The trace element zinc is often overlooked when it comes to the nutrition of today’s pet canine. While the consumption of the correct amount of zinc is vital to keep your dog healthy, it can be a delicate balancing act to ensure their diet doesn’t contain too much or too little. Here's everything you must know about zinc for dogs.
Traditionally, including zinc for dogs has not been seen as a major issue as so many foods are abundant in zinc (Kunkle, 1980). However, with the advent of home-cooked dog food meals and raw food diets, there is an increased potential for error when it comes to the zinc content of doggy diets (Schlesinger, et al. 2011).
Additionally, dogs can suffer from zinc toxicities if they ingest excessive amounts of zinc, whether from their diet or an alternate source. Owners and vets alike should be aware of the potential for zinc-related medical conditions, as a prompt diagnosis and initiation of therapy related to zinc for dogs is often essential for a positive outcome.
Why is Zinc for Dogs Important?
Zinc is found in dogs’ bones, muscles, livers, spleens, prostate glands and a variety of other anatomical locations. Among many other functions, zinc for dogs is essential to ensure the correct functioning of the metabolism, immune system, reproductive system and skin healing of a canine (Jon Hardy, 2016; PDF).
Zinc stores within the dog's body are limited, and it is essential that canines have a continuous supply of zinc in their diet to meet their daily requirements. As many of the everyday healthy and top rated foods and human foods consumed by pet dogs contain zinc (such as meat, eggs and dairy), it would be quite uncommon for an animal’s diet to be lacking in zinc, unless they had been placed on a restrictive diet by their owner.
Studies show how a lack of zinc in dogs can lead to a number of ill effects, including but not limited to: poor growth, inadequate healing abilities and skin disorders (Colombini, 1999).
It’s All About the Breed
There's research on the importance of zinc for dogs depending on the canine's breed, and their needs and prevalence of zinc-related health problems. Breed differences exist, and some breeds such as the Siberian Husky, Samoyed and Alaskan Malamute are far more prone to developing zinc deficiencies (Kunkle, 1980; Jon Hardy, 2016).
While there are a large number of potential side effects from a lack of zinc in dogs, the most reported zinc-related medical condition seen in these particular breeds in scientific literature is known as “zinc responsive dermatosis.” This is a skin disease that responds to supplementation with zinc (White, et al; 2001).
Studies have also found that all breeds of rapidly growing large or giant puppies can be more prone to developing a zinc deficiency than smaller breeds. These dogs tend to either be on inappropriate diets or may be receiving dietary supplements which interfere with zinc absorption. Most commonly, vets observed that these dogs are receiving too much Calcium or Phytate.
Symptoms of zinc deficiency in dogs of these breeds are similar to those experienced by Northern breeds suffering from zinc responsive dermatosis, though they may also have thickened pads and irregular skin on their nose (Vitale, 2004).
Zinc Responsive Dermatosis
Owners of the susceptible Northern breeds of dog should be on the lookout for the tell-tale periocular crusting, nasal lesions and crusty, scaly skin seen in zinc responsive dermatosis. Anecdotally, their coat has been described as dull and lacklustre.
Secondary skin infections in dogs are seen frequently and may result in pruritus and scratching. Importantly, the condition tends to predominate between the months of September and April, which is when most dogs present to their local vet will display symptoms, according to studies (Colombini, 1997).
Interestingly, these dogs are not typically fed diets lacking in zinc, and increasing the amount of zinc for dogs of these breeds would not help. Instead, they are unable to adequately absorb the zinc available in their diet.
Diagnosis of affected animals involves blood tests and biopsies of visible skin lesions.
Affected dogs require oral supplementation of zinc, and a usual starting dose of zinc for dogs through supplements is 1mg/kg SID (Colombini, 1999). The most common form of supplementation is via oral tablets, which can be added to the dog’s food, crushed if necessary or given with pill pocket treats.
In an article written by Dr. Vitale on canine zinc-responsive dermatosis, a veterinarian who has extensively studied zinc for dogs and its related conditions, he recommends that the zinc not be given to a dog on an empty stomach, to both increase its absorption and decrease the risk of the supplement being vomited. IV supplementation and diet alterations have also been reported as potentially effective approaches.
Lethal Acrodermatitis in Dogs
Another reported condition of significance is a very rare clinical disease called “Lethal Acrodermatitis” that is thought to be caused by either copper or zinc deficiency in dogs, but specifically noted in studies with Bull Terriers (Uchida, et al; 1997).
Lethal Acrodermatitis in dogs is thought to be caused by a true dietary deficiency, rather than a malabsorption issue, such as is experienced by the Northern dog breeds mentioned above. In studies, affected Bull Terriers exhibited signs from a young age, including diarrhea, stunted growth and even aggression. While this disease is very uncommon, breeders of Bull Terrier puppies should have it on their radar.
Zinc for Dogs Supplementation
While the benefit of supplementing deficient dogs with zinc is obvious, the question arises as to whether we should be supplementing all dogs with additional zinc.
So should you give your pup additional zinc?
Like with most nutrients, if your pup is already receiving a sufficient amount of zinc through daily feeding, then supplementation is unnecessary and might even be dangerous. However, many dog foods and homemade diets do not provide enough zinc for dogs, and thus it's possible that adding additional zinc can benefit your pet.
