Species-specific features of oestrous development and blastogenesis in domestic canine species.

The reproductive physiology of taxonomically closely related species is usually very similar. The main difference in the reproduction of the dog and fox is the length of the different phases of the oestrous cycle. Pro-oestrus and oestrus are longest in the dog: oestrus lasts 3-5 days in the blue fox and 1-3 days in the silver fox, compared with about 1 week in the dog. The profiles of sex steroid concentrations in plasma during oestrus and pregnancy are similar and the luteal phase in non-pregnant animals is prolonged, progesterone concentrations reaching a maximum by 15-30 days after the luteinizing hormone (LH) peak in the dog, by 10-20 days in the blue fox and by 5-15 days in the silver fox. The duration from LH surge to ovulation is about the same in the dog and fox, but thereafter the oocytes and early embryos develop faster in foxes than in the dog. The tubal transport time is 4-6 days in the silver fox, embryos entering the uterus at the 4-16-cell stage. In the blue fox the oocytes remain in the oviducts for 8-10 days, developing into the morula stage, whereas in the dog a still longer oviductal phase results in embryos that are at the compact morula or blastocyst stage when entering the uterus. The preimplantation period is about 1 week in the dog and the blue fox, but 9-10 days in the silver fox.(ABSTRACT TRUNCATED AT 250 WORDS)