Effects of iodine supplementation on the productivity of Romney ewes in the Wairarapa region of New Zealand

Abstract

The objective of this study was to examine the effects of iodine supplementation of ewes on their plasma thyroid hormone concentrations and production of ewes and their lambs. The study was conducted in the Wairarapa, a region where apparent subclinical iodine eficiency has been reported. Two groups of 200 Romney ewes, one of which was injected with iodised oil (Lipiodol}®) 3 weeks before mating, were monitored for 1 year from mating. Thyroxine concentrations were significantly (P < 0.0 1) elevated in the iodine-supplemented ewes 113 days after treatment. Supplemented ewes were heavier at mating (P < 0.05) but did not differ significantly from controls in lambing performance, lamb growth rate, or ewe fleece production. Lipiodol® was shown to be an effective means of supplementing ewes with iodine, but untreated ewes apparently obtained adequate levels of iodine from plant and soil material ingested. High soil intakes associated with intensive winter rotational grazing are likely to have been responsible for adequate iodine intakes in control ewes.

Keywords:

• iodine
• thyroid hormones
• sheep performance
• grazing systems