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NUMBER OF MATINGS PER LITTER
In the mating of dogs most breeders agree that 2 or 3 matings are desired, although one is all that is necessary. It is good to breed 2 or 3 times for several reasons: to ensure the bitch's being served during the period of ovulation, which sometimes is difficult to ascertain; it gives the bitch the best opportunity to produce the largest number of puppies; and it gives the stud a chance to produce some good sperm if he has not been used for some time. It has been proved that if a stud is not used for a long period, the semen may lose much of its potency.
I don't advise breeding more than 4 or 5 days apart because of the possibility of conception at both breedings, and there will then be a premature puppy or two in a litter of normal healthy puppies.