During my research for the cause of Allie and her littermate’s DCM, I met many people in different parts of the world who were all very helpful. They ranged from breed enthusiasts and breeders, to well known researchers who are experts in their field. They really went out of their way to provide me with information. 

I had read about a rare occurrence of spontaneous genetic mutation, and wondered if this was a realistic possibility. It seemed like the odds were against this happening with two puppies, but I had to ask! I also wondered if both of them could have simply been Taurine deficient. I reached out to a veterinary researcher, who answered my questions:

1. It is highly unlikely that a spontaneous mutation happened with both puppies
2. It is highly unlikely that both puppies are simply taurine deficient. It is more likely that it is multi factorial

For me, this helped to clarify that despite having no reports of DCM in their lineage, their DCM didn’t happen “out of the blue”. It is likely genetic, plus something else…maybe more than one other thing. Even though we didn’t test Taurine levels in either Allie or her littermate, it would be reasonable to assume they were both Taurine deficient based on a study I mentioned in Part 3 (Kittleson, 1997).

Other Possible Contributing Factors

In addition to genetics, Chagas’ disease, parvovirus, and infections transmitted from ticks, there are other numerous known causes (1):

This review covers the various etiologies known to cause DCM in dogs, including genetics, hypothyroidism, myocarditis, chronic tachycardia, and certain known dietary deficiencies (Phillips and Harkin, 2003; Sanderson, 2006; Wess et al., 2010b; Beier et al., 2015; Hallman et al., 2019; Vollmar et al., 2019). 

We know Allie and her littermate do not have myocarditis (infection of the heart) or chronic tachycardia (rapid heart beat). Since they were both being fed a raw diet, neither were affected by kibble with pulses (the seeds inside legumes: beans, chickpeas, lentils and peas). Neither have had parvovirus or had an infection due to ticks, or Chagas’ disease.

That leaves hypothyroidism. Neither Allie or her littermate have been tested for that, but they were both on the thin side when diagnosed, and hypothyroidism is usually associated with weight gain. Since we didn’t test their Taurine levels before being put on medication, we can only assume they were Taurine deficient because of their breed.

Allie came from a litter of four; three females and one male. To my knowledge, the other two littermates have not been tested for DCM or had their Taurine levels tested. As for their parents, one is clinically healthy and the other has not yet been tested. So we still have a few unknown factors to consider.

Diet and Nutrition

Even though Allie is fed a raw diet, I do use kibble for some training exercises and often for scatters in the grass. I even used grain-free kibble in small amounts prior to Allie’s diagnosis. We ruled it out as a contributing cause because the timeframe was too short, and the amount was too little. The paper I reference in this section helped me dismiss the idea that the kibble I used was even partially responsible.

As for the Taurine deficiency, there is still only speculation as to what causes this in Cocker Spaniels (1):

The reason for the low plasma taurine concentrations in these dogs is unknown. However, it is speculated that a combination of an enzyme deficiency, such as cysteine sulfinic acid decarboxylase, and loss through conjugation with bile salts may be the cause

Certain vitamin deficiencies have been linked with DCM: thiamine pyrophosphate, copper, vitamin E and selenium (1):

Dogs with DCM have significantly lower vitamin E concentrations and reduced glutathione peroxidase, which is involved in cysteine synthesis when compared with healthy dogs 

What causes the deficiency in vitamin E? In humans, it’s usually caused by a metabolic disorder. So does the same metabolic disorder that is assumed to cause Taurine deficiency, also cause vitamin E deficiency? (2)

Vitamin E deficiency is extremely rare in humans as it is unlikely caused by a diet consisting of low vitamin E. Rather, it tends to be caused by irregularities in dietary fat absorption or metabolism. Vitamin E is a lipid-soluble nutrient. 

Allie’s food has sufficient vitamin E, but I will investigate the need to supplement her diet.

In Part 2 I mentioned heavy metal as a factor in affecting Taurine levels. In this journal reference it describes an example of how this might happen, affecting the metabolism of both Taurine and Carnitine (1):

A commonly used ingredient in pet food is cassava (tapioca), which contains 10% arginine (Crawford, 1968). Cassava is known to accumulate cyanogenic glycosides, cyanide. When cyanide is consumed, it is converted into thiocyanate,

This can limit the availability of sulfur-containing amino acids used to biosynthesize taurine and carnitine. Additionally, cassava has been identified as a goitrogenic food.

So cassava has a double edged sword! It not only accumulates cyanide, which then alters the metabolism of Taurine and Carnitine, it can also contribute to the development of a thyroid problem. Cassava is often used in grain-free kibble.

The paper that I reference below states that the FDA 2018 report which speculates that pulses are responsible for diet-associated DCM may not be supported by evidence-based research. In a study conducted at the University of Illinois, they compared dogs that were fed 45% legumes to those that were fed a diet primarily comprised of poultry byproduct. There was no significant difference when comparing plasma amino acids, or plasma and whole blood taurine concentrations between groups (Reilly and de Godoy, 2019). This part stands out to me concerning legumes (1):

Therefore, since there was no change in taurine concentrations with dogs being fed a diet containing 45% legumes, legumes are more than likely not a cause of taurine-deficient DCM

Further supporting this, Kaplan et al. (2018) compared commercial diets being consumed by dogs diagnosed with DCM (1):

While all initial ingredients in the ingredient list were not reported, this study did report 12 out of 13 diets were grain-free and 10 out of 13 contained legumes in the first five ingredients. However, 22 out of 23 of these dogs were eating less than the maintenance energy requirements and brand suggested feeding guidelines.

This may have resulted in a suboptimal intake of sulfur-containing amino acids (Kaplan et al., 2018) and not pulse ingredients.

This statement raised the question that underfeeding can cause a deficiency leading to the development of DCM. The dogs weren’t described as being underweight (so possibly getting extra food from treats or table scraps) but rather under fed a balanced diet and not getting the required nutrients. If this is the case, it does make me wonder about working English Cocker Spaniels that are underweight and therefore possibly under fed. (Allie was initially underweight due to the stress of being impaled by the twig — see Part 1) (1).

Update on Allie

References

1. McCauley, Sydney R., et al. “Review of Canine Dilated Cardiomyopathy in the Wake of Diet-Associated Concerns.” Journal of Animal Science, vol. 98, no. 6, 1 June 2020, pubmed.ncbi.nlm.nih.gov/32542359/, https://doi.org/10.1093/jas/skaa155. Accessed 8 Dec. 2020.
2. Kemnic, Tyler R, and Meghan Coleman. “Vitamin E Deficiency.” Nih.gov, StatPearls Publishing, 14 Feb. 2019, www.ncbi.nlm.nih.gov/books/NBK519051/.