Frozen, raw salmon chunks. In 2kg (approx) packs.
Salmon is a great source of omega-3 fatty acids which support the immune system, may decrease inflammation, and can keep your dog's coat looking shiny and healthy. It's also a good protein source. In 1kg or 2kg bags (approx).
Feed as part of a raw, nutritionally balanced diet for working dogs. 
Disclaimer:  Dogs should be supervised at all times whilst feeding and always provide plenty of fresh water for your dog.