Claw quality is an important factor that influences the welfare and productivity of sows. Claw quality is evaluated by visual scoring for claw shape, shape dimensions, lesion scoring, and measurement of structural, physical, and biochemical properties of the claw horn.1,2 In sows, mainly claw lesion scores are evaluated to define claw quality, but other measurements, including claw conformation, horn growth and wear, and mechanical claw characteristics, are rarely evaluated. More recently, effect of diet on histological claw characteristics were assessed with or without partially substituting inorganic zinc (Zn), copper (Cu), and manganese (Mn) sources with their organic forms.3,4 Claw lesions are a common multifactorial disorder in sows, with malnutrition and floor type, among others, noted as predisposing factors.5,6 Claw lesions influence claw quality, but claw quality also influences the occurrence and severity of claw lesions. Furthermore, claw quality depends on the internal characteristics of the claw, including optimal horn production, which is influenced by a diffuse nutrient supply from the dermis to the avascular epidermis.2,7,8 An insufficient nutrient supply results in a disturbed diffusion of nutrients to the avascular epidermis. This negatively affects horn production, thereby increasing the susceptibility of the claw to damage from the environment.7,8 The structural, regulatory, and catalytic functions of Zn are related to horn production.7 However, results from previous studies, mainly in cattle, are inconclusive: reports range from no effect or a reduction in claw lesion and lameness scores with varying dietary Zn concentrations.9-11 In weaned pigs, claw quality was affected by dietary Zn level.12 Studies in sows did not assess the impact of increased dietary Zn concentration, but showed similar claw lesion scores, neither deterioration nor better scores, or better scores with (partial) substitution of inorganic Zn, Cu, and Mn sources by organically bound Zn, Cu, and Mn, 3,13-18 except in one study.19 Study duration may be important for detecting differences between treatment groups. A lack of effect of dietary Zn may have been related to an excessively short study duration: 12 months is the threshold reported in the literature.10,11,20 Claw quality may be affected internally by dietary Zn concentration, while floor type is an external factor in development of claw lesions.6 An increased occurrence of claw lesions is observed when sows are housed on fully or partly slatted concrete floors, whereas straw bedding seems to be positively associated with fewer and (or) less severe claw lesions.6,11,21 A rubber top layer on concrete floors appears to protect claws due to a cushioning effect.22,23 In a long-term study in sows, however, the risk of more severe claw lesions increased when sows were housed on a rubber floor.24
Therefore, it was hypothesized that both dietary Zn concentration and floor type would influence claw quality in sows. The objective of this longitudinal study conducted over three reproductive cycles was to evaluate the effect of dietary Zn supplementation on claw quality characteristics in sows housed on two different floor types during gestation.