Magnesium absorption from the large intestine of sheep : This dissertation was submitted in partial fulfilment for a Bachelor of Agricultural Science Degree with Honours at Lincoln College

Abstract

In a 5 x 5 Latin square design trial 5 mixed age ewes, fitted with ileal caecal T-piece cannulas, were offered a pelleted low Mg (1.0g Mg/kg DM) diet at maintenance levels for 2 months during mid pregnancy. 230ml water with 0, 0.5, 1, 2 or 4g Mg/d was infused into the distal ileum. Absorption of Mg from the large intestine was estimated from the change in urinary Mg excretion and in plasma concentration of Mg. The magnitude of increase in urinary Mg ranged from 1.6x pretrial output after water or water +0.5mg Mg/d infusions to 2.8x pretrial output when infused with water +4g Mg/d, There was evidence that the absorption mechanism from the large intestine was becoming saturated at the larger rates of infusion (2 and 4g/d) of Mg in that the relationship between the amount absorbed and infused was curvilinear, The percentage of infused Mg that was being absorbed fell from 18.2% to 6.9% when Mg infusion rates increased from 0.5 to 4g Mg/d. In a second 2 x 4 factorial design trial, using the same sheep, increasing the amount of water infused with 4g Mg/d from 230ml to 2300ml had a negative effect on urinary Mg excretion. The results show that Mg can be absorbed from the large intestine in significant amounts and suggest that an active transport mechanism is likely to be involved. However, low water (230ml) infusions appeared to enhance Mg absorption from the large intestine indicating the importance of water transport.