Copper in dairy rations: Is too much as bad as too little?

Evaluating copper levels in every feed source and supplement before formulating rations for dairy cows – and youngstock – will help meet animal requirements but prevent overfeeding and protect animal health.

Copper is an important trace element for cows and heifers, and no single source will cause copper toxicity.

But added together, a range of feeds and supplements containing copper can produce an excess in the diet.

See also: Excess copper found to impair liver function in heifers

Studies at Harper Adams University (see “Research into overfeeding of copper to heifers”) have shown that feeding high levels of copper to replacement heifers results in better growth rates and earlier oestrus.

Yet longer term, these animals also had indicators of liver damage, poorer conception rates, greater body tissue mobilisation, and negative energy balance – particularly in early lactation.

Harper Adams researcher Prof Liam Sinclair says: “We have shown that the liver is compromised and the immune function changed, and fertility reduced, through overfeeding copper.

“The problem is worse when diets result in a low rumen pH – such as high levels of concentrates in early lactation – as this increases copper availability.”

Prevent not test

He says his advice to prevent overfeeding – by assessing the copper content in everything that might be eaten by the calf, heifer or cow – is easier than trying to check a herd’s copper status through testing.

Blood samples are unreliable indicators of body copper reserves, as results can be influenced by the animal’s immune system.

Liver biopsies are the best way to test, but taking them from lactating dairy cows is invasive, and analysing those from cull cows may not be representative of the herd because there is probably an underlying health reason for their exit.

“The best starting point is to look at the mineral content of forages and every feed,” Liam explains.

“It is a legal requirement to state copper levels in feed, so it should be possible to calculate how much is being fed and compare this with actual animal requirements.”

Prof Liam Sinclair © MAG/Shirley

Accounting for all sources of minerals, he includes blocks, boluses, buckets, licks, powders, injections and the water supply.

“Grazed grass, silage, cake, blend – even soil,” he says. “Cows can eat 0.75kg of soil dry matter a day from grazing wet pastures and roots, yet no one looks at soil availability of copper.”

Anecdotally, Liam thinks the dairy industry is overfeeding copper to youngstock as a result of a strong focus on copper deficiency and its consequences.

Minerals research for the past 50 years has focused on what happens to cows lacking copper, so the temptation is always to think that more is better, he says.

Copper balance

However, he points out that copper has a narrow window where underfeeding tips into overfeeding.

“Amounts below 10mg/kg dry matter a day are potentially deficient but need to be considered with sulphur and molybdenum; they are common antagonists that can lock up copper and prevent its absorption by the cow,” he explains.

“When feeding more than 20mg, copper could be accumulating in the liver, depending on these antagonistic minerals, while rates of 30mg are at high risk of toxicity.”

Overfeeding not only arises when failing to account for supplements, but also when offering free-access minerals (particularly if molasses is used to improve palatability).

This is because determining actual mineral intakes is “hit-and-miss”, Liam says.

“Cows don’t always stop eating them. Research shows that some cows may eat little, or none, and some over-consume, but this can be erratic day by day.”

Another unaccounted source of potentially high levels of copper is the practice of giving cows’ total mixed ration refusals to calves and heifers.

Nutrition software

As herd sizes have grown, farm owners have outsourced their nutritional advice, operating a team approach that includes vet and nutritionist in management decisions, with a key business driver to buy feeds cost effectively.

In such cases, Liam says the reliance on rationing programs will only flag up underfeeding of copper, not overfeeding.

“The focus is on metabolisable energy, protein content, fibre and cost. Minerals and vitamins are often last and do not get the attention they should get.

“But now, with a focus on cow health relating to excess copper, software should also look at overfeeding.”

© Tim Scrivener

He has updated his training for the feed industry via the post-graduate nutrition diploma he runs at Harper Adams.

Yet the UK has not officially reviewed its mineral guidelines since the Agricultural and Food Research Council in 1991.

Instead, the feed industry is following 2021 US recommendations through the National Academies of Science, Engineering and Medicine.

Liam thinks mineral advice to farmers continues to be “bamboozling”, and that farmers need to trust their specialists to be aware of all the different interactions and risks associated with underfeeding and overfeeding.

“There is greater awareness now about overfeeding minerals, but farmers need to ask the question, particularly about copper, nitrogen and phosphorus: can I feed less, and still meet requirements, and what are the effects going to be?”