Food and Behaviour in dogs

M. A. Crisci, 12th October 2017

Believe it or not, behaviour can be affected by nutrition and ingredient selection. Good nutrition is vital for biological functions including those that act on behaviour. There isn’t much research into this area for dogs, but what’s available is fascinating. Could food be partly responsible for your dogs’ bad behaviour?

Nutrients and behaviour


Tryptophan is an essential amino acid for dogs and is a precursor of the ‘feel good’ hormone serotonin. High levels of tryptophan in the brain can increase serotonin production. Therefore, feeding more tryptophan levels may improve behaviours such as aggression in dogs (1,2).

Serotonin levels also influence satiety (appetite), heart function, pain and mood. Supplementation of tryptophan above dietary levels can reduce stress in a variety of species (1).

The concentration of dietary tryptophan compared to other competing ‘large neural amino acids’ is important. Foods may have a low ratio of tryptophan to other amino acids. A low ratio means reduced tryptophan uptake into the brain. The result: impeded serotonin production (1).

Evaluation of a commercial stress-relieving dog food

‘Canine Calm’ (Royal Canin, Aimargues, Gard, Franc) is supplemented with tryptophan and alpha-casozepine (another stress reducer). This diet has a high ratio of tryptophan to other large neural amino acids, to maximize brain uptake.

Canine Calm significantly reduced aggression, fear and sensitivity behaviours. Cortisol is often used as a stress biomarker. In this trial, urinary cortisol levels indicated reduced stress in dogs fed the study diet (3).


High concentrations of tyrosine and low levels of tryptophan in foods may also be important. In a calm animal, increasing dietary tyrosine has little effect on the production of its hormone predecessors: dopamine, noradrenaline and adrenaline.

In a stressed animal, brain noradrenalin levels are depleted which can be rectified by feeding high levels of tyrosine. The stress alleviating effect of supplemental tyrosine has been reported in a number of species (1).

Tyrosine is ‘non-essential’ to dogs, as it can be synthesised from phenylalanine (4). Dietary levels of both tyrosine and phenylalanine should be considered.

Amino acid availability

The bioavailability of amino acids will influence the production of hormones and neurotransmitters that affect behaviour. Meat, milk and egg products, along with soybean, some grains and pulses are good sources of tryptophan, tyrosine and phenylalanine.

High-quality animal protein sources are more easily digested in dogs than animal by-products and many plant sources (5). Highly digestible protein and high quality feed ingredients may provide more bioavailable amino acids.

Evaluation of food quality and behaviour

Kennelled dogs fed ‘premium quality’ vs. ‘basic’ diets showed reduced plasma cortisol levels, indicative of reduced stress (6).

A similar experiment looked at the behavioural responses of kennelled dogs fed basic and premium quality diets (table 1), with varied levels of human interaction. Premium food combined with increased human exposure improved behaviour (7).

Table 1. Key differences between ‘basic’ and ‘premium’ diets used. Table adapted from Hennessy et al, 2002 (7).

Tryptophan supplementation on a low protein diet has reduced aggression in dogs most when compared to a high protein diet without supplementation (2). This is likely to be because of an increase in tryptophan relative to other large neural amino acids.

Diets very low in protein and containing low quality protein are not recommended or beneficial for dogs! In the premium diet fed by Hennessy et al, 2002 (7), protein inclusion was higher, but so was quality and digestibility. Data suggests that the availability and source of protein may influence behaviour in dogs.

Fatty acids

N-3 polyunsaturated fatty acids (n3PUFA) with a particular stance on DHA have been investigated, with respect to cognitive function and behaviour in dogs. In rats, diets deficient in n3PUFAs have increased aggression and stress behaviours, while decreasing learning ability (1).

n3PUFA supplementation may increase brain serotonin levels, while n3PUFA deficiency may decrease serotonin in some animals (not yet studied in dogs) (1). Dogs with low levels of omega-3 fatty acids have shown increased aggressive tendencies (8).

Cognitive function

In young animals (including pups), DHA is obtained from milk and is synthesised from certain n3PUFAs for a limited period after weaning (1). Dietary DHA can be found in fish oil but also in some other foods, including eggs (9).

DHA deficiency in pregnant and lactating bitches may affect brain and visual development of their puppies (1). n3PUFA deficiencies from dog food are rare but the nutrition of a bitch during pregnancy and nursing is imperative to the cognition of its litter.

Diets fortified with fish oils containing high levels of DHA improved the learning capability of puppies compared to those fed low-level DHA fish oil (10).

(The ‘high-level DHA fish oil’ was also richer in certain amino acids and vitamin E, so the effect may have been combined)

Aging dogs

The cognitive ability of dogs reduces with age similarly to humans. Part of this decline is a result of prolonged oxidative damage. Enrichment of food with anti-oxidants has proven to reduce cognitive decline in dogs’ overtime (11,12).

Evaluation of ‘dietary doggy dementia solutions’

There is a commercially available anti-oxidant fortified diet (Prescription diet® Canine b/d®, Hills Pet Nutrition, Topeka, KS). The brain-food is also enriched with Omega-3 fatty acids and is designed to reduce cognitive decline in aging dogs. The effectiveness of this diet and similar experimentally prepared ones has been proven (13). So they must be on to something!

