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Taurine and the other 21 amino acids.
There seems to be a lot of confusion, misinformation or misunderstanding the the world of foxes regarding amino acids. Everyone seems to only mention one of the amino acids (Taurine) saying how vital it is in the diet (which is not entirely correct), forgetting all 21 of the others.
This article seeks to clarify and hopefully help rehabbers, rescuers and those interested in learning, and helping to rectify myths and misinformation. Disclaimer: in this article I am not telling you wether you should or should not provide taurine to any foxes in your care, you are free to do either way, however this article simply provides facts for you to make up your own mind about, and to make you aware that taurine is just one of 22 canine associated amino acids. That said, foxes do not ordinarily need to consume Taurine** - now before you lose your mind from that bamboozle, please read on and it will all make sense.
Note: Minerals and Vitamins are not discussed in this article, neither are detailed descriptions of each amino acid or their function so not to over complicate the post.
Amino Acids - Foxes/Canines/Felines Foxes require 21 Amino Acids. 10 of which are Essential (need to be consumed) and the rest are synthesised in the body, by the body. The amino acid I will start with is Taurine, which is a non-essential amino acid in foxes, and the one I will focus most on since it is the one everyone talks about in the fox world and gets mostly wrong. Unlike other amino acids, Taurine is not made into proteins synthesised by the body, instead it remains as a free amino acid existing in many body tissues, including heart muscle, skeletal muscle, liver, retina of the eye, brain, nervous tissue, white and red blood cells, and mothers' milk and as a complex with bile salts excreted by the gallbladder. BUT, Taurine in canines/canids is a non-essential amino acid, which means it is not required in the diet because the body is able to synthesise its own within the body in the pancreas, providing there is sufficient methionine and cysteine. Felines (true carnivores) require Taurine in the diet, but Foxes are not felines or true carnivores, they are canines and omnivorous (despite being in the carnivora order of placental mammals). In fact, like wild wolves, foxes eat mostly plant matter in summer months when prey are less vulnerable and harder to catch seasonal fruits and plant matter is in abundance, and mostly flesh in winter months when prey is more vulnerable (sometimes known as prey vulnerability). This of course depends on the local availability of both and varies slightly on location. For wolves, this comes from years of real world in-situ studies on wild wolves in their natural habitat by conservation teams including examining scat to determine actual diet versus perceived diet, behaviour, tracking collars, etc). Since foxes are not true carnivores, and although their diets are similar to small felines, (mostly based on size and environment) the amino acid requirement for foxes versus felines has a couple of slight differences between the two species (cats for example also require the essential amino acid citrulline conditionally, although ordinarily if they have sufficient argenine this is converted to citrulline so it only really become essential if the feline has an argenine deficiency). Similar could be said of canids (and foxes) if there is insufficient methionine and cysteine, resulting in a potential deficiency in taurine production under unusual circumstances.
So what are all the amino acids that foxes / canines need? NON-ESSENTIAL AMINO ACIDS - are synthesised in the body, by the body, therefore they are not usually required in the diet**. Taurine is one of these amino acids. ESSENTIAL AMINO ACIDS - are those the body cannot synthesise and therefore need to be consumed in the diet. The confusion may have come by a misinterpretation/misunderstanding of the terms essential and non-essential by the layperson and social media or the internet perhaps. This in basic terms refers to whether they are essential to be consumed in the diet or not, it does not mean whether it is essential to the body itself as they are all required by the body, only that some are synthesised internally and others need to be consumed. So for canids (including foxes); Taurine does not usually need to be consumed, however, see below.
Older Foxes
As the body ages, when animals are much older, Taurine production within the body slows, so adding taurine to the diet much later in life can have some life prolonging benefits but in early life it is usually not required in the diet, since as previously stated the body produces its own. Symptoms of taurine deficiency can be similar to a stroke, cardiac heart issues (including but not limited to taurine deficiency related dilated cardiomyopathy) or ocular problems. It should be noted that at the time of writing this article, in the many hundreds of foxes I have treated so far, non of them have exhibited symptoms of stroke or taurine deficiency, including severely malnourished patients.
ESSENTIAL AMINO ACIDS (canines) Argenine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine NON-ESSENTIAL AMINO ACIDS Taurine - (essential only for true carnivores [felines]. Taurine synthesis in canines/canids occurs in the pancreas with sufficient levels of methionine and cysteine). Alanine Asparagine Aspartate Cysteine Glutamate Glutamine Glycine Proline Serine Tyrosine
Citrulline - (conditionally essential for felines with argentine deficiency) ** There are times when the body can develop a difficulty converting amino acids and may require supplementation to the diet during treatment. This can be condition specific, birth defect or serious injury. Supplementation is usually best done from natural sources for best absorption bioavailability although synthetic sources do exist, particularly in emergency medical situations.
