Effects of iodine supplementation of pregnant and lactating ewes on the growth and maturation of their offspring

Abstract

Iodine supplementation (20 mg KI twice weekly) to ewes during the last month of pregnancy and the first 3 months of lactation increased productivity. Production traits enhanced by this treatment included the birth weight (3.9 vs 3.5 kg; P < 0.01), survival (84% vs 64 %), growth rate (P < 0.05), and mature SIP wool follicle ratio of lambs (1 4.9 ¦ 1.2 vs 10.3 ¦ 1.6). These differences were most apparent in animals receiving a low plane of nutrition (i.e. intake restricted to maintain ewe liveweight at approximately 32 kg). There were no marked changes in the body composition of lambs in the treated groups. The control animals in these studies exhibited only marginally depressed plasma thyroxine levels (4.7 ¦ 0.4 ¦g %). Iodine supplementation can be used to partly circumvent the low productivity of tropical Merinos receiving a low plane of nutrition. More marked benefits could probably arise from treating animals which normally demonstrate low plasma thyroxine levels.