Introduction Escherichia coli is the most common pathogen isolated from the urine of dogs with urinary tract infections (UTIs). While there are many studies in humans investigating the potential for the prevention of UTIs by dietary consumption of cranberry, few analogous studies have been carried out in dogs. Material and Methods Eight dogs, four male and four female, were successively fed two diets, first a control without cranberry, and then the second diet containing cranberry extracts. Naturally excreted urine was collected on the tenth day after the start of each diet for 24 h and used for bacterial growth. Madin-Darby canine kidney cell adherence by the uropathogenic E. coli G1473 strain expressing type 1 pili and positive for P pili and haemolysin gene markers was quantified after growth in urine samples. Results Significant reductions in bacterial adherence to MDCK cells (from −16.5 to −73.4%, P < 0.05) were observed in the four females but not in the males after consumption of the cranberry extracts compared to the same animals consuming the control diet. Conclusion Dietary supplementation with cranberry may provide some degree of protection to female dogs against adhesion of uropathogenic E. coli to urinary epithelial cells.