Since this sub-category is “Nutrients A-Z” – and since I am always going on about zinc, I thought we might start with a short entry on the role, requirements and optimal sources of zinc in the canine diet.
In contrast to the never-ending tomes I compose on energy nutrients, I’m going to strive to be succinct in these entries – shall we see how I do with that goal?
ZINC is the second must abundant trace mineral in the body, after iron. It is an essential nutrient that must be ingested dietarily. Zinc is present throughout the body in low concentration, but in most tissues. It performs multiple critical functions and must be supplied at adequate levels consistently or deficiency states will result, from mild to severe. Zinc is essential but should not be taken in high doses or even moderately elevated doses over a long period of time. It is one of the nutrients most commonly underfed in home made diets, raw or cooked.
Zinc’s functions in the body can be divided into three categories; these are Catalytic, Structural, and Regulatory.
1) Catalytic – Zinc is known to act as either a catalyst or a cofactor in 200 enzymes – these in turn are involved in carbohydrate and protein metabolism, cell replication and wound healing.
2) Structural – Zinc plays an essential role in the structure and function of biological membranes and proteins; when cell membranes lose zinc they become more vulnerable to oxidative stress and suffer functional impairment.
3) Regulatory – Zinc is also needed for “stabilization of DNA and RNA ( NRC, Nutrient Requirements of Dogs, 2006 pg. 173) functioning as a cofactor in the synthesis of both. Zinc “finger proteins” regulate gene expression “acting as transcription factors (binding to DNA and influencing the transcription of specific genes). Zinc also plays a role in cell signaling and has been found to influence hormone release and nerve impulse transmission.” Linus Pauling Institute page on zinc here
In plain language – zinc plays a role in immune function , protein synthesis , wound healing , DNA synthesis, and cell division. Zinc also supports normal growth and development for your growing dog.. A daily intake of zinc is required to maintain a steady state because the body has no specialized zinc storage system.
For humans, the RDA for adults for zinc is 15 mgs daily.
For dogs, whose sizes range from teacup to Great Dane, a little more calculation is involved.
The National Research Council has provided us with an Adequate Intake/Recommended Allowance for dietary zinc for dogs. It is 2.0 mgs/ KGbw/0.75. What this means is; to figure out what an individual dog should take in, we first need to take the body weight in kilograms to the power of 0.75 – this number is used to calculate all dietary requirements, including energy. With zinc, the number we arrive at is multiplied by 2.0. So let’s look at a 50 pound dog, once again;
Pounds = 50, so kgs = 22.68 kilograms
Now take that number to the power of 0.75 – using the Microsoft calculator on your computer, set to Scientific, that function looks like this: x^y
Now you have the “magic number” – 10.39
Next,multiply this number by 2.0 and you have 20.78 mgs – let’s say, 21 mgs daily. So a fifty pound dog requires MORE daily zinc than a 150 pound human does. In a weekly batch for a fifty pound dog – which is what I often recommend and what I do myself much of the time – that’s 147 mgs. Depending on the fiber content of the diet, we might want to go a little bit higher than that. But let’s look at the 21 mgs a day – if our fifty pound dog is not very active, and eating 1200 calories a day, coming from turkey, beef liver, brown rice, and sardines, we might end up with about half that amount. Although the foods are fresh, home prepared and healthy, carbs low and glutenfree – the recipe is still seriously low in zinc. Over time, immune system issues, skin issues, other problems arise that – chances are – your vet, even holistic vet, may not diagnose.
The moral of this story is don’t depend on food alone for adequate levels of zinc. If you’re doing a home made diet, you need to supplement. Do the math, and supplement accordingly. Why go to all the work of shopping cooking measuring and feeding home made diet, only to shortchange your dog on one of the essentials?
