pododermatitis in broilers

The broiler is a domestic animal genetically-improved for fast growth and muscle deposition, resulting in fragile limbs (feet and legs). Pododermatitis (Translator's notice: called by the authors in Portuguese foot callus) is a lesion in the foot pad commonly found in broilers grown on moist, caked litter (Santos et al., 2002) as a result of direct foot pad-litter contact. The younger, the heavier the bird the higher then incidence of the problem.
In accordance with Borges (2006) the use of old litter for up to for consecutive times, a popular practice among many broiler producers, promotes moisture and caking, thus contributing to increase the incidence of foot pad lesions, even if a low stocking density is used. Muniz (2006) stated that one indicator of animal welfare is the absence of carcass lesions, particularly pododermatitis, since these problems are closely related with housing and management conditions.
The feet, carcass parts that in the past had a low commercial value, are now increasing their price given the preference in some markets, like that in Asia, so that attention to this type of lesions is now more and more required. The purpose of this study was to evaluate the influence of heat stress (HS) on the incidence of pododermatitis in broilers at 35 and 42 days of age.

The study was undertaken in the Poultry Sector, College of Agrarian and Veterinary Science (FCAV), São Paulo State University (UNESP), Jaboticabal, São Paulo, Brazil, using 500 one-day-old Cobb broilers which were placed in two climate-controlled chambers at a temperature of 33°C  ±2°C (gradually decreasing as per bird age/ thermal comfort requirements) at a stocking density of 10 birds/m², on new wood ss litter, 10 cm deep. Water and feed were provided ad libitum. in order to obtain the desired ambient temperature, infrared lamps and coolers coupled to thermostats were used. The birds in one of these chambers were subjected to phases of HS, that lasted for 24, 48, or 72 hours. The first HS phase was started by adjusting the temperature inside the chamber to 32°C ± 2°C on day 35 of age, while the birds in the control chamber were maintained at thermoneutrality (TN) (24°C ± 2°C). At the completion of each HS period, 12 animals per treatment were taken, stunned, and slaughtered in the experimental processing plant, FCAV, UNESP.
After 72 hours, the internal temperature of the chamber was adjusted back to TN, staying so until day 42 of age, when the HS chickens were subjected again to a new HS phase (32°C ± 2°C). The control chickens were subjected to 21°C ± 2°C.
The feet of the birds killed were separated and categorized in accordance with the methodology recommended by McWard and Taylor (2000) based on visual observation, using the following scores: 0 - no lesions; 1 - small lesion; 2 - moderate lesion in one or both feet; and 3 - extensive lesion in one or both feet. The experimental design was completely at random, with two treatments (HS/no HS), and 4 lesion scores.

At 35 days of age, the non-HS chickens had a lower foot pad lesion incidence, and score 0 (no lesions) prevailed (Figure 1). In this group, some birds showed pododermatitis lesions, but they were less frequent/less severe than those in the HS chickens.

Figure 1. Percent food pads with lesions among the broilers subjected or not to heat stress (HS) at 35 days of age, as per lesion scores

 

The lesions considered serious (score 3) were seen in less than 10% of the animals selected for slaughter, in the HS group, while no score 3 lesions were seen among the controls, whatsoever.

Figure 2. Foot pads of broilers as per lesion scores at 35 days of age

Source: personal collection.

Figure 3 shows the per-lesion score categorization of the food pads of birds killed at 42 days of age. In the non-HS controls, score 0 (no lesions) prevailed; in addition, no score 3 lesions were found. In the HS birds, a higher incidence of small and moderate lesions was observed, when compared with 35-day-old birds, with a considerable increase in score 3 lesions, in 11% of the HS birds that were slaughtered.

Figure 3. Percent pododermatitis in the foot pads of broilers subjected or not to heat stress (HS), at 42 days of age, as per lesion scores

The difference between the lesions in the controls and those in the HS group, can be explained by the poor quality of the litter in the HS group, in agreement with Medeiros et al. (2005), who found that, under severe HS, animals increase their water intake thus producing more fluid feces, resulting in increased litter moisture and decreased water absorption capacity. If these conditions remain, the moistening/drying cycles in the litter promote caking thus favoring the presentation of contact pododermatitis (Medeiros et al., 2008), adversely affecting the development of the birds.

Based on the results reported herein, it can be concluded that heat stress exerts an indirect influence on the presentation of pododermatitis in broilers. Flocks grown in hot regions can show a high incidence of condemnations at processing, as a result of contact pododermatitis, with the consequent economic losses for the industry.

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Muniz EC. 2006. Influência da densidade populacional sobre o peso médio, percentual de calo de patas e histomorfometria da bolsa cloacal em aves (Gallus gallus).Dissertação (Mestrado em Ciência Animal), Universidade Federal do Mato Grosso do Sul. Campo Grande, 34p.

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