High dietary biotin levels affect the footpad and hock health of broiler chickens reared at different stocking densities and litter conditions

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The occurrence of footpad and hock lesions, forms of contact dermatitis, with regard to product quality and animal welfare has recently become a major concern in the broiler industry (Kjaer et al., 2006; Abd El‐Wahab et al., 2013; Bassler et al., 2013). This is an ulcerative skin condition caused primarily by high litter moisture (Mayne et al., 2007a; Youssef et al., 2011a,b), a problem that tends to be more pronounced at high stocking densities (HSD; Feddes et al., 2002; Bessei, 2006). In severe cases, the lesion may be painful to impede walking and feeding activity (Haslam et al., 2006) or be harmful to health by becoming a gateway for bacterial infections (Bassler et al., 2013). Besides, it has a negative impact on production (Shepherd and Fairchild, 2010; Ventura et al., 2010) because the damaged feet cannot be sold and the affected birds are slow to gain weight. The relationship between stocking density and footpad or hock burns is very complex. Although some studies failed to detect an adverse effect (Martrenchar et al., 2002; Sirri et al., 2007; Meluzzi et al., 2008a), it is widely accepted that HSD exacerbates the condition (Dozier et al., 2005, 2006; Meluzzi et al., 2008b), mainly due to the increased water intake (per unit area) and excreta or litter moisture (Feddes et al., 2002).
One strategy that can be used to prevent footpad and hock dermatitis is to improve skin integrity in the vulnerable period. One potential nutrient or bioactive molecule for achieving this is biotin, which plays an essential role in skin formation, maintenance and repair as a coenzyme for many carboxylases in protein synthesis and fatty acid metabolism (Whitehead, 1988; Mayne, 2005). In practical diets, a marginal biotin deficiency has been associated with footpad lesions in broilers (Harms and Simpson, 1975; Harms et al., 1977; Oloyo, 1991). In commercial conditions, more biotin is required to reduce contact dermatitis, rather than only to support growth. For example, increasing dietary biotin level (2000 μg/kg of diet) above normal recommendations for broilers reduced the severity of footpad dermatitis in spite of continuous exposure to wet litter (35% moisture, Abd El‐Wahab et al., 2013). An interaction between biotin supplementation and litter quality may exist. In turkeys, supplying the diet with high concentrations of biotin alleviated the footpad burn on dry litter, but not on wet litter (sprinkling water to the litter, Harms and Simpson, 1977; 73; % moisture, Youssef et al., 2012). Little is known, however, if supplemental biotin has a relationship with the detrimental effect of HSD on skin condition. Dawkins et al. (2004) reported that stocking density has little effect as long as a favourable environment is maintained. Indeed, the moisture content of litter is the primary factor leading to footpad and hock lesions (Mayne et al., 2007a; Youssef et al., 2011a,b), even at low stocking density. These raise the possibility that biotin fortification may well improve the paw and hock quality of broiler chickens stocked at high densities, at least when the litter is kept dry.
The objective of the present study was to determine whether feeding a higher level of biotin than is normally present in commercial diets would minimize the occurrence of footpad and hock burns in high‐density broiler production, particularly with good litter management to avoid wet litter. Since predisposition to contact dermatitis has been different among breeds and across age (Tucker and Walker, 1992; Kjaer et al., 2006), the fast‐growing genotype during the grower period (4–6 weeks old), being the most reactive, was evaluated. Additionally, live performance, carcass composition and litter quality were measured.
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