TUBULE DENSITY, MOISTURE CONTENT AND MECHANICAL PROPERTIES OF DONKEY HOOF HORN
This study established new protocols for the collection, storage and preparation of donkey hoof horn samples prior to their subsequent analysis. Using these methods, normal values for moisture content, tubule density and mechanical properties for donkey hoof horn were established. Novel methods for investigating regional differences in these hoof horn parameters were also validated in this study. The protocols for, and calculations used in, establishing hoof wall moisture content were substantially reviewed in this study. There were significant differences between moisture contents of donkey hoof horn ascertained using different drying techniques. One technique, namely desiccation over phosphorus pentoxide, was subsequently chosen to be the most appropriate method for dehydration of hoof horn for analyses of moisture content. The moisture content of donkey hoof horn of 33% was found to be significantly higher (p<O.O1) than the 26% shown for horse hoof horn. Donkey and horse hoof horn are, in vivo, close to full hydration levels. This is a different situation to that previously believed to exist for the horse and may have important implications for the management of donkey hoofhom and the types of disease to which it is subject. The sorption and desorption isotherms for donkey hoof horn samples equilibrated over different saturated salt solutions showed hysteresis. It is thus necessary to know whether the moisture content of donkey horn samples following equilibration in a particular relative humidity environment has been achieved by sorption or desorption. The sorption and desorption isotherms for donkey hoof horn showed similar results to other keratinised tissues such as wool and head horn. Analyses were carried out on full hoof wall depth samples and also on partial hoof wall depth samples. These latter samples were known as zones, with zone 1 being the most outer part of the Stratum medium and zone 4 being the most inner part. There was a dorso-palmar increase in moisture content. There were significant differences in moisture content between all zones except between zone 3 and zone 4 for donkey hoof horn. A three zoned pattern of distribution of hoof horn tubules across the dorso-palmar depth of the hoof wall has been shown to exist for donkey hoof horn, compared to the four zoned pattern that is already known to exist for pony and horse hoof horn. These differences may reflect important differences in the mechanisms of hoof function. There was a positive correlation (0.92) between hoof wall depth and animal body weight (p<O.OO1). A regression analysis resulted in an R2 value of85%. Donkey hoof horn was shown to display Hookean properties during flexural three point bending. There was a significant inverse relationship between moisture content and mechanical properties of donkey hoof horn. Indeed, 96% of the variation in modulus was attributed to the effect of moisture content. The mechanical properties of horse hoof horn were thought to vary across the hoof wall. However, for donkey hoof horn, the use of a consistent level of hydration indicated that the mechanical properties do not vary across the four zones tested. There was a positive correlation (0.64) between tubule density and the moduli of samples when tested at full hydration (p<0.05), together with a positive correlation (0.60) between tubule density and the hydrated regain of samples equilibrated at 75% relative humidity (p<O.05). This study provided objective measurement of moisture content, tubule density and mechanical properties of donkey hoof hom Assessment of both clinical hoof problems, and the results of manipulation of nutrition or management of animals on hoof condition, can now be carried out objectively.
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