“Canine and Feline Nutrition:A Resource for Companion Animal Professionals” lists the following signs of zinc deficiency in dogs:
- growth retardation in pups
-testicular atrophy, impaired reproductive function
- immune system dysfunction
- conjunctivitis, skin lesions
“In dogs and cats, skin and hair coat changes are usually the first clinical signs of zinc deficiency; these signs have been described as dull, coarse hair coat and skin lesions that show parakeratosis and hyperkeratinization*” (Canine and Feline Nutrition, pg. 48) This is of interest to me as a nutritionist, as I see so many cases of poor coat where the owner immediately started to supplement fatty acids (which may or mat not be in need of supplementation). In either case, if the poor coat is related to zinc deficiency, fish oils will no help it. Adding supplemental zinc to recommended levels, or putting the dog on a diet formulated with AAFCo or NRC levels and ensuring they eat adequate amounts of it, will. Note there are many causes of poor coat, but fatty acids always seem to be what owners – and vets – will go to first.
Parakeratosis: dry, flaking, scaly skin
Hyperkeratinization: a disorder of the cells lining the inside of a hair follicle. It is the normal function of these cells to detach or slough off from the skin lining at normal intervals. The dead cells are then forced out of the follicle (primarily by the growing hair). However, in hyperkeratinization, this process is interrupted and a number of these dead skin cells do not leave the follicle because of an excess of keratin, a natural protein found in the skin. This excess of keratin, results in an increased adherence/bonding of dead skin cells together. This cohesion of cells will block or “cap” the hair follicle (leading to keratosis pilaris) or clog the oil duct (leading to acne).
The NRC Guidelines states that “zinc is a relatively nontoxic substance and dietary deficiencies are much more likely to occur than are excesses” (NRC pg 175) Clinical signs of (rare) zinc toxicity, usually from ingestion of metallic objects, include acute gastroenteretis, hemolytic anemia and lethargy. However, it is still important to monitor zinc levels due to it’s interactions with other minerals, especially copper, iron and calcium. More on this in Nutrient Interactions (below). It is worth noting that the current trend to amping up zinc for humans during a cold or other infection is no substitute for maintaining good zinc levels all year round! Strong immune function depends regular levels of zinc more than sudden, sweeping “therapeutic” doses.
Although this is related to humans, it may be of interest here as well. Acute toxicity has been reported:
“Isolated outbreaks of acute zinc toxicity have occurred as a result of the consumption of food or beverages contaminated with zinc released from galvanized containers. Signs of acute zinc toxicity are abdominal pain, diarrhea, nausea, and vomiting. Single doses of 225 to 450 mg of zinc usually induce vomiting. Milder GI distress has been reported at doses of 50 to 150 mg/day of supplemental zinc. Metal fume fever has been reported after the inhalation of zinc oxide fumes. Specifically, profuse sweating, weakness, and rapid breathing may develop within eight hours of zinc oxide inhalation and persist 12-24 hours after exposure is terminated.”
Linus Pauling Institute, page on zinc
The major complication of less extreme, longterm overdose is copper deficiency.
By far the highest concentration of zinc in food is found in oysters; most of us, however, are not going to include these in our dog’s daily diets, although I have known some who tried (and there are other problems associated with daily feeding of fish and seafood, which I’ll be going into in detail in the section on protein). More reasonable sources for the average home feeder include:
Beef- 5 ounces of lean, cooked brisket has almost 10 mgs
Pork- 5 ounces lean cooked pork loin – 3.5 mgs
Turkey- 5 ounces darkmeat with skin, cooked, 5.6 mgs
Lamb- 5 ounces lean leg, cooked – 5.8 mgs
Liver, beef and calves: Beef liver is a good source with 4.5 mgs per 3 ounces of cooked weight, but calves liver has almost twice that amount with 8 mgs pre 3 oz serving. beef liver is higher in copper though – again almost twice the level – so decide what you need most and add accordingly.
Other foods contribute to the total zinc content, but less so, and much of the zinc in foods like rice and lentils is offset by phytate. I consider turkey, beef, lamb and pork among the best choices for dietary zinc, for dogs. For interests sake, here’s a few more foods high in zinc (we can have some, too!) Each 100gram serving of the foods below contains:
Pumpkin seeds- 7.5 mgs
Brazil Nuts- 4.2
Oatmeal, cooked – 3.2s
Split peas, cooked – 4.2
Buckwheat, cooked – 2.5
Check the zinc content of your dog’s food at http://www.nutritiondata.com and always remember that any single food you use will have other nutrients too, so analyze your full recipe, and supplement according to what is missing or low. Copper is often low as well, so balance it all out carefully.
