Problems caused by dung contamination are not to be sniffed at

It has been estimated that in Australia alone, 12 million cow pats1 hit the ground every hour! Multiply that to account for the world's cattle population and that's an awful lot of dung! But how does all this poo affect the leather industry? Well, it is difficult to know where to start because dung contamination of hides and skins causes so many problems for the tanner. When cattle are housed in a confined area together for prolonged periods, dung contamination of the hide is inevitable as the cattle lie in a slurry of their own faeces and urine. Their legs and belly area become caked in this mixture that sticks to the hair with alarming tenacity. Whilst the dung mixture is still moist, bacteria begin to grow rapidly. This sets up a reaction with the urine causing it to release ammonia which is an irritant. This in turn raises the pH of the dung causing the digestive enzymes that it contains to become active and begin to digest certain components of the skin itself. The result is an intense irritation of the skin that is essentially similar to nappy rash in babies. As a result of this prolonged irritation, the skin attempts to protect itself by forming a thickened epidermis (hyperkeratosis). When the hide is processed into leather this appears as a rough grain surface with finger-like projections and distorted hair follicles. In addition to this disfigurement, the grain surface often dyes a slightly different colour to the surrounding areas making it difficult to produce aniline leather. Apart from the problems caused by the irritating effect of dung on hides, the presence of dung on the hides during leather processing also presents difficulties. When dry, dung is extremely hard and difficult to rehydrate - we used to make the walls of houses out of it for this very reason (wattle and daub). Consequently, it is extremely difficult to wash off. If sizeable clods of dung remain after soaking it can cause the blades of the fleshing machine to cut into the hide and cause damage. If dried clods of dung are mechanically pulled from the hide it can cause grain damage. Effluent problems Once the dung has been removed from the hides and skins, it has to be disposed of. In the UK at least, water authorities have strict limits for contaminated wastewater and the cost of effluent treatment and disposal is high. Bacterial problems Dung contains an alarming number of bacteria. When the hides are soaked, the water activates bacterial activity causing the bacteria to proliferate in the soak liquor. This is aided by blood and other soluble proteins that are washed out from within the hides that provide an excellent nutrient broth for bacteria to grow in. Unless these bacteria are controlled by the use of biocides, putrefactive damage can occur to the hides. Chemical usage In the early part of the leather-making process, chemicals quantities are calculated as a percentage of the weight of the raw hides. If those hides are carrying several kilos of dung, then tanners are using far more chemicals than they really need to. Prevention Obviously, the best way to overcome the problems caused to tanners by dung on hides is for farmers to keep their cattle cleaner. In 1996 there was an outbreak of food poisoning in Scotland that sadly killed 17 people and caused hundreds of others to be very ill. This food poisoning was found to have been caused by the transfer of E Coli bacteria from dung on the cattle hide being transferred to meat during the preparation of the carcase at the butcher's. This disaster led to the introduction of legislation in the UK that prohibits the presentation of dirty animals for slaughter. This reduced the number of cattle entering slaughterhouses with more than 4.5kg of dung attached to their hides from more than 40% to less than 10% within two years2. This could not have been better news for tanners - no more dirty hides we thought! But sadly, all was not as good as it seemed. Bedding cattle on straw has been found to be highly effective at keeping cattle cleaner, but straw is expensive and in some areas difficult to come by. Consequently, many farmers do not necessarily keep their cattle any cleaner, but remove the dung just before they are sent for slaughter by clipping the dung off with shears. So, not only do hides still have the damage caused by the irritation that dung causes, but they also have cuts caused by the mechanical clippers.