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kittens exposed to galvanised iron door bars. Kittens which frequently rub against the galvanised iron bars, had a visible grey deposits of zinc in the fur around their whiskers. During grooming these kittens ingested high levels of zinc. Overconsumption of zinc was most probably the cause of the deficiency in copper, eventough there was an adequate copper level in the diet. Important for absorption of, for example, zinc, manganese and

copper are the mutual interactions as well as the dietary amounts of iron, calcium, phosphorus, potassium and sulphur and further antagonists. Unbalanced or high levels of some of these elements lead to shortages of the other elements. Other factors affecting the availability of trace elements are, for example, mycotoxins, crude fibre, tannins and phytic acid (Schenkel and Flachowsky 2002). As seen above, it is not always an imbalance in the diet which can lead to (secondary) deficiencies, also reduction in absorption capacity (e.g. age, genetics), environmental factors (e.g. galvanised iron bars) or supplementation by the dog owner (e.g. additional calcium supply to puppies) influence the health status related to trace mineral supply.

Inorganic, organic and hydroxy The various feed additives approved as trace element sources can be distinguished in terms of their availability for the animal and effect on other food components. The best known and largely used inorganic trace mineral sources are sulphates and oxides which vary mainly due to their solubility. The main task of trace mineral sources is to dissolve in the aqueous medium of the digestive tract and become available for absorption. A product with very low solubility, for example copper oxide, is demonstrated to have only very slight bioavailability and therefore it should not be used as a copper source in petfoods (NRC, 2006). The good solubility of sulphates should be an advantage for absorption, however, in aqueous environments sulphate minerals directly dissociate to sulphate and metal ions which react easily with other feed components. Already in the premix and production of food dissociated copper ions are known as strong pro-oxidant that initiate and speed up oxidation. Oxidation results in degradation and damage of sensitive ingredients such as vitamins or fats, as well as, forming harmful free radicals and peroxides thereby reducing palatability and shelf life of food (Miles et al., 1998; Lu et al., 2010; Pang and Applegate 2006; Shurson et al., 2011). In contrast to inorganic, organically bound trace elements (trace

element chelates) are stable in the diet and absorption by the animal is improved due to their chemical structure. Chelates are less soluble than sulphates, but have superior bioavailability compared to inorganic forms. This may be explained by less interactions with other food nutrients in the digestive tract. Antagonistic interactions with trace minerals and other food components form insoluble complexes that are poorly absorbed by the animal. Positive effects of organically bound to inorganic trace elements were confirmed in numerous scientific studies (Kincaid et al,. 1997; Nockels et al., 1993; Wedekind et al., 1992). Nevertheless, an adequate assessment of the quality of organically bound trace elements must be taken. It should be noted at this point

that the products on the market significantly differ in quality and that can be checked by simple analytical methods (Helle and Kampf 2008). Traditionally, minerals have been categorized as either organic

or inorganic. In 2012 a new category of trace minerals, known as hydroxy trace minerals, obtained EU approval as a feed additive for all animal species. These new products (di copper chloride tri hydroxide – Cu2 - Zn5

(OH)3 Cl2 (OH)8 (H2

Cl – and zinc chloride hydroxide monohydrate O) – brand name: IntelliBond®) belong to the group

of inorganic trace mineral sources, but have similar chemically stable structures as organically bound trace elements. Covalent bonds and a unique crystalline matrix structure provide a reliable stability, which differentiates hydroxy trace minerals from other organic or inorganic minerals. In addition, there are major advantages from a nutritional point of view. In comparison to copper sulphate, these products are non-hygroscopic and virtually insoluble at neutral pH which provides increased trace mineral stability in premix and food. Less reactive trace element ions occur in the upper digestive tract, which is associated with fewer interactions with other feed components. There are already numerous studies that demonstrate in comparison to sulphates the better protection of feed components (Lu et al., 2010; Miles et al., 1998; Pang and Applegate 2006). Due to the crystalline structure the trace elements are slowly released over the full length of the small intestine resulting in more efficient trace element absorption. Trial results in multiple animal species confirm the superior effects compared to sulphate and comparable effects to chelates (Allee et al., 2011; Cheng et al., 2008, 2010, 2011; Luo et al., 2005; Miles et al., 1998; Spears et al., 2004; Shao et al., 2010; Yasui et al., 2012).

Increase nutrient stability in premix and food Vitamin and fat stability, as well as nutrient availability improve by using stable trace element sources e.g. chelates or hydroxy trace minerals in comparison to sulphate forms (Miles et al., 1998; Lu et al., 2010; Luo et al., 2005; Banks et al., 2004; Liu et al., 2005; Pang and Applegate 2006; Shurson et al., 2011; Kampf, 2012). All these

10 20 30 40 50 60 70

0 0 10 20 Storage time (d) * Within a time point, mean is significantly different from Control (p<0.05).

Graph 1: Impact of various copper sources on the concentration of vitamin E in feed (Lu et al. 2010)


Control (18 ppm) Cu sulfate (200 ppm) IntelliBond C (200 ppm)

* * * *

Feed Vitamin E (mg/kg)

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