This section is from the book "The Dogs Of Great Britain, America, And Other Countries. Their Breeding, Training, and Management in Health and Disease", by John Henry Walsh (Stonehenge). Also available from Amazon: The Dogs Of Great Britain, America And Other Countries.
Until weaned, the management of dogs does not require much care beyond the feeding of the mother, and the necessity for removing a part when the numbers are too great for her strength to support. For the first fortnight, at least, puppies are entirely dependent upon the milk of their dam or a foster-nurse, unless they are brought up by hand, which is a most troublesome office, and attended also with considerable risk. Sometimes, however, the bitch produces twelve, fourteen, or even sixteen whelps, and these being far beyond her powers to suckle properly, either the weak ones die off, or the whole are impoverished, and rendered small and puny. It is better, therefore, especially when size and strength are objects to the breeder, to destroy a part of the litter, when there are more than five or six in the greyhound, or seven or eight in the hound or other dog of that size. In toy dogs a small size is sometimes a desideratum, and with them, if the strength of the dam is equal to the dram, which it seldom is, almost any num. ber may be kept on her.
For the first three or four days, the bitch will be able to suckle her whole litter; but if there are more puppies than she has good teats, that is, teats with milk in them, the weak ones are starved, unless the strong ones are kept away in order to allow them access, so as to fill themselves in their turn. To manage this, a covered basket, lined with wool if the weather 187 is at all cold, should be provided; and in this one-third or one half of the puppies should be kept, close to the mother, to prevent either from being uneasy, with the lid fastened down or she will take them out in her mouth. Every two or three hours a fresh lot should be exchanged for those in the basket, first letting them fill themselves, when they will go to sleep and remain contented for the time fixed above, thus allowing each lot in its turn to fill itself regularly. At the end of ten days, by introducing a little sweetened cow's milk on the end of the finger into their mouths, and dipping their noses in a saucer containing it, they learn to lap. After this there will be little difficulty in rearing even a dozen; but they will not, however carefully they may be fed, be as large as if only a small number were left on her.
Therefore greyhound breeders limit their litters to five, six, or at most seven; destroying the remainder, or rearing them with a foster-nurse.