ISSUE FOCUS 34 FEED & ADDITIVE MAGAZINE March 2022 growing number of countries in Europe, America and Oceania, an increased concentration of Cu in the liver of dairy cow herds over the years. A study carried out at the University of Nottingham (UK), showed that most sheep (60%) have normal liver Cu and are more likely to be deficient. The same study showed that 70% of dairy cattle in the UK have high Cu status (Figure 2) with 60% of the farms feeding animals with Cu levels above 20 mg/kg DM and 8% above the legal limit. The main reasons reported were misinformation of farmers and the fear of deficiency. In addition, the multichannel supply of trace elements (via concentrates, mineral feeds, nutritional supplements…) and the variability in forages composition make it difficult to monitor total Cu supplementation. CHRONIC COPPER TOXICITY Prolonged Cu intake, above requirements, can lead to chronic toxicity which is the result of the slow accumulation of Cu in the liver during a long period of time. At the opposite of acute toxicity, Chronic Copper Poisoning can remain ‘silent’ for months or years, before the toxicity is apparent. The elevation of liver enzymes in the blood, that indicates hepatopathy caused by high levels of Cu, can be related to a wide range of other diseases. Additionally, clinical signs are mild and with low morbidity which can often be overseen by veterinarians. Increase in blood Cu is only seen as a second stage when the liver is overloaded and Cu 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 Cu status and amplify the awareness of farmers for Cu toxicity. Recent research indicates that Cu already accumulates in bovine liver at dietary levels recommended by the industry, and that cattle could be less tolerant to Cu than previously thought. CONCLUSION This topic highlights the importance of precision mineral feeding in order to guarantee an efficient supply of Cu, safe for the animal and for the environment. Cu 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 Cu needed to meet the animal requirements, without forgetting drinking water which can be a significant source of iron and sulfur for the animal. The choice of the source of copper supplemented in the feed is also of importance. Indeed, Cu 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. Monovalent copper oxide, combines high bioavailability with a low solubility at rumen pH. This innovative source of Cu will help to restrict the need for higher Cu dosages in ruminant diets and to preserve animal productivity, health and welfare. Figure 2 – Liver Cu status of dairy cow in the UK (µmol/kg DM) (University of Nottingham) (Image courtesy by Dr. Clarkson)
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