameters of around 20 µm. Moreover, follicle density is high (up to 60 / mm2) with a total population of approximately 107 – 108 follicles. This is all predominantly resultant of selective breeding programmes. Furthermore, selective breeding programmes have resulted in reduced size differences between primary and secondary branched follicles and increased the abundance of secondary branched follicles. As such, the majority of the Merino fleece is derived from secondary branched follicles resulting in fleeces that have fine uniform fibre diameters.      

Fibre diameter

Wool fibre diameter is a key measure of wool quality and is routinely used by the sheep industry, where it is measured as the mean diameter of greasy wool fibres in micrometres or microns (µm). Fibre diameter is known to affect the thickness of fibres, fabric mass per unit and to influence processing qualities, degree of entanglement during scouring and incidence of fibre breakage. As such fibre diameter can influence price, where low micron fibres tend to receive higher payments. Furthermore, wool fibre diameter is thought to be associated with the morphogenesis and development of wool follicles in sheep skin. Moreover, it has been demonstrated that a negative genetic correlation exists between fibre diameter and follicle density, therefore there is interest in reducing fibre diameter by increasing follicle density. However, low fibre diameters are often associated with lower clean fleece weights, although this is variable and therefore paves the opportunity to identify individuals with low fibre diameters and high clean fleece weights in selective breeding programmes.

Merino sheep are renowned for having low fibre diameters, as such research has generally focussed on this breed in terms of improving wool quality. Moreover, there has been interest in countries such as New Zealand for breeding Merino sheep for ultra-fine (13 – 16 µm) wool, to reach premium markets. It is suggested that the combination of low fibre diameter and high fleece weight is generally found within sheep with high wool follicle densities and high ratios of secondary to primary wool follicles. A study in Merino sheep in New Zealand aimed to breed yearlings with a mean fibre diameter of <16 µm and breed adult ewes with a mean fibre diameter of <17 µm without compromise to fleece weight, live weight or reproductive performance over an eight-year period. The trial involved an intensive screening process to establish a foundation flock with a low fibre diameter (based on fibre diameter BLUP breeding value) and then collected data from 2000 subsequent progeny over five birth years based on a 70-sire group. The results of the trial demonstrated that the intensive selection and subsequent creation of an open nucleus to be a suitable method for selecting individuals for low mean fibre diameters and that there were no compromises to live weight or fleece weight

Wool Length

Wool length is also thought to be an important characteristic in determining wool quality. It has been demonstrated that the gene fibroblast growth factor five (FGF5) can be an inhibitor of hair length in a range of species including humans, mice, donkeys, cats and dogs by having an effect on the hair cycle. A study using CRISPR/ CAS9 pronuclear microinjection to modify the FGF5 gene in Dorper sheep observed sheep to have dysfunction to the FGF5 gene and as a result have longer wool length. In a further study, it was discovered that Dorper sheep with dysfunction to the FGF5 gene had increased fine-wool and active hair-follicle densities. As such, this gene may be of interest in breeding programmes.    

Summary

Shearing is an animal welfare necessity to protect sheep from ectoparasites and heat stress. The resultant product from shearing is wool, which is a useful product that can be used by a variety of industries. However, the price that farmers in the UK receive for wool is poor. As such there is interest in increasing the value of wool, one of which is to improve the quality of wool so that it can reach premium markets and therefore receive better returns. Therefore, there is interest in producing multipurpose sheep, that is sheep that produce both high quality meat and wool. This in term involves breeding sheep for low fibre diameters and high clean fleece weights, which are largely influenced by follicle density and the ratio of secondary to primary follicles which are developed during foetal development. However, it is important to take into consideration that genetics only play a certain part and that external factors such as the environment and nutritional status can also affect wool quality. Likewise, with any breeding programme it is important that traits are not selected for at the expense of economically important traits or at the expense of animal health and welfare.


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