The vitamin B12 and Se status of lambs during their transition from milk-fed monogastric to grazing herbivore

AIM: To estimate how the lamb’s transition from a monogastric at birth to a grazing ruminant at weaning affects its dietary intake of trace nutrients from milk and pasture, and to determine whether its vitamin B12 and Se status changes during that period. METHODS: We reviewed published reports of field trials in New Zealand where flocks were managed on mixed sward pastures without additional supplements. Information on intakes of milk and pasture was drawn from studies of suckling lambs grazing with ewes for up to 20 weeks. We calculated the quantities of vitamin B12, Co and Se ingested and absorbed by lambs between birth and weaning. Trace nutrient status was based on concentrations of vitamin B12 in serum and Se in blood. Six studies met our inclusion criteria regarding age of lambs, supplementation and sampling frequency. In each, blood had been collected at regular intervals from birth to weaning. Changes over time in concentrations of vitamin B12 and Se were analysed using regression procedures. RESULTS: Estimated Se intake increased from approximately 5 μg/day near birth to 25 μg/day near weaning, but Se absorbed was less variable, being approximately 10 μg/day. Estimated vitamin B12 intake near birth was approximately 8 μg/day and increased to 90 μg/day by weaning, with the amount being absorbed increasing from 0.8 to 9 μg/day. Concentrations of trace elements in unsupplemented lambs among the six studies varied from deficient to adequate. Linear regressions indicated that there was little change in concentrations of vitamin B12 and Se between birth and weaning in four studies (p>0.05), and mean concentrations measured at docking did not differ from those at weaning in four studies where this could be assessed (p>0.1). CONCLUSIONS AND CLINICAL RELEVANCE: From newborn to weaned, a lamb’s physiology develops from monogastric to ruminant. The change in diet from milk to pasture presents markedly different chemical forms and concentrations of some trace nutrients. Despite this, the vitamin B12 and Se status of the unsupplemented lambs in these studies changed little during their transition period. This finding supports early monitoring of lambs’ trace element status. If a trace element deficiency is detected in lambs at or before docking, then administering supplements may be appropriate. If status is found to be adequate, then it will likely remain so until weaning, at which time the animals’ trace element status should be re-evaluated.