We need to be smarter with our assessment of mineral advice (especially trace minerals) and more efficient at supplementing.

All animals require minerals to support life, but we need to decide how much they need. Every mineral has an adequate threshold, above which giving more will not produce a production response.

So why are we still seeing advice that we need to have serum selenium levels at least three times the adequate level to prevent RFM? It is just wrong. A veterinary report I read stated ‘We like to see levels around 600nmol/L for optimal performance, although levels ranging down to 140nmol/L are considered adequate to maintain cow health.’ “Optimal” is misleading here. A cow will perform just as well at 150 as it will at 600, and you will have saved money on unnecessary supplementation.

1.  Selenium

Ravensdown commissioned a study on selenium levels and the resulting paper has been published in a world-respected journal as well as presented to our dairy vets at their national conference. This study found no production or health benefits from supplementing with higher levels of selenium in cows that were adequate.

Furthermore, the main effect of supplementation of cows with low selenium was on milk production, not reproduction, and there was no association with retained foetal membranes (RFM).

2. Copper

Copper (Cu) is stored in the liver and high levels can be toxic – cows have died with liver levels of 2300-2400mol/kg. The liver can store a lot of copper.

If copper supplementation stops in a cow with a liver copper above 400 it has copper reserves sufficient for about six months; if liver copper is greater than 1000, those reserves are likely to be sufficient for more than a year (See Fig 1).

So why is the advice given to continue copper supplementation when liver copper levels are far higher than the 95 threshold? Farmers may be heeding the wrong advice as a survey carried out in the Waikato showed six out of ten farms had a mean concentration of copper in liver greater than 1,200mol/kg fresh tissue.

The problem is not with the supplements per se, excepting that there is virtually no evidence that “organic” trace elements offer any advantage over the cheaper “inorganic” elements, it is that the market, influenced by nutritionists with a product to sell, is faulty.