Sources or related studies of interest (more are added periodically as they are found or produced, this is not an exhaustive list and there will inevitably be many not listed. If there are any of particular interest that you do not see here, feel free to reach out with link or description for it to be potentially added to help others):
FEDIAF is the trade body representing the European pet food industry for canines, felines and small animals across 15 national trade associations in 15 countries https://europeanpetfood.org/self-regulation/nutritional-guidelines/
Peer-Reviewed Research Studies on Diet-Associated DCM
Kaplan JL, Stern JA, Fascetti AJ, et al. Taurine deficiency and dilated cardiomyopathy in golden retrievers fed commercial diets. PLoS One 2018;13(12): doi: 10.1371/journal.pone. 0209112.
Adin D, DeFrancesco TC, Keene B, et al. Echocardiographic phenotype of canine dilated cardiomyopathy differs based on diet type. J Vet Cardiol 2019;21:1-9.
Ontiveros ES, Whelchel BD, Yu J, et al. Development of plasma and whole blood taurine reference ranges and identification of dietary features associated with taurine deficiency and dilated cardiomyopathy in golden retrievers: a prospective, observational study. PLoS One 2020;15(5): doi: 10.1371/journal.pone.0233206.eCollection 2020.
Adin D, Freeman LM, Stepien R, et al. Effect of diet type on circulating taurine concentrations, cardiac biomarkers, and echocardiograms in four dog breeds. J Vet Intern Med 2021;35:771-779.
Freid KJ, Freeman LM, Rush JE, et al. Retrospective study of dilated cardiomyopathy in dogs. J Vet Intern Med 2021;35:58-67.
Smith CE, Parnell LD, Lai C-Q, Rush JE, Freeman LM. Investigation of diets associated with dilated cardiomyopathy in dogs using foodomics analysis. Sci Reports 2021; 11, 15881.
Bakke AM, Wood J, Salt C, et al. Responses in randomized groups of healthy, adult Labrador retrievers fed grain-free diets with high legume inclusion for 30 days display commonalities with dogs with suspected dilated cardiomyopathy. BMC Vet Res 2022;18:157.
Cavanaugh SM, Cavanaugh RP, Gilbert GE, et al. Short-term amino acid, clinicopathologic, and echocardiographic findings in healthy dogs fed a commercial plant-based diet. PLoS One 2021;16(10):e0258044.
Freeman L, Rush J, Adin D, et al. Prospective study of dilated cardiomyopathy in dogs eating non-traditional or traditional diets and in dogs with subclinical cardiac abnormalities. J Vet Intern Med 2022;36:451-463.
Haimovitz D, Vereb M, Freeman L, et al. Effect of diet change in healthy dogs with subclinical cardiac biomarkers or echocardiographic abnormalities. J Vet Intern Med 2022;36:1057-1065.
Karp KI, Freeman LM, Rush JE, et al. Dilated cardiomyopathy in cats: Survey of veterinary cardiologists and retrospective evaluation of a possible association with diet. J Vet Cardiol 2022; 39: 22-34
Quest BW, Leach SB, Garimella S, Konie A, Clark SD. Incidence of canine dilated cardiomyopathy diagnosed at referral institutes and grain-free pet food store sales: A retrospective survey. Front Anim Sci 2022.
Walker AL, DeFrancesco TC, Bonagura JD, et al. Association of diet with clinical outcomes in dogs with dilated cardiomyopathy and congestive heart failure. J Vet Cardiol 2022;40:99-109.
Adin DB, Haimovitz D, Freeman LM, Rush JE. Untargeted global metabolomic profiling of healthy dogs based on grain-inclusivity of diet and reevaluation after diet change in dogs with subclinical cardiac abnormalities. Am J Vet Res 2022;25: 2460/ajvr.22.03.0054.
Owens EJ, LeBlanc LL, Freeman LM, Scollan KF. Comparison of echocardiographic measurements and cardiac biomarkers in healthy dog eating non-traditional or traditional diets. J Vet Intern Med 2022 Dec 8. doi: 10.1111/jvim.16606. Online ahead of print.
Smith CE, Parnell LD, Lai C-Q, et al. Metabolomic profiling in dogs with dilated cardiomyopathy eating non-traditional or traditional diets and in healthy controls. Sci Rep 2022: https://doi.org/10.1038/s41598-022-26322-8.
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