Leather – Cows, Sheep and Goats
What is leather?
Leather is a general term for an animal skin which has been chemically processed, or ‘tanned’, to make it resistant to decay.1 Left untreated, skin begins to decompose within just a few hours of being removed from a body.2 Tanning processes a raw skin into a stable material which is used worldwide to create a vast range of products.3
The primary sources of skin for the leather industry are the 3.44 billion4 cows, sheep and goats who are farmed across the globe each year.5 Rather than being a by-product of the meat industry, their skins hold the status of a commodity in their own right,6 being worth up to 15% of the total market value of each individual animal.4
The European leather industry produces a quarter of the world’s leather,7 employs 52,000 people8 and has an annual turnover of nearly £7 billion.7 £700 million of this is generated within the UK alone.9 The aggregate value of world leather production has been estimated at close to £28 billion, making animal skins an extremely valuable raw material and a major contributing factor to the profitability of the meat industry.3
Leather goods are the end product of an industrial supply chain which begins with the production and handling of the industry’s ‘raw materials’, in the form of animal farming and slaughter.3
How is leather produced?
Slaughter
In the UK, farmed animals are transported to a slaughterhouse where they are stunned using electrocution, gas or a captive bolt.10 The unconscious animals are then shackled and hoisted on to an overhead moving rail where they are ‘stuck’,11 severing the major blood vessels within the throat or within the chest.10 They are then left to ‘bleed out’ until death occurs.10 This lasts upwards of 30 seconds for cows and 20 seconds for sheep and goats.12
In religious slaughter, animals may not receive prior stunning and once restrained, the major blood vessels within their throat are severed using a single movement of an undamaged blade.10 Unstunned animals remain restrained until they have ‘bled out’ and lost consciousness.10 In some instances, post-cut stunning may take place during the slaughter of cows and in Halal slaughter, stunning methods that would not in themselves cause death, may be deemed acceptable.10
The high cost of running regulated slaughter houses means that in less economically developed countries the use of unlicensed abattoirs is not uncommon.6 Pre-slaughter stunning by use of a hammer to provide a manual blow to the head is still practiced in developing countries and in many places cows are immobilised by using a knife to sever the spinal cord. 13 This causes collapse but not loss of consciousness, leaving the animal fully aware up to and during their slaughter.13
Flaying
Once bleeding has slowed, handling of their body begins11 and their skin is removed in a process known as ‘flaying’.6 This takes place using one of three methods: pulling by hand; cutting by hand using knives; or mechanical flaying, using an automatic hide puller.6 Skinning begins while the animal is hanging from the shackling chain used during their slaughter.11
Cows remain hanging while their horns are removed and their head is skinned and cut from their body.14 They are then positioned within a dressing cradle, where their legs are skinned and severed at their knee joints.14 Their skin is cut along the centre line of the underside of their body, from their throat up to their tail and the skin is removed from their flanks and lower chest.11 Their udder is skinned and they are partially hoisted, raising their rear end to allow for skinning of their vent and tail.11 They are then fully hoisted to allow their entire skin to be removed.14
Sheep and goats are flayed either horizontally or vertically.11 When flayed horizontally, they remain shackled while their free hind leg is skinned and their hoof removed.11 A stick known as a gambrel is then inserted into their Achilles tendon to suspend their body, while their shackled leg is released and skinned before also being attached to the gambrel.11 Their skin is cut along the midline of their body, from their throat to their tail.11 A frame is used to open out their front legs, exposing their chest, neck and flanks for skinning.11 The frame is suspended from a hook, hanging the animal by all four limbs as their hindquarters are skinned.11 Their front legs are detached from the spreader frame and their feet are cut off, so that their entire skin can be pulled from their body.11
When skinned vertically, sheep and goats are turned on to their backs and are cut along their front legs from their knuckles upwards.11 Their cheeks, neck and shoulders are skinned, their head is amputated and their hind legs are cut from their knuckles up to the base of their tail.14 Their legs are skinned and they are then hoisted using a gambrel as before.14 Their flanks are flayed and their skin is pulled from their body, down over their spine and to their head.11
Collection of skins
Skins are collected from the slaughterhouse on the day of slaughter, typically by local hide markets who classify and weigh the skins and preserve them through salting or chilling.15 The skins are then sold and transferred on to a tannery.9 Alternatively, if a slaughterhouse is linked with a tannery, skins are transferred directly there, bypassing the use of a hide market and eliminating the need for initial preservation processes.2
Due to the rate of bacterial growth and skin decomposition, no more than a few hours are left between slaughter and either preservation of skins or the start of their processing.2
Beam house operations
On arrival at the tannery skins undergo what are known as ‘beam house operations’, where they are prepared for tanning by removal of tissue and hair9 through the following processes:
Soaking – to remove blood, dung, curing salt and soluble proteins.9
Degreasing –sheep skins are chemically degreased.9
Fleshing and trimming – to remove extraneous tissue.10
Dehairing and pulling – to remove hair or wool from the skins surface.10
Liming – painting the flesh side of the skin with a depilatory, usually consisting of sodium sulphide and lime.10 Liming chemically dissolves hair and the epidermis,9 removing degraded proteins and fat tissue and opening the structure of the skin.5
Deliming – the lime depilatory is removed by treating the skin with an acidic solution.9
