my friends bitch was mated on Friday, saturday and sunday last week. Unfortnately she escaped and got  to  7 month old puppy yesterday  and they had tied before she could be recaptured. Thanks to a recent thread we know about dna testing to see who the father is. they are the same breed and not closely related  so friend is reluctant to have the injection.
does anyone know if a 7 month old pup is likely to be fertile? (I am guessing if he can mate he should be fertile) this mating was  on day 19, the other matings were on 12, 13, and 14. the stud lost interest after that and she wouldn't stand so is  a mating on day 19 likely to produce puppies?    and if so is the widely spaced mating likely to cause problems with  puppies from the later mating being much smaller than from the first matings?

Yes a 7 months old male would be fertile.

The foetuses do not implant until about the third week so the spacing of matings should make no difference.

A bitch will only have fertilise eggs for around 2 or 3 days at most.

A dos semen can survive for about a week, but be most viable for about 4 days.

Some bitches will stand just a day or two before ovulation (many won't until after ovulation or until the eggs are ripe, ditto the males), but the eggs won't be ripe for two days.  Standign for a week (12th to 19th day in this case) is therefore not uncommon.

An inexperienced male may try to mate a bitch at any point in the season, if the bitch will allow, some experienced bitches are little tarts and may stand for prolonged periods (from before ovulation to well past the fertile period).

So if the other (experienced I am surmising) stud lost interest after day 14 I would tend to think she had gone over, and would not be fertile by day 19. 

On the other hand depending on age and stamina, maybe he was tiring after three days, and she had allowed mating before or at ovulation, in that case there may still have been fertilizeable eggs by day 19.

Thank God for the availability of DNA testing.  It is likely that it will confirm that all the pups are from the first stud.

Sorry for the delay in replying spent the weekend at Crufts. The bitch has definitely finished her  season now so it sounds like she may be lucky and not have pups sired by the second dog. As you say, thank heavens for DNA testing.