Clinical diagnosis of vitamin B12/cobalt (Co) deficiency is difficult due to the unspecific nature of the clinical symptoms. The apparent increase in vitamin B12 deficiency in New Zealand in the late 1990’s made it clear that health providers were very reliant on plasma reference ranges to diagnose deficiency. However, the lack of quantitative data of what these reference ranges represent in terms of supply of vitamin B12, has prevented a better understanding of the metabolism of vitamin B12 within sheep. This thesis describes the development of an experimental approach to measure vitamin B12 production and absorption in sheep. The model was then used to investigate whether the type of carbohydrate source affects vitamin B12 production and/or absorption. In the first trial (Chapter 4), an adaptation of the repletion technique of Suttle (1974) for copper was used. Previously vitamin B12 depleted sheep were maintained on a diet of 400 g DM meadow hay and 250 g DM crushed barley and which provided a daily intake of 0.03 mg Co. Sheep were intravenously infused with known quantities of vitamin B12 (0 – 200 nmol hydroxycobalamin/d) to determine whether a relationship exists between plasma vitamin B12 concentration and rate of entry of the vitamin into the bloodstream and to quantify the relationship. Eight ewes fitted with rumen and abomasal cannulae were used in a paired 4x4 Latin square design. Four levels of vitamin B12 were infused into the jugular vein for 4 d followed by recovery period of 17 d and the plasma responses measured during this period. Control animals maintained relatively stable plasma levels while levels in treated animals rose sharply within 4 h after the start of infusion. The responses were proportional to infusion rate with a highly significant difference in concentrations observed between treatments (P<0.001). Appearance of vitamin B12 in the plasma was quantified by the relationship Y(pmol/l) = 238 + 102x0.74 where x = infusion rate(nmol B12/d), R² = 0.945. Plasma levels declined rapidly on cessation of infusion and had returned to original pre-treatment levels by the end of the recovery period. The second trial (Chapter 5) quantified plasma responses in relation to dietary Co supply to the rumen. The same eight rumen and abomasal cannulated ewes were used in a paired 4x4 Latin square with 4 levels of intra-ruminal Co infusion in amounts ranging from 0 – 1 mg Co/d as CoSO₄, infused for 4 d followed by a 19 d recovery period. Plasma vitamin B12 response was measured as were concentration of vitamin B12 in abomasal digesta supernatant and digesta liquid flow, the latter using polyethylene glycol as liquid phase marker. Plasma concentration increased from approximately 300 pmol/l to 750 – 800 pmol/l, peaking at day 5 after commencement of infusions. Control animals infused with water maintained base-line plasma vitamin B12 levels around 250 pmol/l. Digesta liquid flow was estimated at 14.6 l/d. The results from Chapters 4 and 5 allowed estimates of vitamin B12 production and absorption. These results are discussed and efficiency of capture of Co into vitamin B12 from dietary Co intake was estimated to decrease from 8.4% to 0.74% as Co intake increased from 0.03 to 1.11 mg Co/d. Absorption coefficient was estimated from the relationships between abomasal vitamin B12 flow and plasma response. The absorption coefficient was calculated to increase from 7 to 10% as abomasal vitamin B12 flow increased from 108 to 142 nmol/d. The current animal model was subsequently used in the final trial (Chapter 6) to investigate whether the type of carbohydrate supplied in the diet influences vitamin B12 production and absorption. The same eight ewes fitted with rumen and abomasal cannulae were used in a 2x4 cross-over design. Half of the ewes were maintained on the basal diet and crushed barley while, for the remainder, the barley was replaced by 250 g of fructose:sucrose in a 80:20 mix during a 7 d period of adaptation. While on their respective diets, both groups were then infused with 0.3 mg Co/d for 6 d, a level chosen to optimise plasma vitamin B12 response. All ewes were then returned to the basal diet and barley for a 15 d recovery period after which treatments were reversed and the procedure repeated. Rumen pH, valeric, propionic, butyric, succinic, and acetic acid and ammonia concentrations were not significantly affected by diet. Digesta flow was 30% greater on a diet enriched with starch compared to sugar-enriched diet. There was an observed difference in vitamin B12 production. However there was no significant diet x time effect on plasma vitamin B12 concentration so any difference in production was negated by a difference in absorption. Carbohydrate supplied as water soluble carbohydrate or starch does not appear to influence plasma vitamin B12 concentration.
| Identifer | oai:union.ndltd.org:ADTP/270085 |
| Date | January 2009 |
| Creators | Ludemann, M. R. |
| Publisher | Lincoln University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://purl.org/net/lulib/thesisrights |
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