A supplement containing anti-oxidants, fatty acids (including DHA) and other compounds has shown some benefit in the alleviation of behaviours associated with cognitive decline in dogs (Aktivait, VetPlus Ltd., Lytham St Anne’s, UK) (14).

Elderly dogs have also demonstrated improved cognitive function when diets were supplemented with medium-chain triglycerides (97% caprylic acid and 3% capric acid), which provide an alternative energy source for brain cells (15). — Coconut oil is a good source of caprylic acid and capric acid, which may be a beneficial fat for dogs.

The take home message:

Behaviours associated with aggression and stress in dogs may be partly managed through nutrition. Tryptophan supplementation can promote serotonin production. This ‘feel-good hormone’ positively impacts behaviour. Increasing the ratio of tryptophan relative to other large neural amino acids is important for uptake into the brain. However, low protein diets should be treated with caution as they may have other detrimental effects in dogs. Tyrosine is another important precursor involved in stress-related neurotransmission. High quality ingredients with highly ‘bioavailable’ nutrients may promote normal behaviour.

Fatty acids including DHA may improve behaviour as well as cognitive function. This is vital in developing puppies and aging dogs that suffer from cognitive dysfunction. Anti-oxidants offer protection from cognitive dysfunction.

We must not forget that negative behaviour and cognition can have a negative impact on animal welfare.


1.Bosch, G., Beerda, B., Hendriks, W.H., Van der Poel, A.F.B. and Verstegen, M.W.A., 2007. Impact of nutrition on canine behavior: current status and possible mechanisms. Nutrition research reviews, 20(2), pp.180–194.

2. DE Napoli, J.S., Dodman, N.H., Shuster, L., Rand, W.M. and Gross, K.L., 2000. Effect of dietary protein content and tryptophan supplementation on dominance aggression, territorial aggression, and hyperactivity in dogs. Journal of the American Veterinary Medical Association, 217(4), pp.504–508.

3. Kato, M., Miyaji, K., Ohtani, N. and Ohta, M., 2012. Effects of prescription diet on dealing with stressful situations and performance of anxiety-related behaviors in privately owned anxious dogs. Journal of Veterinary Behavior: Clinical Applications and Research, 7(1), pp.21–26.

4. National Research Council, 2006. Nutrient requirements of dogs and cats. pp.128–129. National Academies Press.

5. Bednar, G.E., Murray, S.M., Patil, A.R., Flickinger, E.A., Merchen, N.R. and Fahey Jr, G.C., 2000. Selected animal and plant protein sources affect nutrient digestibility and fecal characteristics of ileally cannulated dogs. Archives of Animal Nutrition, 53(2), pp.127–140.

6. Hennessy, M.B., Voith, V.L., Hawke, J.L., Young, T.L., Centrone, J., McDowell, A.L., Linden, F. and Davenport, G.M., 2002. Effects of a program of human interaction and alterations in diet composition on activity of the hypothalamic-pituitary-adrenal axis in dogs housed in a public animal shelter. Journal of the American Veterinary Medical Association, 221(1), pp.65–91.

7. Hennessy, M.B., Voith, V.L., Young, T.L., Hawke, J.L., Centrone, J., McDowell, A.L., Linden, F. and Davenport, G.M., 2002. Exploring human interaction and diet effects on the behavior of dogs in a public animal shelter. Journal of Applied Animal Welfare Science, 5(4), pp.253–273.

8. Re, S., Zanoletti, M. and Emanuele, E., 2008. Aggressive dogs are characterized by low omega-3 polyunsaturated fatty acid status. Veterinary research communications, 32(3), pp.225–230.

9. Hill’s Pet Nutrition. (2017). What DHA is and What it Means for Your Pet’s Diet | Hill’s Pet. [online] Available at: [Accessed 3 Sep. 2017].

10. Zicker, S.C., Jewell, D.E., Yamka, R.M. and Milgram, N.W., 2012. Evaluation of cognitive learning, memory, psychomotor, immunologic, and retinal functions in healthy puppies fed foods fortified with docosahexaenoic acid–rich fish oil from 8 to 52 weeks of age. Journal of the American Veterinary Medical Association, 241(5), pp.583–594.

11. Cotman, C.W., Head, E., Muggenburg, B.A., Zicker, S. and Milgram, N.W., 2002. Brain aging in the canine: a diet enriched in antioxidants reduces cognitive dysfunction. Neurobiology of aging, 23(5), pp.809–818.

12. Milgram, N.W., Head, E., Zicker, S.C., Ikeda-Douglas, C.J., Murphey, H., Muggenburg, B., Siwak, C., Tapp, D. and Cotman, C.W., 2005. Learning ability in aged beagle dogs is preserved by behavioral enrichment and dietary fortification: a two-year longitudinal study. Neurobiology of aging, 26(1), pp.77–90.

13. Landsberg, G., 2005. Therapeutic agents for the treatment of cognitive dysfunction syndrome in senior dogs. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 29(3), pp.471–479.

14. Heath, S.E., Barabas, S. and Craze, P.G., 2007. Nutritional supplementation in cases of canine cognitive dysfunction — A clinical trial. Applied Animal Behaviour Science, 105(4), pp.284–296.

15. Manteca, X., 2011. Nutrition and behavior in senior dogs. Topics in companion animal medicine, 26(1), pp.33–36.

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