SPECIES-SPECIFIC FEATURES OF ESTROUS DEVELOPMENT AND BLASTOGENESIS INDOMESTIC CANINE SPECIES

The reproductive physiology of taxonomically closely related species i s usually very similar. The main difference in the reproduction of the dog and fox is the length of the different phases of the oestrous cyc le. 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 abo ut 1 week in the dog. The profiles of sex steroid concentrations in pl asma during oestrus and pregnancy are similar and the luteal phase in non-pregnant animals is prolonged, progesterone concentrations reachin g a maximum by 15-30 days after the luteinizing hormone (LH) peak in t he dog, by 10-20 days in the blue fox and by 5-15 days in the silver f ox. The duration from LH surge to ovulation is about the same in the d og and fox, but thereafter the oocytes and early embryos develop faste r in foxes than in the dog. The tubal transport time is 4-6 days in th e silver fox, embryos entering the uterus at the 4-16-cell stage. In t he blue fox the oocytes remain in the oviducts for 8-10 days, developi ng 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. The gestation length relative to the LH peak can be calculated to be 56 d ays in the blue fox and about 54 days in the silver fox.