Development of an experimental approach of measurement of vitamin B₁₂ production and utilisation in sheep: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

Three trials were conducted to develop an experimental approach to measure vitamin B₁₂ production and utilisation in sheep. In the first trial, 10 halfbred ewes low in plasma vitamin B₁₂ were fitted with rumen cannulae, housed indoors and split onto two low Co containing hay diets. Doses of Co as CoS0₄.7H₂0 (0 -1mg Co) were injected intra-ruminally via the cannula. Responses were measured by plasma vitamin B₁₂. Responses peaked by day 2 and were proportional to the amount of Co injected. A fitted relationship model of the disappearance of plasma vitamin B₁₂ from the blood showed all treatments had common rate coefficients, suggesting vitamin B₁₂ utilisation/excretion from the plasma concentration is proportional over the range of peak plasma vitamin B₁₂ obtained. There was no significant effect of diet on production or apparent absorption of vitamin B₁₂ from the rumen. In a second trial, the sheep used in trial 1 were injected with an acute injection of vitamin B₁₂ (as hydroxycobalamin) into the jugular vein at rates ranging from 0.5 - 24 nmol vitamin B₁₂. Plasma vitamin B₁₂ response was again proportional to dose rate and the fitted relationship to decay showed a rate coefficient common for all treatments. Plasma vitamin B₁₂ values had returned to initial starting values within 24h after injection. Trial 3 was a chronic infusion of vitamin B 12 into the jugular vein for 48h. Infusion rates of vitamin B₁₂ (hydroxycobalamin) ranged from 2.5 - 2500nmol vitamin B₁₂/d. Plasma vitamin B₁₂ responses were proportional to infusion rates. A model of appearance plateau of vitamin B₁₂ against infusion rate was fitted. Peak responses from trial 1 (intra-ruminal Co injection) were plotted on the relationship between infusion rate and appearance plateau from trial 3 to give an equivalent infusion rate that would give the same plasma vitamin B₁₂ response for each Co dose. With information on vitamin B₁₂ flows from the rumen this model can be used to estimate vitamin B₁₂ absorption from the rumen in sheep.