Okay so this is a question for anyone who comes across this, I breed and sell rabbits, I usually keep them from birth until they are a month old, so should I write their weight down from that age? Or just tell whoever takes the baby to weigh them in 5 months?
The weights on a pedigree are largely for the purposes of registering a purebred rabbit in the ARBA studbook: to be registered, the rabbit must have a 3-generation pedigree that includes the name/tattoo, variety and senior weight of each ancestor. Senior weights are also, to a lesser degree, useful to some breeders because they can give an idea of the size the line of rabbits can be expected to grow. So, weights on a pedigree are not critical for mixed-breed meat or pet rabbits, though they can be interesting to a breeder if they are accurate senior weights.
A rabbit being registered will be weighed by the ARBA Registrar at the time of registration, so there really doesn't need to be a weight for the rabbit on its own pedigree. But the senior weights of its
ancestors are important on a purebred's pedigree, since that allows future owners to register their rabbits.
Having the weight of a rabbit at a month of age, or even 5 months, isn't necessarily helpful, so leaving a blank for the weight of a junior you're selling makes sense. Depending on the breed, rabbits are considered seniors at 6 months (the smaller 4-class breeds) or 8 months (larger 6-class breeds, which includes most meat rabbit breeds). The new owner can fill in the senior weight when the time comes. Note that a rabbit who is already at senior weight at 6months can be registered at that time, even though it's not 8 months old yet. If the rabbit is registered, the registration weight will become the "official" weight which should appear on all pedigrees from then on, whether or not the rabbit gains more weight after that.
Because I like to keep track of the size of my stock, I usually wait until the rabbits are their full adult weight to register them, even though many of my rabbits reach the senior minimum by 6 months. If one of my breeders is not registered (because it is not a recognized variety, for example), I put the most accurate senior weight I have on the pedigree of its offspring.
Another reason to leave the weight blank on a rabbit's own pedigree is that when the rabbit is registered, either the pedigree needs to be copied out in full by hand on the registration papers, or a printed copy of the pedigree can be submitted. However, if it is a printed copy, there can be
no corrections anywhere...so if there's a junior/incorrect weight printed there, that pedigree will not work for submission.
A side note here is that each breed has its own senior weight minimum, and some breeds have senior weight maximums. The rabbit being registered needs to fall within those limits, but its ancestors do not; a rabbit can still be registered if it has ancestor/ancestors that are heavier or lighter than the standard, or if they are unrecognized colors, as long as they are all of the same breed (aka purebred).