The Society of Feed Technologists had its annual (virtual) conference on Thursday, April 22, with a series of 6 very interesting and topical presentations by eminent speakers. Professor Liam Sinclair from Harper Adams spoke about copper metabolism and the current research his group is doing.
Copper is the commonest trace element deficiency, either primary (lack of copper in the diet) or, more commonly, secondary, due to other elements (especially molybdenum and sulphur) interfering with copper uptake. However, copper is also the most widely reported trace element toxicity, which can cause death of cattle (and sheep). How does this happen?
Since it is the commonest trace element deficiency, copper is often routinely supplemented to dairy cows by a variety of routes, including in feed, water, boluses and others. The recommended feeding level is 11-15 mg copper/kg feed dry matter, with a recommended maximum inclusion rate of 20 mg/kg in the UK and a EU limit of 34mg/kg. Sinclair and Atkins (2014) surveyed commercial UK dairy farms and found a mean copper intake (from all sources) of 28 mg/kg in early lactation cows, well above the recommended maximum. In early lactation, 80% of the herds fed copper at more than 20 mg/kg and 20% at greater than 34 mg/kg. In an attempt to avoid the adverse effects of copper deficiency, farms were often feeding too much copper. When this happens, copper accumulates in the liver and kidneys, until a level can be reached where animals suffer a ‘haemolytic crisis’, a sudden onset destruction of the red blood cells – usually resulting in the animal being found dead.
Does excess copper affect health and productivity before it (potentially) causes sudden death? Professor Sinclair’s research at Harper Adams followed two groups of heifers from 4 months of age to 100 days after their first calving. They were fed different levels of copper; one group was fed a ‘normal’ 15 mg/kg, and the other was fed 27 mg/kg (a similar level to the study above). Perhaps unsurprisingly, the second group had higher liver copper levels throughout the study. During the rearing period, the high copper group had greater liveweight and BCS gains and earlier first heat, but also demonstrated reduced conception rates. After calving, both groups had similar feed dry matter intakes. However, the group, which was fed more copper, lost more BCS and gave less milk – this high copper group had evidence of increased liver damage (in addition to increased copper accumulation in the liver) and higher post-calving BHB values. Therefore, it seems that feeding excessive copper is not only wasteful (economically) and increases the risk of animals dying, but also has a detrimental effect on performance.
In addition, they observed that, although daily copper intakes were the same throughout the study, copper accumulated in the liver at a greater rate from pre-calving until 100 days post-calving. Why did this happen? They thought that it could be an effect of low rumen pH in the post-calving period. They tested this theory by feeding copper at 15 mg/kg to two groups of early lactation cows – one group fed a 15% starch ration and the other a 22.5% starch ration. Each group was then further divided into two – with half receiving additional molybdenum and sulphur (to interfere with copper uptake) and half not. Using rumen pH boluses, as expected, they saw that the high starch group had lower rumen pH throughout the day. Higher starch/lower rumen pH resulted in more copper accumulation in the liver. Also, the animals fed additional molybdenum and sulphur had reduced feed dry matter intakes – this effect was greater in the high starch/low rumen pH animals. Professor Sinclair’s theory is that at lower rumen pH, more sulphur in the ration is converted to hydrogen sulphide gas. This has two effects: (i) less sulphur is available to bind to copper, so more copper is absorbed and (ii) some of the hydrogen sulphide is inhaled, gets in the bloodstream to the brain, where it has several effects (polioencephalomalacia), including reducing feed intakes.
The overall conclusions from Professor Sinclair’s copper presentation were: