Hi
here is link to a lab that does the testing (your vet cannot do the actually test so sends the blood away)
http://www.cslabs.co.uk/reproduction%20female%20page.htm#ovulationAnd this is the way to read the values given
Progesterone (quantitative)
A blood sample should be taken about day 7 post vulval bleeding. In most bitches the progesterone concentration will be <3 nmol/L indicating that ovulation has not occurred. If the progesterone level is above 6 nmol/L, ovulation has occurred and depending on the actual level we will advise when to sample again if required.
Interpretation
Progesterone <1.0 - 3.0 nmol/L Ovulation has not occurred, resample 3 -4 days
Progesterone >6 nmol/L Ovulation has occurred, resample again if required
Progesterone 16 - 20 nmol/L Mate within 33 - 57 hours
Progesterone 20 - 38 nmol/L Mate within 9 - 33 hours
Progesterone >38 nmol/L Mate within 9 hours
This is a far more acurate way of determing opitum mating times than the standard premate test (done by reading a colour against a chart), always been successful on my bitches . Good luck