Studies in mineral metabolism. XXXIII. Iodine in the nutrition of sheep. Second report

Abstract

1. Data are presented on the effect of KI in the feed of 40 merino ewes for a period of 30 months. 2. The quantities of KI given per sheep daily were 0.002 grm., 0.02 grm., 0.06 grm. in three groups respectively, while one group received no KI and acted as controls. 3. Observations were made on the food consumption, weight increase, wool production, reproduction and health of the animals for the full period of the experiment. Further, observations were made on the oestrus cycle of the ewes and no significant group differences were observed. 4. The animals were fed in individual feeding boxes except the hay, which was given ad lib. 5. It is concluded that neither the small dose nor the bigger quantities of KI fed had any visible effect on the weights, wool production and reproduction of the animals. 6. It is also pointed out that the ill effects ascribed to iodide feeding in the earlier work were apparently aggravated by another deficiency, the possibility of the existence of which was not considered in the earlier work, viz. vitamin A. 7. It is concluded that the addition of KI to sheep licks is unwarranted, may even produce visibly detrimental effects under conditions of drought, when a vitamin A shortage may exist, and is to be discouraged in practical farming unless there is reason for believing that an iodine deficiency exists. 8. Further work on the effects of iodine feeding under practical conditions, as for instance during severe droughts when apparently detrimental effects may be experienced, is being undertaken. The writers wish to acknowledge gratefully the assistance of Mr. A. P. Malan, Statistician, in dealing with the results given in the lambing charts.