Observations on the oestrous cycle and gestation period of the Greater Bilby, Macrotis lagotis (Reid) (Marsupialia: Thylacomyidae).

Abstract

Observations were made of the oestrous cycle and gestation period of the Greater Bilby, Macrotis lagotis. Seventeen animals (12 females, five males) were used in this study. Smears were taken daily from the urogenital sinus in order to monitor the oesirous cycle. Two stages were recognised in the cycle. The first stage was characterised by the appearance in smears of greater than 80% cornified epithelial cells and very few polymorphonuclear leucocytes. The mean duration of this stage was 4 days (range: 2-11 days). Stage 2 was characterised by a lower percentage of cornified cells (generally <65%) and a greater abundance of Ieucocytes. Its mean duration was 17 days (range: 7-30 days). Histological evidence of ovulation and nocturnal observations of sexual activity occurring during Stage I of the cycle indicated that oestrus occurred during this period of intense urogenital cornification. The length of the oestrous cycle was measured as the period between two consecutive stages of intense cornification. Cycles were detected in only six of 10 animals smeared. The cycle length averaged 21 days (range: 12-37 days; n = 14). Gestation length was measured as the interval between parturition and the first day of the preceding period of intense cornification. Gestation length averaged 14 days (range: 13-16 days; n = 4).