Breastmilk auto-expression and self-suckling in a Zoo-bred Japanese macaque (Macaca fuscata)

Breastmilk auto-expression, also called “self-suckling", is a rarely observed behaviour in mammals. We present detailed observations of this behaviour in a Zoo-bred Japanese macaque (Macaca fuscata), in the context of extended nursing by the offspring. This is in contrast to prior reports of self-suckling in primates, which were associated with the death of the infant. We followed mother Miya (MI) and infant Shoyo (BB) for the first two years of the infant’s life, documenting changes in his activity budget during development. After first observing that MI was consuming her own breastmilk independent of nursing bouts with BB, we began measuring instances of this behaviour within MI’s activity budget. We describe this self-suckling behaviour in the context of ongoing nursing interactions and a normal oestrus cycle and speculate whether this behaviour is the cause or a consequence of MI’s failure to become pregnant after BB’s birth.