Studies of vitamin B12 metabolism in young lambs : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

A trial to determine the requirement of young lambs for vitamin B12 and the efficiency of absorption of orally ingested vitamin B12 was conducted using 26 Coopworth X Dorset Down lambs. These lambs were collected at birth. Six of the lambs were slaughtered at the beginning of the trial. The livers of these lambs were weighed and analysed for vitamin B12. The remaining twenty lambs were split into five groups of four. The lambs were fed the same basal milk diet but were subjected to differing doses of cyanocobalamin. Groups A, B, C and D were offered an additional 4, 8, 16 and 64ug cyanocobalamin/lamb/day respectively, orally in milk which supplemented a basal level of dietary vitamin B12 ranging from 87ug to 95ug after Denkavit was added to the diet. Total intakes of vitamin B12 plus added cyanobobalamin were 176, 240, 430, and 1410ug. Another group of four lambs received no additional cyanocobalamin orally but received daily intramuscular injections of 8ug cyanocobalamin/lamb. Due to problems associated with the synthetic milk diet, lamb intakes were low and therefore growth rates were less than expected. Six lambs died or were destroyed during the trial. After three weeks, blood samples were taken from the remaining lambs prior to slaughter. The livers were weighed and analysed for vitamin B12. Total liver vitamin B12 content increased with increasing dietary intakes of vitamin B12. The change in total liver vitamin B12 began to plateau with total intakes greater than 430ug (0.03ug/ml). However, because no significant difference in concentration of vitamin B12 in the liver was found, between control and treatment lambs the total vitamin B12 content of the livers of lambs killed after three weeks was significantly higher (p=0.019) than that in the control lambs. Liver weights increased significantly (p=0.001) It was calculated that the efficiency of absorption of ingested vitamin B12 was at least 7 percent, based on change in liver B12 content and it could in fact, have been very much greater because the group in which vitamin B12 was injected were unable to store greater quantities than those given vitamin B12 by the oral route. This work raises questions about the ability of suckling lambs to store vitamin B12 absorbed from milk.