Changes in the availability of dietary copper to young lambs associated with age and weaning

Abstract

SUMMARY64Cu and an indigestible 103Ru-labelled marker were administered into the alimentary tract of six artificially reared lambs on four occasions, 28 and 14 days before weaning and 15 and 42 days after weaning. The ratio of 64Cu: 103Ru excreted in the faeces was used to measure the apparent availability of Cu.Mean Cu availability decreased from 71·0 ± 3·7 to 47·2 ± 7·8% immediately before weaning and to 10·8 ± 1·4% 15 days after weaning.The relationship between availability (y, %) and age (x, days) prior to weaning was described by the equationWhen half of the lambs were given abomasal doses of 64Cu + 103Ru 42 days after weaning, the mean Cu availability was 21·4±4·0% compared with 3·7±2·1% for those dosed via the rumen.64Cu present in the whole plasma volume 20 h after dosing (y, % dose) was highly correlated with availability (x, %), the equation beingFour out of a group of eight milk-fed lambs were given access to a proprietary concentrate from birth and milk intake was progressively restricted so that by 15–21 days they were wholly dependent on the concentrate. Mean Cu availability at 23 days was 8·3±3·4% compared with 75·0±5·4% for lambs continuing to receive milk substitute alone. The corresponding values for 64Cu in plasma were 0·34±0·03 and 1·41±0·14% dose.Less than 1·1% of the 103Ru and 64Cu doses were excreted in the urine after 48 h and no 103Ru was detected in the plasma.The nutritional significance of and mechanisms for the reductions in Cu availability with age and weaning are discussed and methods for measuring Cu availability compared.