Something we as dog lovers should be area of is zinc’s potential effect on some antibiotics – as much as we hate to give them, they are occasional necessities, and even life savers. Zinc supplementation may decrease absorption of some antibiotics, so do give them away from food or discuss with your vet. There is no need, if making a balanced home made diet, to leave the zinc out during a round of antibiotics. This applies to supplemental zinc added above and beyond the RA, such as one might use during infection or therapeutically to reduce copper levels. Not a huge concern, but something to be aware of.
Some types of diuretic, especially used longterm, may increase need for dietary zinc. Again – please discuss with your veterinarian.
- Ciprofloxacin (Cipro)
- Levofloxacin (Levaquin)
- Ofloxacin (Floxin)
- Moxifloxacin (Avelox)
- Norfloxacin (Noroxin)
- Gatifloxacin (Tequin)
- Minocycline (Minocin)
- Demeclocycline (Declomycin)
However, doxycycline (Vibramycin) does not seem to interact with zinc.
Cisplatin (Platinol-AQ) — This drug, used for chemotherapy to treat some types of cancers, may cause more zinc to be excreted in the urine. If your dog is undergoing chemotherapy, do not give additional zincwithout talking to your oncologist.
Deferoxamine (Desferal) — This medication, used to remove excess iron from the blood, also increases the amount of zinc that is lost in urine.
Immunosuppressant medications — Since zinc may make the immune system stronger, it should not be taken with corticosteroids (such a prednisone), cyclosporine, or other medications intended to suppress the immune system.
Nonsteroidal anti-inflammatory drugs (NSAIDs) — Zinc interacts with NSAIDs and could reduce the absorption and effectiveness of these medications.
Penicillamine – This medication, used to treat Wilson’s disease (where excess copper builds up in the brain, liver, kidney, and eyes) and rheumatoid arthritis, decreases the levels of zinc in the blood.
Thiazide diuretics (water pills) – This class of medications lowers the amount of zinc in the blood by increasing the amount of zinc that is passed in urine. These include
- Chlorothiazide (Diuril)
- Chlorthalidone (Hygroton)
- Indapamide (Lozol)
- Metolozone (Zaroxolyn)
- Polythiazide (Renese)
- Quinethazone (Hydromox)
- Trichlormethiazide (Metahydrin, Naqua, Diurese)
Zinc, as has been mentioned interacts with copper, iron and calcium, and is adversely affected by high dietary phytate. There are other less wellknown interactions, especially the connection with Vitamin A - we could go into much detail about all of them but at the very least I to touch on them here . For those who think that all this calculating of numbers and percentages and so on is unnecessary micromanagement, read on. The mineral levels are critically important, and become even more so for a growing dog or one under stress or dealing with illness. Zinc is affected by, and can also affect, many other essential nutrients – goog reason to find the right levels for your own homefed dog, and stick with them.
Dietary phytate reduces the absorption of zinc, and if excess presence is combined with overly high levels of calcium, a deficiency scenario can develop, even when adequate levels of zinc are provided in the diet. Phytate – as discussed in the carbohydrate thread, is a chemical found in many plants, and has both benefits and undesirable aspects. Whenever a food rich in phytate comprises a significant part of the diet, steps should be taken to reduce it, as in pre-soaking and overcooking brown rice. In some cases elevated minerals may be added, but this is an individual call and not all dogs can or should have mineral elevation to compensate for phytate. The ideal solution is to feed controlled amounts of foods with phytate, and keep minerals in the RA range. Brown rice and lentils, while beneficial foods for the dog in reasonable quantities, contain significant levels of phytate;cooking does reduce it significantly.
