In dogs, taurine is an amino acid mainly synthesized in the liver and central nervous system. In addition to its main function of conjugation of bile acids, taurine is thought to play an important role in the health of the myocardium, as it is the most abundant free amino acid in the heart.
Although not considered an essential amino acid, several studies have associated the nutritional deficiency of taurine with the development of dilated cardiomyopathy (DCM) and other pathologies (ocular, reproductive failure, growth retardation, central nervous system dysfunction, skeletal malformations and other). The particular complexity of the taurine metabolism in the dog seems to be a factor that can predispose to the development of its deficiency in conjunction with increased metabolic needs or intestinal malabsorption.
Different dog breeds, such as the Dobermann, Great Dane and Irish Wolfhound, present a hereditary form of DCM. Within these breeds, some research was conducted on the association between the taurine deficiency and the onset of DCM, with results that have not confirmed a clear and direct causal link.
Although it can be said that any breed is capable of developing DCM for insufficient taurine levels, some studies have shown that this pathology occurs more frequently in some dog breeds such as the Golden Retriever, the American Cocker Spaniel, the Newfoundlands, the Setters British and Labrador Retrievers. The fact that some dog breeds have an apparent increased risk of DCM related to diet suggests that genetic or metabolic differences may exist between dog breeds that make some more vulnerable to the development of this condition.
Numerous scientific studies have shown that there is an association between insufficient blood levels of taurine and the type of dog feeding. The first scientific evidence dates back to 2001 when a low protein diet with a deficiency of taurine and DCM was linked. Once the levels of taurine in the petfood were corrected, the cases of DCM secondary to the deficiency of this amino acid decreased considerably and were limited mainly to dogs fed on home diets, cooked or raw, if not correctly balanced in all nutrients. However, there is a poor understanding of how the plasma concentration of taurine is related to its concentration in the dog’s myocardium.
Recently, there has been an increase in the number of DCM cases suspected of being diet-related in Golden Retrievers. The purpose of this study is to describe the history of the diet, the echocardiographic results, the concentrations of taurine in the blood and the clinical outcomes in the Golden Retrievers diagnosed with DCM and low concentrations of taurine in the blood.
MATERIALS AND METHODS
The subject of the study were 24 Golden Retrievers, with an ultrasound diagnosis of DCM and low blood levels of taurine. A complete dietary history, anamnesis, echocardiography, blood tests and blood concentration of taurine before and after the change in diet was obtained.
For the purpose of this study, a low level of taurine was defined when it was below 250nmol/ml in whole blood, 60nmol/ml in plasma and 110nmol/ml in serum. These concentrations have been chosen based on the bibliography present, although specific reference ranges for Golden Retrievers have not yet been established.
The dogs object of the study were fed, on average for 2 years, with cereal-free croquettes (the so-called “grain free”) and that on the label had legumes among the top five ingredients. The foods were complete, balanced and formulated to meet AAFCO (Association of American Feed Control Officials) guidelines for dog nutrition, but which had not been tested for nutritional adequacy and which did not follow the WSAVA guidelines.
All dogs were prescribed a change of diet and a supplement of taurine at the median dose of 3000mg per day and 13 dogs were also added a supplement of L-carnitine at the median dose of 2000mg.
RESULTS AND DISCUSSION
All dogs in this study consumed similar diets: grain-free, uncommon protein-based or rich in legumes.
All dogs, except one, consumed less food than both their maintenance energy needs and the indications of daily ration recommended by the manufacturer, this could be associated with an inadequate intake of taurine and its precursors.
For 16 dogs we have one year follow-up data. In all but one dog, returning to a diet containing a certain percentage of cereals and taking a taurine and/or L-carnitine supplement led to an improvement in echocardiographic parameters, symptoms of the disease, increased plasma concentration of taurine and resulted in the discontinuation or decrease of cardiac drugs. This shows that DCM secondary to taurine deficiency can have a good prognosis, as cardiac changes are potentially reversible. On some subjects, however, this treatment has not led to any result, so the prevention of this pathology always remains the best choice.
The quantity of taurine can be influenced by various factors inherent in the techniques and processing conditions applied to the raw materials and the finished product, for example it is known that some cooking methods can determine important losses of this amino acid.
Animal muscle tissue has a higher amount of taurine than the other ingredients commonly used in petfood. In recent years there has been an increase in the use of protein sources, which until recently were not so commonly found in dog diets such as rabbit, deer, bison, lamb and wild boar. It was noted that some meats, such as rabbit and lamb, were found to be unexpectedly deficient in taurine, while for others, data regarding the amino acid composition and their bioavailability are scarce.
Legumes are increasingly present as ingredients in canine nutrition, but in addition to being almost taurine-free, like all plants, they are also deficient in sulfur amino acids (precursors of taurine) unlike most plants. In addition, legumes contain anti-nutritional factors such as proteolytic inhibitors and phytates which negatively influence the digestibility and bioavailability of the taurine precursors. Still legumes are rich in fiber and there is scientific evidence that certain sources of fiber cause a greater depletion of taurine in the stool since it is not reabsorbed.
Previously, it has been shown that dogs with a low energy requirement, fed with diets low in sulfur amino acids, show a lower synthesis of taurine, and therefore can benefit from higher concentrations of these precursors in the food.
These data underline the importance of obtaining a complete dietary history in canine patients suffering from heart disease.
CONCLUSIONS
In Golden Retrievers, the cause of DCM is most likely multifactorial, i.e. due to dietary, metabolic and genetic factors. In fact, even taking into account apparently healthy Golden Retrievers, there is a prevalence of low concentrations of taurine which could represent a breed specific sensitivity to this condition.
Although the correlation between nutrition, taurine deficiency and the development of DCM is clear, further studies are needed to better understand the potential interactions between specific food components, types of industrial processes and levels of taurine. To date, it is not yet possible to determine the exact causality of the deficiency of this amino acid and for this reason it is not possible to define without a shadow of a doubt what the dietary characteristics involved in the pathogenesis of DCM in dogs.