Timing the mating of dogs on the basis of blood progesterone concentration.

The optimal time for mating bitches was determined by measuring the progesterone concentration in peripheral blood three times a week after the start of vulval bleeding. Of 104 bitches with reduced fertility 81 (78 per cent) became pregnant and of 112 bitches with normal fertility 105 (94 per cent) became pregnant. Of 121 bitches mated once, 102 (84 per cent) became pregnant, and of 95 bitches mated more than once, 84 (88 per cent) became pregnant. The mean (+/- sd) interval between the start of vulval bleeding and the optimal time for mating in 88 bitches was 11.8 +/- 3.1 days. The blood progesterone concentration appears to be an excellent indicator of the best time for mating, particularly in bitches with reduced fertility.