SUBCLINICAL SELENIUM INSUFFICIENCY .3. THE SELENIUM STATUS AND PRODUCTIVITY OF LAMBS BORN TO EWES SUPPLEMENTED WITH SELENIUM

Measurements were made of blood selenium (Se) concentrations and liveweights of Dorset Horn X (Border Leicester X Merino) and Merino lambs born in October to ewes which were supplemented or not supplemented with intra-ruminal Se pellets and grazed at 6.3 or 12.5 ewe/ha for 4 consecutive years. Lambs were not supplemented with Se and most observations were made between birth and weaning. In some years the Merino lambs were grazed as a single flock for a further 18 months after weaning, and liveweights and fleece characters were recorded at 10 and 22 months of age. Blood Se concentrations of lambs at birth varied with the Se treatment of their dams but were generally lower in the lamb and declined during lactation. In lambs born to unsupplemented ewes, concentrations were lower at the high stocking rate, and declined with increasing rainfall in the preceding January-June period. Selenium concentrations were reduced in twins and this was particularly evident in lambs born to supplemented ewes. Liveweights at birth, in mid-lactation and at weaning were significantly increased in lambs born to Se-supplemented and crossbred ewes, and in lambs born as singletons. The response in liveweight following Se supplementation was greater in lambs reared at the high than at the low stocking rate, and in Merino than in crossbred lambs. The response to Se supplementation was correlated with rainfall during the preceding February to July, and was greater in early lactation. Clean fleece weight at 10 months of age was increased by 9.5% and fibre diameter by 0.3-mu-m in lambs born to ewes which had received supplementary Se. Differences in fleece weight were not detected at 22 months.