High zinc intake adversely affects copper status and absorption; many home made diets are marginally to seriously low in copper to begin with. The optimal ratio between zinc and copper is 10:1. If zinc is elevated for any reason, copper levels should be raised too. The exception to this is of course, copper-storage disease, in which high levels of zinc are used therapeutically to chelate (bind to and remove) copper from the body. Often home made diets are low in copper as well, so either add copper-rich foods like beef liver when adding zinc, or supplement with both, to ensure copper levels stay optimal, too.
CALCIUM and IRON: Both of these minerals can impair the absorption of zinc, even when adequately represented in the diet, if they are overfed. I often see home made diets which are not only low in zinc but very high in calcium and iron ( this is the classic RMB scenario where beef is the main protein source). Be sure to check the required levels of both calcium and iron, and make sure they are not excessive, or you can still experience the many issues associated with even mild zinc deficiency. It can take years to show up, so prevention is key.
Zinc and vitamin A interact as well, although this has not been as well studied in the dog as in humans.. Zinc is a component of retinol-binding protein,which is necessary to carry vitamin A in the blood. Zinc is also required for the enzyme that converts retinol (vitamin A) to retinal.Retinal s necessary for the synthesis a protein called rhodopsin, present in the eye; this protein is needed for the eye to adapt to the dark properly. Low levels of zinc is associated with decreased release of vitamin A from the liver, which may contribute to symptoms of night blindness .
Zinc supplements are available in a number of forms; citrate, picolinate and gluconate are all popular versions.
The inorganic forms of zinc found in multivitamins are usually not absorbed very well in human studies; zinc is most bioavailable when it is bound to a ligand/chelator (such as EDTA), amino acid (such as histidine) or organic acid (such as citrate) . Zinc methionine is an exception, with studies showing it to have low bioavailability equal to that of the inorganic forms chloride and proprionate, and it is hypothesized that the bond is not strong enough to survive the upper GI tract . Zinc picolinate is one of the most bioavailable forms .
“Chelated” means connected with another molecule. These include organic acids such as picolinic acid, orotic acid, citric acid and gluconic acid.These are the forms of zinc I use and recommend in my diets. No inorganics – sulfate and oxide. Zinc methionine has the above-mentioned controversy about it, so I stick to the gluconate, citrate and picolinate forms
It’s good to know that zinc oxide, often used in cheaper commercial dogfoods, is not considered a highly bioavailable form at all and should be avoided. I see a number of foods now that are trying to appear “premium” and are in fact, better than some f the truly abominable products, but still cutting corners where consumers aren’t likely to notice. Minerals in oxide form is a big red flag. I prefer not to use sulfate, but stick with the chelated forms.
- In humans many factors can increase the need for zinc – but many, such as alcohol consumption, do not apply to dogs. There may be a need for extra zinc in dogs with kidney disease, pancreatitis, IBD (Inflammatory Bowel Disease) any type of infection, diabetes, liver disease, EPI (exocrine pancreatic insufficiency) or who are on a vegetarian diet.
- Dogs who require a high fiber diet, such as those with pancreatitis, should have zinc given separate from meals if at all possible.
- Zinc malabsorption occurs in several breeds of dogs, notably the Alaskan Malamute, Siberian Husky, Great Dane and Doberman Pinscher. The syndrome usually shows up at about a year old and manifests frequently with quite severe dermatological symptoms; Owners almost always will take the dog to the vet at this point and oral supplementation resolves the issue, although much higher amounts of zinc are used than for dogs with normal absorption capacity. More on this issue here
If you are feeding a home made diet unsupplemented with zinc, chances are your dog is in need of some. Run your recipe through nutritiondata.com and check the amounts against his requirement, as explained above. Low zinc can contribute to skin and coat problems, if your dog has any poor coat or skin issue, evaluate dietary zinc as part of your strategy.
Don’t stress, but take this one to heart. Its all too often overlooked as something that “variety” will take care of – and trust me, it won’t.
Canine and Feline Nutrition, A Resource for Companion Animal Professionals
Nutrient Requirements of Dogs, National Research Council, 2006
Encyclopedia of Nutritional Supplements, Michael T. Murray
Linus Pauling Institute