It may be helpful to add your location. We use a local brand here, but I don't think you'd be easily able to find it if you are in the States.
The way you are describing it sounds like there may be other things added in the pellets. Is it a blend you are feeding? Are your rabbits eating around the pellets to get whatever is mixed in with the pellets? As a very general statement, most blends like the below are not all too great for rabbits.
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You'll be better off with plain pellets, shown below, and giving rabbit-safe treats as needed.
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As for mothers and kits; we switch to a "breeder blend" pellet, which has a higher percentage of protein in it. The kits nibble on them as they are weaning. As they age and are getting closer to leave the mother, we'll gradually mix in the standard feed with a slightly lower protein content. If the doe isn't regaining condition, we keep the breeder blend and switch the kits off of it when they are separated from the mother entirely. You won't want to immediately switch to another pellet when your kits begin eating. They'll continue to get nutrients from the mother and are going to have serious digestive issues with a drastic change of food. This is why weaning can sometimes result in diarrhoea. As soon as the doe is bred is when we begin the pellet transition for her.
If my memory is correct, alfalfa-based pellets are higher in calories and lower in fibre than timothy-based pellets. Those calories will be important in the growth phase, but make sure there is still plenty of fibre in their diet (hay, cornstalks, etc.). Those calories will also make them accumulate fat, though, if you're not careful and overfeed. This being said, we don't specifically switch between types of hays for the pellets here.