Copper in Ruminants: Beware of Going from Deficiency to Toxicity


By V. Kromm and D. Cardoso, Animine


COPPER FOR RUMINANTS It has long been recognized that copper (Cu) is an essential trace element in ruminants. As copper is required in many key enzymes, any sub-clinical deficiency will impair animal health, fertility and production performance. Copper requirements and maximum copper levels authorized


in the European Union are presented in Table 1. For bovine, the requirements are around 10 mg/kg DM with higher values (up to 18 mg/kg DM) for dairy cows in the close-up period and in the first weeks after parturition. Higher values are recommended for caprine (up to 25 mg/kg DM) but lower for ovine (up to 10 mg/kg DM) which are highly sensitive to excess copper. A genetic variation observed in copper absorption can also influence copper requirements. Literature mentions in particular higher requirements in Scottish Blackface than in Texel sheep and in Jersey than in Holstein Friesians cows. After the 2016 EFSA opinion on the revision of maximum contents


of dietary copper, the maximum EU copper level authorized in bovine feed recently decreased from 35 to 30 ppm while it increased from 25 to 35 ppm for caprine (Regulation (EU) 2018/1039). In ruminants, copper is not used at growth promoting dosages like it


is in the case of monogastric diets. Thus, the re-evaluation of maximum copper levels is not only driven by environmental concerns but also by nutritional objectives. Poultry and pigs have copper requirements well established for decades; in ruminants - and especially bovine, more research is still needed. It is due to the high sensitivity of ruminants to copper with a small margin between deficiency and toxicity, but also to the presence of antagonists in the rumen which can decrease the availability of copper for the animal.


RISK OF SECONDARY DEFICIENCIES Copper deficiency is occasionally observed in ruminants. Mineral deprivation occurs due to either a primary or a secondary deficiency.


The primary deficiency is the “classic” form, in which low levels of copper are supplied in the diet and do not meet animal requirements for this mineral. This scenario is most unlikely to happen, because the main ingredients of the diet meet the animal needs for copper, as shown in Table 2. On top of the basal diet, mineral feeds are usually added in order to secure a large safety margin.


Table 2: Cu concentration in some feedstuffs used in dairy cow diets


Ingredients Grass silage Corn silage Beet pulp Sorghum


Soybean meal Sunflower


Rapeseed meal


Cu mg/kg 8-10 4 9 4


14


20-30 7


Secondary deficiency happens when, even at proper level of


copper supplementation, the presence of other dietary factors interferes with mineral absorption and metabolism. This phenomenon is the main cause of copper deficiency in ruminants. Sulfur (S), molybdenum (Mo) and iron (Fe) are the most important dietary factors to negatively impact copper absorption. In the rumen, molybdenum and sulfur interact, forming complexes


called thiomolybdates (TM). The nomenclature follows the level of sulfur chelation: mono (TM-1), di (TM-2), tri (TM-3) or tetra (TM-4) -thiomolybdate. Figure 1 illustrates how these metals interact in the rumen; TM-1 and TM-2 are less stable bonds and most likely reversible in the acidic environment of the abomasum, as TM-3 and TM-4 are more stable and with a greater affinity for copper. The ionic form of copper, once released in the rumen environment,


Table 1: Cu requirements and maximum Cu dietary level authorized in the EU for ruminants (mg/kg complete feed)


Bovines before the start of rumination


Requirements


NRC, USA (2000, 2001, 2007) GfE, DE (1995, 2001, 2003) CVB, NL (2005)


Agroscope, CH (2006, 2009) INRA, FR (2018)


Maximum Cu dietary levels authorized 1 1 Regulation (EU) 2018/1039


PAGE 40 SEPTEMBER/OCTOBER 2020 FEED COMPOUNDER


10 -


10 6 -


15 Other bovines


Beef 10


8-10


11-13 10


10 30


Dairy 11-18 10


7-17 10-15 Small ruminants


Ovines 4-8 -


6-7 5


10 15


Caprines 15-25 10-15 8 8


15-25 35


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