Page 657 - Small Animal Clinical Nutrition 5th Edition

680 Small Animal Clinical Nutrition

Copper 1989). Inadequate zinc supply, especially in growing animals,
VetBooks.ir Copper plays an important role in the metabolism of collagen causes severe clinical signs within days, including growth
depression,skin defects,impaired immune function and growth
and elastin. The copper-dependent lysyl oxidase is specific for
connective tissue and functions biologically to catalyze the
disorders of the skeleton. These disorders may be linked to the
oxidative deamination of the ε-amino groups of lysine and role of zinc as a cofactor in enzymes that are important for con-
hydroxylysine to form allysyl or hydroxyallysyl residues (Harris nective tissue metabolism. A low activity of alkaline phos-
et al, 1980; Siegel, 1979). This step forms intermolecular cross phatase (<300 IU/l) is a good indicator of a low zinc status (i.e.,
links between collagen fibrils, and is therefore essential for sta- deficient zinc intake) in growing animals and young dogs
b
bilization of connective tissues (Eyre et al, 1984). (Kirchgessner, 1987). There are no reports that excessive zinc
In several animal species and in people, copper deficiency intake is detrimental to skeletal development in dogs; however,
induces severe skeletal disease (Danks, 1980). Dietary copper excess zinc is presumed to be toxic at higher levels, as observed
levels less than 1 mg/kg DM were related to severe growth in other species.
deformities, fractures, wide “knotty” epiphyses and especially The essentiality of zinc for skeletal development is unequiv-
severe hyperextension of the limb axis in growing dogs (Baxter ocal; reports are available for many species describing severe
and Van Wyk, 1953). In young beagles, clinical signs of copper growth disorders induced by zinc deficiency (Hambidge et al,
deficiency were less severe than those previously reported; how- 1986). Zinc deficiency in dogs is of practical importance main-
ever, hyperextension of the forelegs was a characteristic feature ly with regard to skin diseases (NRC, 2006) (Chapter 32).
(Zentek et al, 1991). Feeding a low-copper food (1.2 mg/kg Skeletal abnormalities have been described in Alaskan mala-
DM) vs. a normal copper food (14.1 mg/kg DM) resulted in mutes with an inborn error in zinc metabolism (Smart and
depletion of plasma (1.4 vs. 9.7 µmol/l) and liver copper stores Fletch, 1971; Brown et al, 1978) and skeletal malformation in
(19 vs. 246 mg copper/kg DM). Secondary copper deficiency bull terriers with lethal acrodermatitis enteropathica, a geneti-
resulted in osteoporotic lesions in growing Great Dane pup- cally determined defect of zinc metabolism (Jezyk et al, 1986).
pies, which could be attributed to impaired osteoblastic func- Experimental zinc deficiency in beagles leads to a significant
tion (Read et al, 1989). These dogs were fed an experimental decrease of zinc concentrations in the skeleton especially in
food containing high concentrations of molybdate, which metaphyseal bone, which represents newly formed tissue. It is
strongly impaired copper absorption and induced secondary unknown to what extent marginal zinc intake, due to either
copper deficiency. subnormal dietary zinc concentrations or high concentrations
The overall prevalence of primary copper deficiency (i.e., a of interacting substances (e.g., phytic acid, calcium, copper, low
dietary deficiency) should not be overestimated. Most common digestible carbohydrates) (Zentek, 1995), contributes to DOD.
ingredients are rich in copper; however, some homemade, Foods for growing dogs should contain enough zinc to com-
unsupplemented foods (made of rice, dairy products, fat, starch) pensate for negative interactions with other dietary ingredients,
may contain low or suboptimal copper concentrations. Under especially if the originally balanced food is “improved” by dog
certain circumstances, these foods may contribute to the devel- owners who add large amounts of calcium carbonate or other
opment of skeletal disease, even if copper levels are higher than calcium salts.
in deficient experimental foods. A suboptimal copper supply Canine growth foods should contain 100 mg/kg DM zinc
could evoke negative effects especially if combined with high (NRC, 2006). Most commercial canine growth foods contain
growth intensity or other dietary imbalances (e.g., calcium, zinc higher levels of zinc to ensure this recommendation is met.
or carbohydrates).The possibility that large dogs are more sus-
ceptible to a low dietary copper intake cannot be excluded. Iodine
Impaired copper absorption may also occur with high dietary Iodine is essential for function of the thyroid glands (Belshaw
calcium or zinc levels; the latter induces copper binding metal- et al, 1975). The amino acid tyrosine is iodinated and, in sub-
lothionein in the gut mucosa (Brewer et al, 1992). High sequent metabolic steps, T and the biologically more active
4
amounts of poorly digestible carbohydrates or foods that are form T are formed. Both hormones, but particularly T , influ-
3
3
rich in certain types of dietary fiber may also reduce copper ence normal maturation of growing cartilage, penetration of
absorption (Zentek, 1995). capillaries and mineralization of newly formed bone. Thyroid
The recommendation for copper in canine growth foods is hormones stimulate formation and resorption of bone, which
11 mg/kg (DM) (NRC, 2006). Most commercial canine results in remodeling of the skeleton (High et al, 1981). Boxers
growth foods deliver copper in the range from 11 mg/kg to 20 with congenital hypothyroidism were found to have shortened
mg/kg (DM) and, therefore, meet this recommendation. limb bones and severe disturbances of the ossification and min-
eralization process, problems that were alleviated by L-thyrox-
Zinc ine supplementation (Saunders and Jezyk, 1991).
Zinc is an essential trace element that is widely distributed in Low dietary iodine induces dysfunction of the thyroid
the body. It serves as an important coenzyme in numerous bio- glands. Goiter (enlarged thyroid glands) develops with extreme
chemical processes.The zinc concentration in newborn puppies deficiency. In some regions of the world, goiter still occurs in
is about 22 mg/kg body weight and concentrations increase to dogs because they are fed unbalanced, homemade rations
120 mg/kg in tissues formed during the growth phase (GfE, (Kienzle and Hall,1994).Stunted limb development,hyperpla-