My colleague doesn't take her two dogs for a walk, what should I say?

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my friend has two border collies aged 6(ish). THey are kept outside (they have a large shed style 'house' out there) until night time when they come in. They are both overweight. She has a massive garden but openly admits she nevers walks them. Doesn't have the time. They are lovely dogs and I cannot help thinking this is wrong. We are work colleagues but not friends as such though we do get along well. I did express my surprise when she told me they don't get walked. What would you do?

RedwingWinter - thanks for the informative link. I can now read this link and say (after the good advice from posters in the doghouse) that walking these dogs 50min a day, five days a week is clearly not quite enough (even though they are stuck in a special isolated compound for 23 hours)...could I suggest that perhaps if they hired the walker for a couple of walks the weekend the dogs would no longer exhibit signs of distress??