Iron loading and secondary multi-trace element deficiency in a dairy herd fed silage grass grown on land fertilized with sewage sludge
Recycling sewage sludge by applying it to agricultural land is strategically important in the European Union and is regulated by Directive 86/278/EEC, aimed at protecting the soil and humans from the presence of unwanted substances. However, because of the ruminant feeding habits, there is a risk that animals grazed on pasture or fed crops grown on land treated in this way may ingest biosolids adhered to foliage and/or on the top soil. This paper describes an episode of toxicity in a dairy herd consuming silage from a field fertilized with sewage sludge produced in a wastewater treatment plant. The affected cows were recumbent, unable to rise and suffered diarrhoea. Analysis of tissues (fresh weight) from a cow that subsequently died revealed severe hepatic iron loading (6720 mg/kg) and secondary multi-trace element hepatic deficiency, particularly of copper (0.812 mg/kg) and manganese (0.436 mg/kg), but also selenium (0.164 mg/kg) and zinc (19.9 mg/kg). The study findings indicate that the use of sewage sludge in agriculture can cause secondary multi-trace element deficiencies in ruminants. Careful attention should be taken when crops are ensilaged avoiding top-soil sewage sludge contamination, since the acidification process may greatly increase Fe bioavailability.
KeywordsTrace elements Sewage sludge Iron Copper deficiency Cattle Fertilizer
AHHM is grateful to Conselho Nacional de Desenvolvimento Científico e Tecnológico, CNPq, for his research productivity fellowship. The authors thank Lucia Casanova Iglesias and staff of RIAIDT for their technical assistance. The English grammar of the text was revised by Christine Francis.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Compliance with ethical standards
Ethics approval and consent to participate
All procedures and animal handling followed the ethical principles in animal experimentation.
The authors declare that they have no competing interests.
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