pH - dilute sulphuric acid is used to adjust the pH of the skin prior to tanning.9
At this stage, the partially processed skin is referred to as a ‘pickle pelt’.10
Tanning
Tanning is the process by which pickle pelts are processed into leather.6 Tanning treatments displace water from the skin9 and irreversibly stabilise the collagen fibres,6 increasing their resistance to heat, water and decomposition.9
Chrome tanning (using trivalent chromium salts) is the most commonly used method of tanning.7 The skins are treated with these chemicals in large rotating drums which are designed to facilitate mechanical agitation and speed up chemical reactions.10
Skins that are chrome tanned and left wet are known as ‘wet blue’.5 This is sometimes traded as an intermediary product and sold on to other businesses to complete the tanning and manufacturing processes.6
Prior to post-tanning, the skins are trimmed and split horizontally to produce a separate grain layer and a flesh layer.6
Post-tanning operations
The chemicals used during tanning are washed from the skin6 and the leather is then retanned, dyed and oiled to produce the desired colour, texture and elasticity. 10 Any injuries suffered by the animal during their life are masked during post-tanning operations by buffing, shaving and dyeing of their skin.2 The leather is then dried, prior to being finished.6
Finishing operations
The processes employed during finishing manipulate the final appearance, texture and functioning of the leather.9 The skin is mechanically flattened and the grain may be set,10 embossed and ironed,6 or processed to produce suede.10
A surface coat of pigments is then applied to protect the leather from damage and to create a final colour and shine.11
Environmental pollution
The leather industry generates air, liquid and solid waste pollution during the processing of raw hides and skins into an imperishable material.6 The waste products generated during the manufacture of leather are capable of causing significant environmental damage.8 Only 15 % of the chemicals used during tanning are retained in the finished leather, while the residual 85% has to be dealt with as waste.16
Liquid waste can pose a significant problem, as solvents can contaminate bodies of water through surface run off and groundwater permeation.9 Less soluble compounds, such as chlorinated solvents, are a particular problem as they are slow to break down, enabling them to accumulate within the environment and persist for extended periods.9 There is a close correlation between chrome tanning and the environmental impact of leather processing.16
The production of leather is in itself, an environmentally costly process. The processing of skins into leather requires an extremely high input of water,2 for instance 8,000 litres of water are required to produce just one pair of leather shoes.17
Uses of leather
The primary use of leather is in the manufacture of footwear, which consumes approximately 65% of all leather produced.2 Each year an estimated 11 billion pairs of leather shoes are manufactured, with a gross wholesale value in the region of £94.7 billion.2
Skins taken from cows and calves are used in clothing5; upholstery5, including car interiors2; accessories like handbags, watchstraps and briefcases18; and sporting equipment, such as motorcycle jackets,18 cricket pads and football boots.
Skins taken from sheep and lambs are used in clothing, such as sheepskin jackets, boots and also as shoe linings; to produce suede; for wool-on products, such as rugs; in book binding; and for chamois leathers.10
Uses of leather by-products
The processing of skins generates many additional products which are used within a vast range of manufactured goods, such as animal feed, photography equipment, cosmetics, and fertilisers.8 The sale of these products all adds to the economic profitability of the leather industry.
- Fleshings are used in compost.20
- Wool and intact hair are used in fertiliser, compost, plant pots, cosmetics, pharmaceuticals and for felt.2
- Limed splits unsuitable for tanning are sold for sausage casings, or hydrolysed to produce soluble gelatine which can be sold into the food, photographic and pharmaceutical industries.2 Alternatively the hydrolysate can be neutralised using phosphates and then used in fertiliser, as a coagulant in rubber or as a plasticiser in concrete.2
- Trimmings from untanned skins are used to produce glue.21
- Delimed hide splits are dried to produce dog chews2 and raw trimmings are used in animal feeds.18
- Untanned wastes and waste fleshings are mixed with tannery sludge2 and farming waste to be used in methane production.21
- Collagen taken from solid leather waste is used to manufacture leather board, artificial leather and poured insulation.21
Statistics
- Globally there are more than 1.5 billion cows, 1 billion sheep and 827 million goats.19
- Over 250 different chemicals are used in the production of leather.2
- Only 15% of the chemicals used in the tanning process are retained by the finished leather - the remaining 85% enters waste streams.7
- The production of leather requires a high input of water.2 It takes 8,000 litres of water to produce one pair of leather shoes.17
- A cows skin weighs on average 19kg.5
- In 2005-2007 more than £40 billion was made from the global trade in cows, sheep and goats skins, leather and leather products.5
- The aggregate value of world leather production is close to £28 billion, which is higher than that of meat production.3
References
- International Union of Environment (IUE) Commission of International Union of Leather Technologists and Chemists Societies. IUE document on recent developments in cleaner production and environmental protection in world leather sector. Basal, Switzerland; IUE 2008 www.iultcs.org/pdf/All_IUE_documents_2008.pdf
- Food and Agriculture Organisation of the United Nations (FAO). Hides and skins and skins and leather commodity profile and strategy for development. Rome, Italy; FAO 2001www.fao.org/docrep/meeting/003/Y0019e/Y0019e.htm (accessed 6th October 2010)
- Farm Animal Welfare Council. Report on the welfare of farmed animals at slaughter or killing. Part 1: Red meat animals. London: Defra Publications; 2003
- Hoekstra, A.Y. & Chapagain, A.K. Globalization of Water Oxford: Blackwell Publishing; 2008