Research suggests that supplementing even a well-balanced diet with extra zinc for dogs can improve both their skin and coat quality (Marsh, et al; 2008). Similarly, studies in the human medical literature highlight the role of zinc as an important anti-oxidant and an element that serves to protect the skin among other benefits (Rostan, et al; 2002).
Can Dogs Have Too Much Zinc?
While many owners are concerned about potential zinc deficiencies in dogs, it is absolutely possible for dogs to suffer due to excessive levels of zinc in the dog's body too. In most cases, this has been observed through dogs consuming inedible items that contain zinc.
One reported case occurred in a one-year-old cross breed female dog who was presented to a veterinary clinic with a history of gastrointestinal upset and lethargy (Clancey, et al; 2012). She also had an immune-mediated haemolytic anaemia which was not responding to the standard corticosteroid therapy administered. Diagnostic imaging revealed metallic objects within her abdomen, and a zinc reading came back markedly high at 24.4ppm (with 0.7 – 2 ppm being the normal reference range). The objects in question turned out to be a pair of metallic die from a board game, and fortunately the dog fully recovered after the items were removed.
A review of zinc ingestion toxicity secondary to penny ingestion, in which three of the five dogs passed away, emphasizes the potentially fatal complications of the disease related to zinc toxicosis (Meurs, et al; 1991).
The significance of these two and other case studies is that they highlight the potential dangers that our pets are exposed to within the family home as related to zinc elements. This is particularly true in the USA and Canada, where some coins contain zinc and dogs obviously can have easy access to that (Latimer, et al; 1989).
Owners should also be aware of the high zinc content of other run-of-the-mill household items such as batteries, certain medications, paint and nuts and bolts, which quickly exposes them to zinc toxicosis. The risk is particularly high in young puppies who explore the world with their mouth and in breeds known to be scavengers such as the Labrador Retriever and Beagle.
100mg/kg of zinc salts is reported to be the LD50 by the MSD Veterinary manual. With some pennies containing 2440mg of Zinc, the potential for zinc toxicity in dogs after ingestion of this item in particular is very high (Richardson, et al; 2002).
Often a Diagnostic Challenge
Something veterinarians and pet owners alike should know is misdiagnosing zinc related health issues in dogs. One of the major issues when a dog is presented to a veterinary clinic and is suffering from zinc poisoning is that it is often confused with idiopathic immune-mediated haemolytic anaemia (Clancey, et al; 2002).
As both conditions cause characteristic haemolytic anaemia in dogs, it is absolutely essential that veterinarians screen for potential zinc toxicity by obtaining a thorough history from the owner (focusing on diet) and also by performing diagnostic imaging to screen for any potential metallic foreign objects.
Therapy of Zinc Toxicosis in Dogs
Stabilising a dog that is critically ill due to zinc poisoning is mainly achieved via supportive care within a hospital environment. Intravenous fluids, gastro-protectants, oxygen therapy and blood products all play a role in a dog’s recovery (Clancey, et al; 2002).
The critical aim is to remove the source of zinc at the earliest opportunity. If the zinc source has only just been ingested (within the last few hours) it may be an option to induce emesis so that the item can be vomited, avoiding more invasive treatment. This is usually achieved with an injection of Apomorphine hydrochloride subcutaneously (Lefebvre, et al; 1981).
Alternatively, an item that is still within the dog's upper GI tract may be removed via endoscopy. If neither of these options are suitable, it may be appropriate to perform an exploratory laparotomy to remove the offending object. It is vitally important that the animal is stabilized before going ahead with any surgery, as there is a risk of death intra-operatively in the unstable patient.
In the case report in the Clancey's 2002 study describing a young dog who ingested metallic die, the offending items were found to have moved along the tract into the rectum, and were manually removed without the dog necessitating an invasive surgery. While this technique was successful in this case, and the dog went on to make a full recovery, it is the study author’s opinion that waiting for the object to reach the rectum after a diagnosis has already been made, may be exposing the animal to dangerously high levels of zinc, and should not be the primary treatment option.
In addition to the above recommendations, the use of chelation as a therapy is described in the MSD veterinary manual. Ca-EDTA is administered to the patient at a rate of 100mg/kg/day I.V or SQ; however, there is a potential for kidney toxicity in dogs, so appropriate patient selection is essential and chelation is not advised for every patient.
In Summary
Zinc for dogs is a critically important element when it comes to the overall health of our furry friends. Owners of certain breeds, such as the Siberian Husky, need to pay extra attention to their dogs' zinc intake to prevent deficiencies from occurring.
Some diets can already be sufficient in dogs, and excessive or unnecessary supplementation of zinc for dogs must be avoided, because zinc toxicity can be incredibly dangerous and potentially fatal.
Generally, most vet recommended commercially prepared dog food diets should contain the correct levels of zinc and, unless there is a specific medical reason to do so, these diets should not be supplemented with additional zinc. Special care should be taken to ensure pet dogs do not have the opportunity to ingest household products containing zinc, which can result in fatal toxicities unless promptly treated.
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