Vitamin D Metabolite Effects on Mineral Dynamics and Bone Physiology in Ruminants

Abstract

<p>The dynamic properties of bone are foundational to stabilising the availability of phosphorus and calcium within the bodies of humans and livestock alike. In order to facilitate improved commercial management of breeding cattle in Australia's phosphorus deficient far north, this thesis sought to address the role of Vitamin D₃ metabolites as supplements to both control phosphorus and calcium excretion and to accelerate bone growth in ruminants. Supplementation with metabolites of Vitamin D₃ is a novel approach to improving animal wellbeing, as these bioactive compounds have been shown to improve blood calcium and phosphorus concentration, reduce mineral excretion and to improve bone status.</p> <p>With this in mind, an approach that focused on supplementing ruminants with these compounds to increase mineral absorption and bone accretion was assessed. The hypothesis was that these feed additives could increase phosphorus accretion efficiency and the promotion of bone growth, which in turn could provide the basis for efficient widespread supplementation of livestock, their improved reproductive health and increased financial returns.</p> <p>The study described in this thesis investigated the effectiveness of a negative dietary cation-anion difference (DCAD) diet on bone loss in ruminants over 28 days, followed by assessing the effects of dietary supplementation with supraphysiological doses of 25(OH)D and 1(OH)D (Alfacalcidol) over 84 days. The findings and implications of this experiment were as summarised below:</p> <p>• A negative DCAD diet (-66.2mEq/kg) over a 28-day period did not affect bone mineral density or biomarkers of bone loss.</p> <p>• Supplementation of Merino ewes with 1mg 25(OH)D per day over an 84-day period led to a:</p> <p>• Sustained increase in serum 25(OH)D concentrations</p> <p>• Increase in plasma calcium and phosphorus concentrations</p> <p>• Decrease in plasma magnesium concentrations</p> <p>• Decrease in calcium and phosphorus excretion</p> <p>• Increase in plasma bone-specific alkaline phosphatase concentration</p> <p>• Increase in mean bone mineral density of approximately 6% </p> <p>• Supplementation of Merino ewes with 2μg 1(OH)D per day over an 84-day period lead to: <p> Increase in plasma phosphorus concentration Increase in plasma phosphorus concentration</p> <p> No significant changes to biomarkers of bone metabolism or bone mineral density</p> <p>These results support the hypothesis that dietary supplementation with supraphysiological doses of 25(OH)D is a safe way to improve mineral status and bone mineral density in ruminants.</p>