Not sure if this has already been posted in the past... might be useful for some in the future.

I think there are still many(my vet practise owner included) who think puppies can benefit from colostrum for weeks but research shows the time is actually very very short.

Very useful to know in case of a lost bitch or if bitch refuses to look after the young -one would have to milk the bitch(or hold them down) for very short time to give benefit of antibodies.

I have little random discussions with one vet at the practise and have discussed giving newborns serum and my vet said it can be done if the worst was to happen and bitch died.
This was using another of my dogs as donor as would have been exposed to things in our environment, where the pups would be brought in to.

https://www.puppyculture.com/phone/fading-puppy-syndrome.html

Not for nothing is this called 'first milk'.   As far as I'm aware, and have always been aware, the colostrum that provides the natural immunity, or should, is just the first milk.  And if it's felt the puppies didn't take the first milk, an interim external vaccination against the two main diseases, Parvo and Lepto, would be given as early as 6 weeks.