An important factor for disease management
In intensive poultry production systems good foot pad health is crucial to obtaining high levels of animal welfare and high production yields. Often foot pad health is seen to decline over the production period. It is known that in intensive production systems suboptimal litter quality and high body weight are risk factors in maintaining good foot health. In broiler breeders poor foot pad integrity may subsequently result in an increase in mortality due to septicaemic infections, including infection of the heart valves (endocarditis), and joint infections (arthritis), or decreased egg production due to pain and discomfort. The most frequently isolated bacteria from these infections are staphylococci and enterococci, which are both part of the natural flora of the skin or the gut. In order to cause disease these bacteria need a port of entry to enter the blood stream of the host. This leads to the hypothesis that foot pad lesions may serve as port of entry for these infections. PROHEALTH has investigated the role of foot pad health in relation to development of disease caused by staphylococcus and enterococcus bacteria in broiler breeders. We followed four parent flocks throughout the whole production period (20-60 weeks) by post mortem and bacteriological examination and evaluation of the foot pads. The foot health of the flocks at the end of production was also investigated (Figure 1). The flocks exhibited normal performance regarding production and mortality, and no unexpected disease outbreaks were observed. The litter quality in all the flocks at the end of the production period were dry and loose, and with no history of major deterioration in quality. No systematic record of body weight was recorded in the flocks.
In total, around 60% of all the investigated birds had lesions in their foot pads. The lesions ranged from mild thickening of the skin (hyperkeratosis) to ulcers with tissue loss (necrosis) and/or infections in the foot pad (bumble foot). When the foot pad quality was considered in relation to age, we observed that the ratio of dead birds with foot lesions of any severity increased dramatically after 40 weeks of age, starting below 40% in young birds (20-29 weeks) and rising to almost 80% in birds more than 50 weeks old. This confirms that the foot health in broiler breeder flocks deteriorates dramatically with increasing age. Just before the flocks were sent to slaughter more than two thirds of the hens demonstrated lesions in the foot pads with ulcerations in about a third of the examined hens. Overall there was relatively large variation between the four flocks whether the foot pad lesions were observed in the dead birds or in live birds in the flocks just before slaughter. Similarly, death caused by staphylococci and enterococci infections increased throughout the production period, peaking at 40-49 weeks of age where almost 20% of the mortalities were due to these infections. The most frequent infection manifestations were joint infections (arthritis), sepsis, infections of the heart (endocarditis) and bumble foot.
To link the foot pad lesions directly to the findings caused by staphylococci and enterococci we performed a series of infection studies where foot pads were investigated for a role as port of entry for the bacteria (Figure 2). Deposition (inoculation) of bacteria in the dermal layer of skin of the foot pad led to lesions identical to the lesions we observed from the field. The vast majority of the birds receiving a high dose of staphylococci displayed lesions distant from the injections site (e.g. joints, liver, spleen and heart), whereas low doses led to less severe lesions in fewer birds. For enterococcal infections the overall appearance was comparable to the staphylococci infections, however fewer birds showed systemic lesions. All of the birds receiving either staphylococci or enterococci had considerable inflammation at the injection site in the foot, some with obvious abscess formation in the dermal layers of the skin. Furthermore Eschericia coli, the most common bacterial cause of death in intensive poultry production, were similarly investigated. When E. coli was injected in the skin of the foot pads none or minor lesions at the injection were demonstrated, indicating that E. coli primarily infects via the oviduct and airways.
Thus the link between foot pad integrity and generalised Gram positive bacterial infections was observed, with suggestions of strain and dose variation in the outcome of the infection.The nature of the foot lesions is being further characterised, in order to develop a scoring system for use in live birds during production.