Effects of dietary biotin on the physiology, anatomy and mechanics of pony hoof horn
Reilly, John D.
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A feeding experiment involving match-paired Treatment and Control groups of four ponies each was designed and conducted, under Home Office Project Licence number 60/01439, to test the null hypothesis that: "Dietary supplementation with biotin at a dose level of 0.12mg/Kg BW daily has no effect on the physiology, anatomy or mechanics of pony hoof horn"Biotin supplementation caused a significantly higher growth and growth rate of horn at the midline dead centre of the wall for Treatment compared to Control ponies (p<0.05 by Students t-test). The pair of two older animals in the trial had significantly lower hoof growth when compared with the rest (p<0.05 by ANOVA). No significant difference was found between feet for these parameters and so the left fore foot of each animal was used to provide material for anatomical and mechanical studies.Quantitative methods for measuring anatomical features which may have a functional significance such as tubule density, absolute areas and area fractions of hoof wall components, were devised. These methods were then used to give normal values for these parameters in the Control group and compared with those for the Treatment group.Hoof horn stratum medium (SM) was found to consist of four distinct zones as defined by tubule density (TD). This was new, quantitative, anatomical information. The zones were referred to as Zones 1,2,3 and 4 and were of approximately equal dorso-palmar depth into the hoof wall. In terms of their location within the depth of SM within the hoof wall, Zones 1-4 could then be respectively referred to as:Zone: Approximate dorso-palmar location within depth of stratum medium Z1: 'outer''; Z2: 'outer middle'; Z3: 'inner middle'; Z4: 'inner'. From this it was proposed that the pony hoof wall may function as a quadri-laminarply.In a follow-up study, a similar four-zoned pattern of hoof wall TD was also confirmed for horses.There was an effect of biotin supplementation on tubule density with treatment animals having a significantly higher tubule density in Zone 4 of the SM (PcO.Ol by Mann- Whitney U Test).There was an effect of biolin supplementation on tubule marrow sizes. Treatment animals had significantly smaller mean tubule marrow sizes compared with Control animals (p<0.01 by ANOVA). This distinction was found to be due to a significant difference between Treatment and Control animals in the two younger pony pairs and the differences were found in Zone 1 of the SM only.The area fraction ratio of tubular to intertubular horn was found to be 1:3 and not 1:1 as had been estimated by other workers in the past..The material stiffness of pony hoof horn was calculated from beam stiffnesses given in 3-point bending at 3 different moisture contents: 'fresh', 'fully hydrated' and 'dry'. There was no treatment effect on moisture content in any of these states, nor on material stiffness in the fresh and dry states. However, biotin-treated horn was significantly stiffer (p<0.05 by Mann-Whitney U Test) in the fully hydrated state.Correlations between physiological, anatomical and mechanical properties were investigated using a Pearson correlation coefficient matrix. Significant correlations were found to exist between some zonal hoof wall anatomical parameters, between hoof wall stiffness and bodyweight and hoof wall stiffness and age of pony. Stiffness of the hoof wall was also significantly correlated with tubule cortex size and tubule cortex volume fraction in Zone 2 of the hoof wall and with marrow size in Zone 4..In another follow-up study, the effect of another oral supplement (an evening primrose oil mixture, EPOM) was assessed in Army horses. Twelve horses were paired as closely as possible according to sex, age, weight, height and colour and then one from each pair was randomly allocated to treatment or control groups. The treatment group received 30mls of oral EPOM per day for approximately five and a half months, otherwise the nutrition and management regimes were the same for all horses. No significant differences (p >0.05) were seen between treatment and control groups for hoof horn growth or growth rate. However, there was a significant difference (p < 0.05) in hoof horn growth, within the treatment group only, between weeks four and eight after the start of supplementation. This revealed that the hoof capsule is capable of different growth responses when the equid is supplemented with different nutrients.No significant differences (p > 0.05) were seen between treatment and control groups for any of the lipid fractions measured for the stratum medium from clippings of the hoof wall in these horses. However, there were substantial differences in perioplic horn lipid analyses with significant increases (p < 0.05) in cholesterol esters and partial glycerides and a highly significant reduction (p <0.001) in free cholesterol in the treatment group compared to the controls following EPOM supplementation.Finally, preliminary work was started on Finite Element Analysis (FEA) and modelling at the macro- and micro- levels of structural organization of the donkey hoof wall because this is a useful means of predicting the effects of a change in hoof horn material or morphological properties, on the whole hoof capsule.