The effect of pregnancy on the interval between one oestrus and the next in the tammar wallaby, Macropus eugenii.

In females mated to vasectomized males the interval between oestrous periods was 30.6 +/- 1.17 (s.d.) days but when mated to intact males and pregnancy intervened, it was 29. +/- 1.26 days (P less than 0.0025). After removal of pouch young, females carrying diapausing blastocysts gave birth 26.2 days later and came into oestrus 26.4 +/- 0.57 (s.d.) days later. When post-partum fertilization was prevented, removal of pouch young was followed by oestrus 30.4 +/- 0.99 days later (P less than 0.0005). These results indicate an influence of the conceptus upon the oestrous cycle of Macropus eugenii.