The status of essential elements and associations with milk yield and the occurrence of mastitis in organic and conventional dairy herds

• No studies have been carried out on the major essential elements in organic dairy cows.
• From January 2008 the diet of organic dairy herds has been 100% organic in the EU.
• Feed ration management is strictly more important in organic herds to avoid mineral imbalances.
• Essential elements׳ importance to combat clinical mastitis reinforces better feeding strategies.

There is a lack of detailed information on the impact of organic feeding regulation on the health and well-being of cows. This has become especially important since January 2008 when the EU required 100% organic ration for organic dairy herds. The aim of this investigation was to determine and compare the levels of essential elements in organic and conventional dairy herds, and to associate them with milk yield and the occurrence of mastitis. The field study was carried out in 10 organic and 10 conventional herds from 2005 to 2010. This period included the point in time when the ration became 100% organic in organic dairy herds. Essential element concentrations (Cu, Co, Se, Zn, Mn, Mo, I and Fe) were determined by inductively coupled plasma–mass spectrometry in 158 serum samples. Associations between concentrations of elements and milk yield and mastitis were determined with mixed linear and logistic regression models, respectively. No significant differences in metal levels between organic and conventional herds were found. No severely deficient concentrations of essential elements were observed in organic herds, either before or after the change in regulation. Cows with low serum concentrations of Se had lower somatic cell counts. Daily milk yield was significantly influenced by deficient concentrations of Cu. For the evaluation of clinical mastitis occurrence, herds were classified for each element, based on the individual values of the sampled cows. Low levels of some elements (Se, I) were associated with a reduced risk of mastitis occurrence. However, other elements indicated a protective effect against mastitis.