Being very careful with the diet and minimizing stress are the most important things with a newly weaned rabbit. With new baby rabbits it's important to always stick with the exact same food they are used to and what their gut is used to, provided the diet isn't causing serious digestive illness. So you want to be feeding the exact same type and brand of pellets, the same hay, the same foods, except for any sugary high starch treats. Those should be eliminated completely to minimize the chances of gut upset occurring.
Baby rabbit diet
Then minimizing things that stress the baby, giving it time to settle in and get used to it's new home. If it's a really nervy bun, no handling unless absolutely necessary, providing a calm quite area that doesn't stress it, providing hidey holes. If it seems to be well adapted, curious, and comfortable with people, then you don't have to worry so much about it having trouble settling in, but be mindful of things that might seem to stress the baby at all.
If the baby wasn't used to alfalfa hay in it's previous home, I wouldn't feed the alfalfa hay and would stick with whatever grass hay it was fed there. If it was fed alfalfa hay in it's previous home, I would also offer some type of grass hay in addition to the alfalfa, then in a couple of weeks gradually start fazing out the alfalfa hay. If the baby is already getting an alfalfa based pellet, my opinion is there's no need for it to also have alfalfa hay. It can make for too rich of a diet leading to excess cecotropes and possibly bladder issues(excess calcium), and also can make for a very picky bun that doesn't want to transition to a grass hay when it becomes an adult and no longer should have alfalfa.
In a couple of weeks if the baby is doing well, then I would start slowly transitioning it onto whatever type of healthy junior pellet you intend to normally feed. And after the pellet transition, usually leafy greens can be very slowly and gradually tested out(unless the baby is sensitive and having issues), starting with a very small amount and one at a time if there or no signs of digestive upset.
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