These tips are mostly for Holland Lops; some breeds are more hardy and can handle different things, but Hollands are very fragile in their digestive system, so they need a little bit more TLC than some other breeds.
There are many reasons why someone might need to wean a baby bunny early. I have done it myself, only once, when the baby was getting bitten and picked on by its siblings. However, there is no excuse for selling a baby bunny younger than 7 weeks, besides making more money. I'll be the first to admit, bunnies are at their cutest at about 4 weeks old. Some breeders try to sell them at this time so they can make more money and won't get stuck with a 8wk or older baby they can't sell. Personally, I choose to keep the rabbit as long as possible until it finds the perfect home, than to risk its health.
So many people have emailed or messaged me about problems with their rabbit...and soon during the conversation I find out that rabbit is only 4-5 weeks old. This is an incredibly fragile time in the rabbit's life. Babies usually don't start eating pellets until 3-4 weeks old, and it can take 1-2 weeks for their bodies to properly adjust to it. When their bodies are already going through the stress of adjusting to other food besides mom's milk, and then it gets sold to a new home and has to cope with the stress from that, it can be fatal in most cases.
However, there are many ways you can protect your baby bunny from too much stress, and keep it as healthy as possible. Here are some tips.
Hay, hay, hay -
Hay is super important for all rabbits, but it's vital for baby bunnies that are just starting to eat pellets or switching homes, or doing anything stressful. Hay is full of fiber, and it keeps the poop regular and the gut healthy. The best types of hay are Timothy hay and Orchard Grass hay. Alfalfa hay is sometimes recommended for rabbits that are under 6mos, but it has been linked to kidney and liver issues because it is really high in protein, and doesn't have enough fiber to balance it out. Because fiber is the main reason why hay is fed, alfalfa hay should just be avoided.
NO fruits or veggies -
Fruits and veggies should be avoided for all rabbits until 6mos old, but feeding it to babies whose bellies are just starting to get used to pellets and stress can be fatal.
Oats "dry up" diarrhea and soft poop, which is common for babies that are just starting to eat pellets, changing homes, or just enduring any stress. Never use quick oats; the best oats to use are old fashioned, rolled oats. I feed my babies two teaspoons of oats with their pellets twice a week, and this helps their poop stay solid.
Minimal household stress -
If you can, keep the new area where the baby lives as stress-free and as quiet as possible for a couple weeks after bringing your 4-5 week old Holland home. Don't introduce your baby to the household pets yet, and keep the kids from bothering the rabbit too much. Minimal handling is okay, but don't go overboard, and if your rabbit seems stressed, leave him in the cage.
Same pellets as breeder -
Make sure the breeder gives you the pellets the baby bunny had been eating previously, and keep the baby on these pellets for several days. After about three days, mix your pellets with the original pellets half and half until the rest of the original pellets are gone.
Probiotics or Enzymes -
Probiotics are extremely helpful in keeping your baby bunny from getting sick from stress. You can use human probiotics that can be purchased at any vitamin store, or you can use animal probiotics that can be purchased online or at a feed store/Tractor Supply. My favorite type of probiotics to use are AcidPak 4Way, which I bought online at bunnyrabbit.com.