The mothers of eight litters of domestic cats, Felis catus, were given a rationed diet after the birth
of their kittens so that they received approximately 80% of the energy intake when given ad libitum food.
Rationing of the whole family was maintained until the end of the period in which the family were
observed. The subsequent play of the kittens was compared with that of litters of the same mothers when
the families were given ad libitum food. When the mothers received rationed food, their kittens played with
objects significantly more than when the mothers received ad libitum food. This was a specific effect and
was not due to a general increase in the activity of the rationed kittens. Over the first 18 days after birth
the extent to which mothers were unavailable to their kittens when rationed was strongly correlated with
the object play of their kittens 70-84 days after birth. While the kittens in the rationed condition were
well buffered from the effects of rationing, they nuzzled significantly more than those in the ad libitum
condition in apparent attempts to reach their mothers' nipples.