My chickens liked to dig for slugs. They like digging and scratching up stuff themselves. Don't worry about it. Chickens eat what their body needs. For 3 years I had a Silkie that wouldn't eat tomatoes until our new Ameraucana went for it and now she eats tomatoes 3 years later! Chickens are wary creatures and take time to adjust to a particular meal or food. After the slugs and snails were all pretty much eradicated by the hens they suddenly decided Earwigs were a good substitute and they never touched them before! Only one of our hens chases Japanese Beetles while the others ignore them. Who knows what makes chicken food tasty - a color, a texture, a taste, a smell, a shape ???