be around 80% while values are closer to 40% for SBM. These lower levels may be due to greater binding of Cu with phytate, and so availability may be higher when using phytase. Copper sulphate and copper oxide have been tradi- tional sources of supplemental copper, and although bio- availability values depend on numerous factors, both sources average around 65 – 75%. Tribasic copper chloride (TBCC) is now often used commercially as it has no issues with hygroscopicity. There is also considerable interest in the testing efficacy of products loosely termed “organic copper”, which are usually combined with amino acids or proteins. It is often claimed that these minerals are preferentially absorbed and metabo- lised and provide less opportunity for interference with other minerals. There have been reports of very low levels of these organic minerals being adequate for poultry with a view to reducing mineral excreta output.

Copper deficiency Copper deficiency results in anaemia, growth depression, bone disorders, depigmentation of feathers and diarrhoea. Young chicks will become lame in two to four weeks when fed a copper-deficient diet. Bones are fragile and easily broken


and this is unfortunately often indistinguishable from Vitamin A deficiency. Iron deficiency, resulting in a comparable anae- mia, fails to produce similar bone changes. With deficiency, the cartilage is found to contain more free lysine, which under normal conditions binds to form important cartilage structures. The metabolic activity of this abnormal cartilage resembles that seen in situations of tibial dyschondroplasia. Both copper and iron deficiencies have been reported to result in loss of feather pigmentation in colored chickens and bronze turkeys. Poults are especially susceptible, exhibiting depigmentation within 10d of feeding a Cu-deficient diet. Chicks hatched from copper-deficient hens lack critical en- zymes in the aorta and liver. The heart problem seems similar to the mechanism involved in abnormal cartilage formation, so the aorta becomes inflexible. In turkeys this can lead to symptoms similar to “aortic rupture”. Again, there are diagnos- tically high levels of free lysine in the affected aorta. In field cases of naturally occurring aortic rupture, many birds have <10 ppm Cu in the liver, compared to the 15 – 30 ppm that is found normally. A high incidence of aortic rupture has been seen in turkeys fed 3-nitro, although this problem could be re- solved by feeding higher levels of copper, suggesting that products such as 3-nito may simply combine with copper in

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

The copper pro- portion that is available to the bird is variable due to farming conditions and the prior nutri- tional status of animal proteins.

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