Overfeeding minerals

Published 13 September 13

Majority of British dairy farms are overfeeding minerals

Most farms are feeding well above recommended levels of minerals, increasing diet costs and in some cases, possibly having an impact on animal health and a negative effect on the environment, according to Professor Liam Sinclair from Harper Adam University.

Professor Sinclair, who is working on a DairyCo-funded research programme examining mineral requirements of dairy cow, looked at mineral levels fed on 50 farms and compared them with the recommended requirement levels. The project took samples of TMR, concentrate, forage and water minerals as well as from additional sources such as boluses, injections and free access. The results can be seen in graph 1.

Copper

Under normal circumstances, total copper in the ration should typically be 20mg/Kg DM. But of the 50 farms in the study, 31 were feeding above this level and four were feeding above the maximum permitted level of 40mg/kg DM.

Copper is deposited in the cow’s liver until the burden becomes too great and it is released into the bloodstream, possibly causing death by toxicity. Because the copper is stored in the liver, a blood test will not help identify high copper levels. Liver biopsies are a more accurate test but can be expensive.

Copper deficiency is also the most common mineral issue seen at the Vet Investigation Centres but most of the deficiency problems in the UK are due to the effects of antagonists such as molybdenum, sulphur and iron. Some of the farms in this study had high molybdenum levels but these were not the same ones that were feeding high levels of copper.

Steps can be taken to help avoid overfeeding minerals:

  • One person on the farm should have responsibility for mineral nutrition, taking into account all the different sources
  • Assessing mineral requirements on farm should start with forage analysis
  • Forage analysis is more useful than blood test when looking at copper levels
  • Biopsies of cull cow livers can also help identify if there is excess copper in the diet.

The DairyCo Research Day brought farmers information about eight DairyCo funded projects. Information about some of these projects will be in future issues of Forage for Knowledge.