Lentils are great in small quantities. However, if your uro is not eating much of anything else, I wouldn't give lentils until he starts eating his greens well. If he eats nothing but lentils, he's likely to dehydrate himself. Just keep offering a good variety of healthy greens and shredded veggies - he won't starve himself if he's healthy. Try a few mashed up green peas and some shredded butternut squash. You can also pull apart a yellow dandelion head (free of any pesticides) and mix that in. All those things tend to be very, very attractive to uros.
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Torey
Eugene, Oregon, USA
1.2 Saharan Uros (Joe, Arthur, and Hitch)
3.0 Mali Uros (Spike, Turtle, and Tank)
1.1 Ornate Uros (Scuttlebutt and Shazzbot)
1.2 Collared Lizards (Ripcord, Thiamine, and Riboflavin)
1.0 Green Anoles (Sprocket)
1.1 Housecats (Roscolux and Jenny)