Hey! Glad your bun finally had her babies! Its normal to have a few different sizes in a litter of that amount. You can tell if they are full but looking at their tummies. A well fed bun will have a tight, stretched looking tummy, with little to no wrinkles between its tummy and legs. A hungry bun will have a sunken in tummy with folds of loose skin. Here is a few photos.
This baby is one of 3 and very very well fed! You can see her huge fat round tummy and tight skin.
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Here's another picture of a full tummy from the side.
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The top 2 babies in this photo are healthy and well. The bottom one was a runt and did not survive. You can tell he's a lighter color, skinnier, and not thriving.
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I've found the most you can do is give mama plenty of food, water, and nutrients she needs to produce enough milk. I give my pregnant buns unlimited pellets and hay, and about a tablespoon of calf manna. The calf manna(comes from feed stores like Tractor Supply) boosts her milk production and makes her milk richer with nutrients the babies need to live.