In the last decades, adverse food reactions have increased considerably in dogs and cats. In this study we report on the possible onset of food intolerances symptoms, including otitis, diarrhoea, generalised anxiety, and dermatitis in a cohort of 8 dogs consuming commercial diets. All dogs received an organic chicken-based diet for 15 days. We performed analysis of blood biochemical parameters, kibble composition, and oxytetracycline (OTC) serum concentration before and after 15 days of organic chicken-based diet supplementation. We hypothesised that a chronic intake of contaminated food enhanced by the presence of nanoparticle aggregates might be at the base of the onset of pharmacologic or idiopathic food intolerances. At the end of the evaluation period, an overall significant reduction of otitis, diarrhoea, generalised anxiety, and dermatitis was observed. Biochemical analyses indicate a significant increase in the alkaline phosphatase, from 41 to 52.5 U/L, after 15 days (••p <0.01), while a significant decrease in Gamma-glutamyl transferase and urea, from 9.37 to 6.25 U/L and from 32.13 ± 8.72 to 22.13 ± 7.8 mg/dL, respectively, was observed (•p <0.05). A significant decrease, from 0.22 to 0.02 μg/mL, in mean OTC serum concentration was also observed (••p <0.01). Composition analysis revealed the presence of OTC, calcium, aluminium, silicon, and phosphorous nanoparticle aggregates. Further research on a wider sample size would help to confirm the hypothesis proposed here.