The young of domestic cats generally start to move onto solid foods at around 30 days (Turner & Bateson, 2000). Changes in the kittens' gut morphology and digestive biochemistry at the time of weaning, defined as the time when dietary dependence on the mother changes most rapidly, probably have the same pattern as those tound in the rat. The lining of the small intestine of the rat is relatively smooth before weaning, but after weaning the villi rapidly proliferate (Herbst & Sunshine, 1969). In addition, the enzyme lactase, which is used for digesting milk sugar, is replaced by sucrase, which is used for digesting the sugars in solid food (Henning, 1985; Lund & Smith, 1987). The timing of the changes in the digestive system are closely linked to the various factors that affect the timing of weaning (Gomendio et al., 1995). In the cat, if the mother is small, under-nourished or is burdened with a large litter, the rates of increase in weights of her kittens slow down prior to weaning, but increase again in the days after the kittens take their first solid food (Bateson & Young, 1981; Deag et al., 1987). In such cases the mother has probably reached the limit of her ability to supply sufficient energy from her milk for the continued growth of her kittens, but rapid gain in weight resumes as soon as the kittens are able to process solid food.
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