My ACD is 3 years old and I've seen the olive oil tip many times in various discussions on dog and pet boards online. I've also heard that you shouldn't give it to them every day. I'm not sure why but he has never had a problem with dull coat. Always plenty of oils to keep it nice. He's just itchy.
As for shampooing. I usually use a gentle or oatmeal based dog shampoo. I've used a good conditioner on a few times and I always rinse him well. He hates baths so I have a high powered sprayer I use so he isn't in a tub of water. I know, weird huh? He hates baths but cattle dogs generally love water and are built for swimming with their thick coats and webbed toes.
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Snakes, Jeeps, Dragons, Nature, & Knives.. Makes my world go-round!