Chronic enteropathy in a young adult dog with negative parasitology and normal bloodwork is one of the more frustrating clinical pictures because the underlying differentials are diet-responsive, immunosuppressive-responsive, or antibiotic-responsive, and you usually find out which by sequentially trialling them.

Your vet's recommendation to move to a hydrolyzed protein diet is the correct next step under current ACVIM guidelines (Cerquetella et al., 2010; Jergens, 2012). A few practical notes:

• Hydrolyzed diets work for the majority of food-responsive enteropathy cases. Best evidence is for Royal Canin Hypoallergenic HP, Hill’s z/d Ultra, Purina HA. Roughly 60-70% of dogs with chronic GI signs respond within 8-12 weeks of strict elimination.
• Strict means strict. No other food, no flavored heartworm meds, no rawhide, no treats outside the diet. One contamination resets the clock. This is the #1 reason owners think a hydrolyzed trial “didn’t work” — the trial wasn’t actually clean.
• Probiotic add-on can help. Specifically multi-strain veterinary-grade probiotics (FortiFlora, Visbiome Vet, Proviable-DC) have RCT support for stool quality in chronic enteropathy. Not a substitute for the diet trial, but a useful adjunct.
• If 8-12 weeks of strict hydrolyzed shows no response, the next workup is typically GI biopsy via endoscopy to differentiate IBD subtypes, or empirical immunosuppression trial (prednisone, sometimes with cyclosporine). That’s a bigger decision — $1,500-2,500 for endoscopy — but it’s how you avoid medicating something that's actually a structural problem.

Worth checking before the hydrolyzed trial: a basic GI workup that’s sometimes skipped — cobalamin/B12, folate, TLI (for EPI), and a baseline serum bile acids if any liver enzyme is borderline. Cheap and they redirect the diagnostic path completely if abnormal.