The oestrous cycle of female Rattus (Mastomys) natalensis (Smith) as observed in the laboratory



  • 1 The average period between successive oestrous cycles for Mastomys females has been found to be 8.8±0.4 days.
  • 2 Pro- and met-oestrous periods were found to last an average period of 1.9±0.15 days respectively.
  • 3 The mean age of females on the perforation of the vulva was 76±5.9 days and their mean age at the first oestrous was 104±9.2 days. The age of females at the birth of their first litters was about 130 days.
  • 4 The mean length of the gestation period was 23±10.7 days. Bloodstained vaginal smears were noticed on about the fifteenth day of pregnancy in thirteen out of seventeen cases.
  • 5 Post-partum oestrous occurred regularly during lactation, the first on the average occurring 2.6±0.52 days after the birth of the litter. Oestrous recurred regularly about every six or seven days thereafter if the females did not become pregnant.
  • 6 Some females conceived at the first post-partum oestrous and produced litters twenty-three or so days after the birth of the previous litter.
  • 7 Fairly lengthy periods of anoestrous occurred (37.9±4.98 days) followed by cycles of longer duration than normal. 0.53 of the total life-times of all the females was spent in anoestrous though only ten periods of anoestrous were observed while the twenty-five females exhibited eighty-two oestrous cycles.