there is an indoor brand of pellet, brought out by Burgess. it has added vitamin D. its also very high in fibre (40%) so I think it might be the highest fibre pellet out there at the moment. but I'm not sure as I don't remember all of the fibres on rabbit pellets [emoji38] it is however more expensive and doesn't come in larger packets. so for those with a lot of rabbits, or wanting to save buying in bulk, its not an option sadly.
https://shop.burgesspetcare.com/rabbit/food/Excel-Indoor-Rabbit-Nuggets/62
I'm not too sure how much vitamins are, but tbh the indoor rabbit doesn't really have that much vitamin D more it would seem. but I fully raise my hands in the air as I don't really understand vitamins, and I am purely looking at numbers.
indoor burgess rabbit: Vitamin D3 (cholecalciferol)(3a671) 3,500 iu/kg
original burgess rabbit: Vitamin D3 (cholecalciferol) (E671) 2,000 iu/kg
it would seem per KG that it has 3500 iu (whatever that is lol) of vitamin D..but the thing is is that pellet makes up such a small amount of a rabbits diet, that I'm not entirely sure how beneficial it is. its going to take a long time to get to 1 KG of pellet with what most rabbits have. many have a tablespoon of pellet (if that). I doubt that its more than 5g for some pellets when it comes to weight. I just don't know how beneficial it would be with how little they actually have.
the link you gave is interesting Kelet, but I'd really like to see the study itself, like the data sheets, which doesn't seem to be linked back to. or I can't find it, just a reference. its just "a study" with no numbers or actual evidence. I'm not one to take what I read, I like actual facts. but I'm also very stubborn and skeptical
I will have to give it a read through later, and find the actual study to take a look at.
I know my parents cat is very interested in a lamp my dad has, its a bright UV bulb and he uses it for reading sometimes too. but I personally think that the cat is purely interested in it for the heat it admits, hence why we call it a little heat lamp. I'm not sure he's doing it that its good for him, as he only moves after its warmed up and is spitting out heat [emoji38]