Intake of selected minerals on commercial dairy herds in central and northern England in comparison with requirements

Overfeeding minerals to dairy herds will raise diet cost, increase their excretion into the environment and for minerals such as copper (Cu) can lead to poisoning and cow death. In contrast, underfeeding may compromise cow performance, health and fertility. Despite this, the level of mineral intake on commercial dairy units is poorly documented. To determine the mineral intake on commercial dairy herds in central and northern England over the winter of 2011/12 and compare these to recommended levels, samples of compound feed, forage mix, supplementary sources (including lick blocks, rumen boluses, free access minerals and drenches) and drinking water were collected from 50 herds over the winter feeding period and analysed for 10 macro and trace minerals. For cows in early lactation the mean dietary concentration of phosphorus (P) was 4·5 g/kg dry matter (DM) (s.d. 0·70), 0·1 g/kg DM below UK requirements, and for calcium (Ca) was 10·2 g/kg DM (s.d. 2·94), 5·9 g/kg DM above requirements. Trace mineral concentrations were also in excess of requirements in early lactation, with a mean dietary Cu concentration of 28 mg/kg DM (s.d. 9·85), approximately 18 mg/kg DM above UK requirements, with 32 of the 50 herds feeding above the UK industry recommended maximum of 20 mg/kg DM and 6 above the EU limit of 40 mg/kg DM. Dietary mineral concentrations were generally lower in late lactation but still higher than requirements. The forage mix (including supplementary feeds and minerals) contributed the greatest amount of minerals, with percentile ranges (10th–90th) of 2·1–4·4 g/kg diet DM for P, 1·4–3·2 g/kg diet DM for magnesium (Mg) and 5·3–25·0 mg/kg diet DM for Cu. Compounds fed in the milking parlour supplied (10th–90th percentile) 0·0–1·4 g P g/kg diet DM, 0·0–1·2 g Mg/kg diet DM and 0·0–11·6 mg Cu/kg diet DM. For the upper 90th percentile of dairy herds, water supplied proportionally 0·08 of Ca requirements recommended in early lactation in the UK, whilst supplementary mineral sources supplied up to 0·64 of Cu and 0·43 of zinc (Zn) requirements. High dietary concentrations of Cu were not justified by the presence of the dietary antagonist molybdenum (Mo), with no relationship between the two minerals in early or late lactation diets. In conclusion, most dairy herds were feeding excess amounts of minerals over the winter feeding period when compared to UK or other national recommended guidelines, with the implications of a higher diet cost and negative impact on the environment and animal health.