Zinc - Nutrition

What is Zinc?

Zinc is an essential mineral and belongs to the group of nutrients called the trace elements. These are essential minerals but are designated as such because they are required in much smaller amounts than major minerals such as calcium and phosphorus. Dietary zinc exists in the divalent form (Zn²⁺) and is involved in many aspects of metabolism, mainly in enzyme-mediated reactions.

Why is it Important?

Zinc has many essential functions in the body, it is a co-factor or catalyst in at least 200 zinc-containing enzymes that are involved in protein, carbohydrate, nucleic acid and lipid metabolism.

Roles in the Body

Zinc plays a crucial role in skin function and wound healing, cell replication, the structure and function of biological membranes as well as the stabilisation of the nucleic acids. It is absorbed mainly in the small intestine, the highest rates occurring in the jejunum. Various dietary factors affect the absorption of zinc, in particular high intakes of calcium, iron and phytate, all of which reduce its availability.

Consequences of Zinc Deficiency

Dog:

There are two principal sets of information on zinc deficiency in puppies and adult dogs. The first involves reports of experimentally-induced zinc deficiency. These investigations used low levels of zinc and enhanced levels of calcium, which is known to interfere with zinc absorption. Robertson and Burns observed deficiency signs in puppies fed dietary zinc at 33 mg/kg with a calcium content of 1.1%, both values on a dry matter (DM) basis. No adverse effects were seen in puppies fed 33 mg/kg zinc and 0.3% calcium or 133 mg/kg zinc with 1.1% calcium. These results were corroborated by Sanecki et al. who produced zinc deficiency in weanling pointer puppies fed up to 35 mg/kg zinc and 2.6% calcium, both on a DM basis. Control puppies fed the same dietary calcium level but 120 mg/kg zinc showed no signs of deficiency.

The second set of reports comes from naturally-occurring zinc deficiency syndromes. One occurs in northern breed dogs, typically Siberian huskies or Alaskan Malamutes, which is due to a genetic defect that interferes with zinc absorption. In one study huskies represented 76% of dogs with zinc-responsive dermatosis. Treatment requires lifelong dietary supplementation with a zinc content of 150 to 200 mg/kg DM. Another syndrome has been reported in which zinc deficiency is due to feeding cereal-based pet foods containing high concentrations of substances, such as phytate, that bind zinc and reduce its availability.

Recognised Syndromes related to Zinc Deficiency

1. Biochemical: Clinical findings include a decrease in total serum zinc and the serum concentration of enzymes requiring zinc.
2. Clinical: The typical clinical signs of zinc deficiency included poor puppy growth rates and serious skin lesions, which usually begin in areas of contact or wear such as the feet.

Cat:

There is little information on zinc deficiency in kittens or adult cats; the data comes primarily from a study by Kane et al., as detailed below.

Recognised Syndromes related to Zinc Deficiency

1. Biochemical: Concentrations of serum and liver zinc decreased in kittens fed dietary zinc levels of 0.7 and 4.8 mg/kg DM but were normal in kittens fed zinc at 52 mg/kg DM.
2. Clinical: Skin lesions (parakeratosis) and reduced growth rates were observed in kittens receiving the two lower levels as shown in (1.). Testicular degeneration occurred in kittens fed zinc at 15 mg/kg DM but not in those receiving 67 mg/kg DM.

Effects of High Zinc Intakes

Dog:

Zinc is of relatively low toxicity in dogs. In fact some studies have shown beneficial effects of zinc at concentrations higher than the accepted nutritional requirement. Marsh et al. reported that feeding a complete and balanced diet containing higher than normal levels of zinc (400 mg/kg DM) and linoleic acid (6% DM) to black Labrador retrievers for 9 weeks was associated with significant improvements in coat condition. Dogs fed the high zinc level on its own showed a significant decrease in transepidermal water loss. Therapeutic doses of zinc of about 20 mg/kg bodyweight/day (equivalent to a dietary zinc concentration of approximately 1100 mg/kg DM for a Bedlington terrier weighing 9 kg), have been given to certain dog breeds such as the Bedlington terrier, Labrador retriever, West Highland white terrier and Dobermann pinscher, which have an inherited defect that results in toxic excesses of copper in the liver, causing hepatitis and cirrhosis. Zinc supplementation is continued for 2 to 3 months, followed by halving the dose thereafter to block copper absorption and decrease copper accumulation in the liver.

Cat:

Sterman et al. fed adult cats a dietary zinc content of 600 mg/kg DM for 6 weeks with no apparent adverse effects, although the blood zinc concentration increased compared with control cats fed a zinc level of 100 mg/kg DM. This suggests that, like the dog, cats can tolerate zinc concentrations well above the nutritional requirement.

Dietary Sources

Zinc is fairly well distributed in raw materials used in dog and cat foods. Animal sources, such as red meats, fish meals and meat meals contain the highest amounts but cereal grains and in particular soybean, peanut and linseed meals also contain reasonable quantities. Nevertheless, to ensure nutritional adequacy most dog and cat foods are supplemented with zinc salts such as the chloride, carbonate, sulphate, lactate or acetate.

References

Endorsed by WALTHAM®, a leading authority in companion animal nutrition and wellbeing for over 50 years and the science institute for Mars Petcare.

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