The skin is the largest organ of vertebrates, making up 16% of body weight. It plays a key role in defending the body by forming an impermeable barrier with sweat and oil glands that inhibit bacterial growth. The skin also receives stimuli, stores fat for insulation and energy, and produces keratin and melanin. Hides and skins from mammals have a similar histological structure and are primarily made of water, proteins, and fats. The skin has two main layers, the epidermis and dermis, with a subcutaneous layer beneath. Cattle hides account for 70% of raw materials for leather production. Various defects can reduce the value of hides by causing damage before, during, or after slaughter

1. Skin
The skin is the largest organ of a
vertebrate body (16% of BW) that
plays a key role in body defense.

2. How the skin defend the body:
• It forms an impenetrable barrier
• Oil & sweat glands give the skin surface a low
pH of 3-5 that inhibit growth of many
microorganisms
• Sweat contains lysozyme which digest
bacterial cell walls
• It prevents excessive loss of water through
evaporation

3. 2. Receive stimuli from the environment
3. Subcutaneous fat is a form of stored
energy and provide insulation against cold
4. The epidermis of the skin forms various
skin appendages (hair, hooves, glands),
produce keratin (essential for protective
function of the skin) & melanin (protect Vs
UV irradiation)

4. 5. 99% of all the leather produced
worldwide is made from the hide/skin of
mammals
• The histological structure of hides/skins
from all mammals is more or less the
same

5. Hides & Skins Structure

6. Structure of the skin:
• The skin is made up of 2 main layers:
(i) The epidermis
(ii) The dermis (corium)
• Beneath the dermis is a connective tissue
layer (subcutis or hypodermis)
• The hypodermis is connected to
aponeuroses or periosteum

7. • The interface between the epidermis &
dermis
is uneven [made up of projections of the
dermis
(dermal papillae) and epidermis
(epidermal
ridges)]

8. Structure of the skin

9. Chemical Composition of skins:
• The main constituents of freshly-flayed
animal hide/skin are:
(i) water 64%
(ii) proteins 33%
(iii) Fats 2%
(iv) mineral substances 0.5%
(v) Other substances 0.5%

10. The DM of the skin contains:
• 50% Carbon (C)
• 25% Oxygen (O)
• 7% Hydrogen (H)
• 17.8% Nitrogen (N)
• 0.2% Minerals

11. • The epidermis & hair consist of the protein
keratin
• Keratin give mechanical strength &
flexibility to the skin (insoluble &
waterproof the skin surface)

12. • Keratin is readily attacked by bacteria &
easily disintegrated by alkalis (e.g. caustic
soda, lime & sodium sulphide or
hydrosulphide)
• – this is the basis of the unhairing
process in the tannery

13. • The predominant angle at which the
collagen fibres are interwoven can indicate
the properties of leather
• Upright and tightly woven fibres can lead
to firm hard leather with little stretch
• Horizontal & loosely woven fibres can
lead to soft strechier leather

14. Sources of hides & skins:
• Hides & skins are a (necessary) by-
product of
animal husbandry therefore quantity of raw
hides available worldwide for leather
production is limited, being directly linked
to
demand for other animal products

15. • The primary objective of the livestock
producer
is to improve quantity & quality of meat
&/or
milk therefore requests from tanners to
improve quality of hides/skins are
generally
disregarded

16. • Cattle hides account for 70% of raw
material for leather production
worldwide followed by sheepskins
and then goatskins
• Pigskin leather production is limited to
few areas

17. • Other species used: horses, donkeys,
camels & game animals
• Non-conventional sources: crocodiles,
monitor lizards, snakes, ostriches & fish
(these provide expensive luxury
leathers forming a small share of the
market)

18. Raw hide/skins defects:
• Defects reduce value of raw hides &
consequently the leather made from it
• Defects are caused by:
- diseases
- external damage before slaughter
- damage arising during slaughter
- damage arising during flaying
- damage caused by improper transport
- inadequate preservation

19. Hide damage before slaughter:
• Mechanical damage:
- Brand marks
- Scratches (thorns, barbed wires)
- Whips/goads/pitchforks/chafe-marks
• Diseases:
- warts, boils, skin diseases (LSD), skin
parasites (warbles, ticks, mites etc.);
Burns caused by dung & urine; Genetic
defects (e.g. excessive number of vertical
fibres)

20. Hide damage during slaughter:
• Flaying Damage:
- Gashes/gauges by knives
- floor dragging damage
- grain cracks caused by hammer
flaying
- scalding damage in pigskins

21. Hide Damage after Slaughter:
Storage & Transport Damage:
• Putrefaction
• Blood & Rust stains
• Drying damage (splitting due to too rapid
drying of hides)
• Insect damage
• Damage due to poor packaging