DEATH CASES: THE TIP OF THE ICEBERG While in the past, copper deficiencies used to occur in grazing ruminants, researchers have observed in a growing number of countries in Europe, America and Oceania, an increased concentration of copper in the liver of dairy cow herds over the years. Indeed, surveys in the USA, New Zealand, UK and The Netherlands
reported that liver copper was above critical thresholds in a large number of animal and that this tendency was increasing when herds was monitored over the years (Figure 3) The main reasons reported for this increase were misinformation of
farmers and the fear of deficiency. The concept of “the more the better”, in which recommendation limits are seen as targets to be achieved, is more and more accepted among farmers. In addition, the multichannel supply of trace elements (via concentrates, mineral feeds, nutritional supplements…) makes it difficult to assess the total copper in the diet and increases the risk of oversupply. This increase in total copper supplemented can have a negative
impact on animal welfare with cases of chronic toxicity more and more identified. At the opposite side of the scale to acute toxicity, which occurs
after the accidental ingestion of a big quantity of copper, Chronic Copper Poisoning (CCP) is the result of the slow accumulation in the liver of smaller quantities of copper during a long period of time. Identifying CCP is not an easy task in the first stage as there is no change in blood copper and the identification of the problem can only be done by evaluating copper liver concentrations. The elevation of liver enzymes in the blood, that indicates
hepatopathy caused by high levels of copper, can be related to a wide range of other diseases. Additionally, clinical signs are mild and with low morbidity which can often be overlooked by veterinarians. Increase in blood copper is only seen as a second stage when the
liver is overloaded and copper is released into the bloodstream. This causes acute toxicity with animals often dying within 24-48h.
A growing number of lethal cases reported by veterinarians showed
that such silent intoxication is spreading in dairy herds, which urges the development of strategies to monitor herd copper status and amplify the awareness of farmers for copper toxicity. Recent research indicates that copper already accumulates in
bovine liver at dietary levels recommended by the industry, and that cattle could be less tolerant to copper than previously thought.
CONCLUSION The risk of secondary copper deficiencies in ruminants, and in general the increasing attention now being paid to trace minerals deficiencies, resulted over the last years in an increase in the quantity of copper supplemented in bovine diets. The usage of theoretically more bioavailable sources, such as chelates, did not reverse this trend. Because chronic copper toxicity is difficult to diagnose before the final stage where irreversible effects occur up to death, copper supplementation should be driven by the objective to prevent hepatic toxicity and oxidative damage. Copper bioavailability for ruminants is mainly determined by sulfur,
molybdenum and iron levels in the diet. Thus, complete forage analyses are essential to fine tune the quantity of copper needed to meet the animal requirements, without forgetting drinking water which can be a significant source of iron and sulfur for the animal. More advanced analytical techniques will be required to understand the effects of the chemical form of these antagonists. The choice of the source of copper supplemented in the feed is
also of importance. Indeed, copper sources with known physicochemical characteristics and dissolution kinetics can help to select the one which is the less susceptible to form complexes in the rumen. Copper(I) oxide (CoRouge®
), recently authorized in the market, combines high
bioavailability with a low solubility at rumen pH. This innovative source of copper will help to restrict the need for higher copper dosages in ruminant diets and to preserve animal productivity, health and welfare.
Figure 3: Evolution of copper concentration in cattle liver over the last two decades (Grace and Knowles, 2015; Counotte et al., 2019)
1000 1500 2000 2500 3000
500 0
Median of copper loading in New Zealand cattle liver Number of cases of Dairy cows with Cu liver above 600 mg/kg DM in The Netherlands
PAGE 42 SEPTEMBER/OCTOBER 2020 FEED COMPOUNDER
0 2 4 6 8 10 12 14 16 18
Copper in liver (mg/kg DM)
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
Number of cases
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