
On the other hand in breeds that don't normally whelp really early day 64 is not unusual if the bitch was mated early.
I have had bitches in my medium size breed whelp from 58 days from single mating and up to 67 (4 days late) to a single mating, and to the first day of multiple matings.
Some bitch will mate as early s the LH surge (two days before ovulation) and some as late as 4 days after ovulation when the eggs are dying off.
Most bitches whelp 63days +/- a day from ovulation.
So your late mated bitch will appear to whelp early, and an early mated own appear to go over.
If your vet can do in-house progesterone testing a reading blow ovulation levels means the bitch is ready to whelp, more accurate is proper quantative testing but due to specialist labs doing the test the time lag may make it impractical.
http://www.peteducation.com/article.cfm?c=2+2109&aid=3201Toy breeds are a case where knowing what is normal for your breed is important, as some whelp early because the puppies are so cramped, this triggers whelping. Larger litters in most breeds tend to be earlier than small ones as the puppies help trigger whelping.