The first few months of your puppy’s development are crucial! Your puppy is just a baby and its delicate skeletal frame has not yet set into position. Bone and muscle growth are very important during this stage of their life. Caution is needed.
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A general rule of thumb for Golden pups is only taking them for the same duration walk as their age in weeks. Example: a 20 week old puppy should be out for 20 minutes once a day and I would probably break that up to two 10 minute walks. Work up exercise levels slowly; but also keep in mind that some dogs will keep going and not know when to quit.
For the first 18 months, be very careful when exercising your puppy! You should not overexert them. Running long distances and for long periods of time, or letting your puppy do full flights of stairs should be avoided. If necessary, carry your puppy up and down stairs for as long as possible. Once they are too heavy to carry, teach them to take the stairs very slowly but only if the stairs are absolutely necessary. A few stairs to get in and out of the house are not as much of a concern as long as your pup does not try to “fly” or jump over them.