The effects of fertiliser iodine application on herbage iodine concentration and animal blood levels

Abstract

Two experiments were conducted to evaluate surface applications of potassium iodide and potassium iodate as alternatives to direct treatment of ewes where iodine (I) deficiency may be a problem. In Experiment 1, the hypothesis that grazing of pasture which had been sprayed with a potassium iodide and oil mixture results in increased blood iodine (serum T₄) levels in ewes was tested over two years on five farms in Southland and West Otago, New Zealand. The results show that spraying elevated pasture I levels from March to pre lambing. The increased pasture I levels increased serum T₄ levels by only 1.5% in late winter, an increase which was not significant (P > 0.05). There were small increases in lambing percentages (1–5%) due to the spraying in both years, but these were not significant (P > 0.05).

In Experiment 2, the hypothesis that surface applications of potassium iodide and potassium iodate fertiliser can result in increased herbage I levels was tested on two farms in Southland and West Otago in 1996 and one farm in Central Otago in 1997. The trials ran from mid autumn (March/ April) to late winter (August/September) each year. There was a significant (P < 0.01) increase in pasture I levels after 6 weeks with both forms of iodine fertiliser, and this increase was still significant for the top application rates at the 19‐week measurement (P < 0.05 for Southland and West Otago, P < 0.01 for Central Otago). The iodide fertiliser was slightly more effective at increasing herbage I levels than was the iodate. However, despite the efficiency of I uptake being low (4.25% of the applied I taken up by the herbage), herbage I concentrations were lifted to acceptable levels and maintained at such for the duration of the study.

Keywords:

• iodine
• sheep
• pasture uptake
• surface application