Food pad lesions reflect on bird health and welfare. It deserves more attention for ethical reasons and consumer desires. What is the cause and what can be done about it?
By Dr Amr Abd El-Wahab and Prof Dr Josef Kamphues, University of Veterinary Medicine Hannover, Germany
Foot pad dermatitis (FPD) has been known as a common problem in poultry production for many decades. Recently it attracted additional attention in terms of animal welfare, food safety and also consumer protection, since predisposing conditions for foot pad diseases are influenced by infections of the gastrointestinal tract and may also be related to zoonoses.
FPD is basically a type of contact dermatitis affecting the plantar region of the feet, with lesions surrounded by a reddening of the foot pads as a first symptom, followed by discolouration and hyperkeratosis, often in combination with erosions and necrosis of the epidermis, with deep ulcers occurring in severe cases. Furthermore, the lesions can be a gateway for bacteria which may spread haematogenously and might impair product quality. It has been indicated that broilers with severe FPD show reduced weight gain, which has been suggested to be a result of pain induced inappetance.
Causes of foot pad lesions
The aetiology of FPD is complex; it is an interaction of different factors. Some of these are related to management and housing including litter quality, management and type of litter. Furthermore, FPD is related to dietary factors. Finally, diseases could interfere with FPD caused by various gastrointestinal infections. Birds spend most of their productive life in close contact with the bedding/litter material. It is commonly accepted that litter moisture is a significant factor in the onset of FPD.
Recent studies however stated that pure water (without excreta) alone is already sufficient to produce severe lesions on the foot pads. Standing on wet litter has been suggested to soften the foot pad and to become more prone to damage, predisposing the birds to develop FPD. It was noted that the first marked increase in FPD lesions in turkey poults occurred after experimental exposure for only 4 h/d to a ‘critical litter moisture’ of 35% (i.e. 350 g water per kg mixture of litter and excreta).
Poor litter quality is considered nowadays a welfare problem in modern poultry production and hence research should focus on developing measures for upgrading litter quality. There is no doubt that wet litter will increase the prevalence and severity of FPD. Thus, all factors that affect the litter quality (especially moisture content) directly or indirectly are of special interest. But a critical question should be allowed: Is litter really the right focus?
Litter is a mixture of bedding materials with increasing amounts and proportions of excreta. At the end of the fattening period the proportion of excreta will exceed 90%, which means that less than 10% is litter material. During production the excreta (faeces and urine) releases its water content to the air which in turn is transferred out of the barn by ventilation. This underlines the importance of ventilation and arises the question what factors influence the water release from the excreta and/or the mixture of litter with excreta and the transfer to the air above the litter surface. It is well known that “layers of excreta” on the litter surface impair the process of drying markedly. What role does the “physical structure” of excreta - particle size and proportion of rough particles that present surfaces – play on the drying process. There is no doubt that wet litter induces FPD but why doesn’t the litter get dry easily?