The distribution of four trace elements (Fe, Mn, Cu, Zn) in forage and the relation to scrapie in Iceland

BACKGROUND: Previous studies indicated that the iron (Fe)/manganese (Mn) ratio in forage of sheep was significantly higher on scrapie-afflicted farms than on farms in other scrapie categories. This study was conducted to examine whether Fe and Mn in forage of sheep varied in general according to the scrapie status of different areas in the country. Copper (Cu) and zinc (Zn) were also included because of a possible relation to scrapie. METHODS: The country was subdivided into seven Areas (I-VII). Three Areas (I, IV, VII) were designated scrapie-free (never diagnosed or eradicated) and three as scrapie-endemic (II, III, VI); status of Area V was taken as unsettled. Of the harvest 2007 1552 samples were analysed from 344 farms all over the country, mostly grass silage from plastic bales (>90%) and from the first cut (70% or more). Results were expressed as mg kg(-1 )dry matter. RESULTS: Fe varied enormously from less than 100 mg kg(-1 )to 5000 mg kg(-1). Mn varied nearly thirtyfold (17-470 mg kg(-1)). Fe concentration was significantly lower in Area I than in Areas II, V and VI. Mn concentration was significantly higher in Areas I, IV and VII than in Areas II, III, V and VI. The Fe/Mn ratio was significantly less in Area I than in the other areas (except Area IV). Mean Cu concentration was 6.6-8.3 mg kg(-1 )and the mean Zn concentration was 24-29 mg kg(-1). They differed significantly in some areas. CONCLUSIONS: 1) Fe tended to be in lower amounts in sheep forage in scrapie-free than in endemic areas; 2) Mn was in higher amounts in forage in scrapie-free than endemic areas; 3) the Fe/Mn ratio was lower in scrapie-free than in endemic areas; 4) the Fe/Mn ratio may possibly be used as an indicator of scrapie status; 5) Cu and Zn in sheep forage were not related to scrapie; 6) further study on the role of Fe and Mn in the occurrence of scrapie in Iceland is needed.