by feeding 500 – 700 mg/kg dietary Cu is alleviated by feed- ing extra DL-methionine. When pharmacological levels of copper are used in broiler production, it is common practice to add extra methionine.

Impact on cholesterol meta bolism Moderately high levels of diet Cu seem to have a consistent effect on reducing egg cholesterol content. Feeding 125 – 250 ppm of copper has been reported to reduce egg choles- terol by up to 25%. Unfortunately, the changes to yolk forma- tion means loss in egg production, often by a comparable 25%. The only consistent result from studies using copper to affect egg cholesterol, is that >95% of the additional copper ends up in the manure. Tissue cholesterol of meat birds is also reduced when birds are fed 250 ppm Cu.

To reduce Cu levels in ma- nure, there needs to be an evaluation of Cu bioavailability in the major feed ingredients, such as soy, wheat and maize.

the digesta. While Cu-deficient chicks have a drastically re- duced growth rate, their aortas can be double the normal size.

Toxicity Toxicity occurs when dietary levels approach 100 x normal. Initially, accumulation occurs in the liver, but after these levels reach 20 – 25 x normal, then Cu is released into the cir- culation, leading to destruction of red blood cells. No major feed ingredients are sufficiently high in Cu to cause toxicity. Toxicity has also been implicated in proventriculitis and giz- zard erosion, together with black discolouration of the ma- nure. Birds with sub-clinical cocci seem more prone to such gizzard erosion. Researchers suggest that the condition is al- most always seen in experimentally caged broilers, but less so in floor reared birds, suggesting some protection with diet fibre/litter eating. Other reports suggest that such Cu-in- duced gizzard erosion can be partially resolved by adding ex- tra selenium to the diet. There is little information available on any negative effect of high doses of copper on the activity of live probiotics.

Mineral interactions Interaction between copper and zinc, iron and molybdenum are often described as classical examples of mineral interac- tions. A large proportion of copper is absorbed from the duo- denum. Because zinc also binds aggressively to the same mu- cosal carrier, high levels of dietary zinc cause competition, leading to copper deficiency, although this is hard to diag- nose, since the diet contains normal levels of copper. The commercial practice of using pharmacological levels of diet Cu for growth promotion in meat birds has been questioned in terms of compatibility with phytase enzymes. High levels of dietary Cu result in reduced solubility of phytic acid, which may impact enzyme activity. There has been some controver- sy regarding the impact of high levels of Cu on requirements for certain amino acids. The growth rate of chicks depressed

Copper as an antibacterial High levels of copper are still used as a growth promoter, at 200 – 250 mg/kg diet, although the accumulation of copper in manure is leading to legislative restrictions. The manure colour of the bird changes markedly, and it is presumed that there will be some changes to the gut microflora. In turkeys, high levels of diet Cu cause greater evacuation of faecal droppings that have higher viscosity and contain up to 12,000 ppm of Cu. It has been suggested that the beneficial effect of feeding pharmacological levels of Cu may result from 10-15% improved digestion of haemicellulose. The best results from feeding high levels of Cu seem to occur after two to three flocks have been grown on re-used litter, implying the altered microbial status of the litter. When much in excess of 50 ppm copper is fed, most of the mineral will end up in the manure. There is no doubt that manure as a fertiliser from birds fed high levels of Cu increases the soil Cu. However, cal- culation of levels of soil and crop accumulation suggest that it takes many years to approach EPA “saturation” levels, and so the main current concern is “run-off” from soil into water- sheds. On the other hand, high levels of manure Cu suppress microbial uricase activity, limiting ammonia release.

Conclusions The minimum dietary requirements for Cu for poultry are around 5 – 8 ppm. Success with low levels of supplemental Cu (2-3 ppm) seem predicated on proportional reduction of all trace minerals and not Cu in isolation. When lower levels of Cu are considered as a means of reducing environmental pol- lution, then the bioavailability of Cu in conventional diet ingredients needs to be considered. If there is a need to reduce Cu levels in manure, then there needs to be an evaluation of Cu bioavailability in the six to eight major feed ingredients used worldwide. Often >90% of Cu consumed will appear in the manure, where soil accumu- lation is less problematic than the potential leaching of Cu into watercourses.

▶ ALL ABOUT FEED | Volume 29, No. 5/6, 2021 17


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