Minerals have traditionally been supplemented to cattle to rectify deficiencies that may be present in forages and supplementary feeds to ensure optimal performance and health. In a recent survey of winter mineral feeding levels to dairy cows in the UK, Sinclair and Atkins (2015) reported that most minerals were being fed at levels well above requirements, with organic herds supplementing at a similar level to non-organic herds.
In support of this, Kendall et al., (2015) reported that approximately 40% of cull dairy cattle and 17% of cull beef cattle had liver copper concentrations above the recommended maximum limit. Over-supplementing minerals not only increases diet cost, but can have a negative environmental impact (e.g. phosphorus), interfere with the absorption and metabolism of other minerals, and for copper in particular, be toxic.
Reasons for over-supplementation are varied, but undoubtedly many farmers wish to avoid signs of deficiency, which are widely reported, particularly in high forage or extensive grazing systems. To reduce these issues, mineral feeding levels should be based on national recommended feeding levels, include a forage analysis, take account of all sources (e.g. water, free access minerals, boluses), and have one person on the farm who has overall responsibility.