Dairy cow lameness : biotin, lipids and the structural integrity of hoof horn
This thesis describes in detail the fatty acid composition of both the solvent extractable and covalently bound lipids of bovine hoof horn from foetal calves, pre-ruminant calves and adult dairy cows by thin layer chromatography, gas liquid chromatography and mass spectrometry. Hoof horn from sound cows was found to contain more very long chain fatty acid (VLCFA) than that from laminitic cows. VLCFA were present in foetal hoof horn, indicting de novo synthesis of these fatty acids in the foetus. Light microscopy of the development of the sole epidermis showed that there is rapid development in the second half of gestation. Oral supplementation of pharmacological doses of biotin (20mg/cow/day) over 6-12 months in adult dairy cows significantly increased the proportion of non-hydroxy fatty acids with chain lengths of C18-C22 compared to unsupplemented control cows. In the main trial of this thesis, pre-ruminant calves were either biotin depleted (by feeding avidin) or biotin supplemented for 100 days compared to control calves. Significant biotin depletion and supplementation were achieved. Calf growth, plasma glucose and non-esterified fatty acid concentrations and hoof growth and wear were not affected by biotin status. The dry weight of the exungulated hoof horn capsule of the biotin depleted calves was greater than that of the biotin supplemented and control groups when adjusted for calf liveweight. Both the living and the cornified layers of the sole epidermis of the biotin depleted calves were deeper than for the biotin supplemented or control calves. Sole epidermis of the biotin depleted and control calves was investigated by light and electron microscopy. No differences in the expression of the suprabasal, differentiation associated keratins 9 and 10 were seen between the biotin depleted and the control calves as assessed by immunohistochemistry and gel electrophoresis followed by Western blotting. There was no evidence of the presence of the hyperproliferation associated keratin 16 by these methods, indicating that the epidermis was not physically damaged. The biotin depleted calves showed significantly increased epidermal proliferation as measured by the expression of Ki-67. Analysis of electron micrographs using Image Pro Plus showed a significantly increased occurrence of ‘holes’ in the mature stratum spinosum and stratum corneum of the biotin depleted calves compared to the control calves. The conclusions of this thesis were that there were differences in the chain lengths of fatty acids from hoof horn lipids of sound and laminitic cows.