Yes, I have heard that too but I have no idea why they say it! All the grays I've had LOVED juicy fruits and oranges are one of their favorites. Mine get oranges once a week almost all year round but, on occasion [as when they are on sale or cheap because they are in season
], they also get tangelos, tangerines and ruby grapefruit. I've been doing this for over 20 years and never noticed any harmful effects...