Effect of weaning time on the growth rate and food intake of the spiny mouse pup

The spiny mouse Acomys cahirinus produces well-developed pups although it is a relatively small mammal (45 g). We envisioned two opposing hypotheses on the effect of early weaning on the growth rate of pups. The first predicts little effect since the increase in energy intake of dams above non-reproducing females is relatively low, suggesting that pups consume a large portion of their energy as solid food, and the pups are very well developed at birth. The second predicts a substantial effect since the 'index of precociality', that is the energy intake for maintenance of a pup as a proportion of that predicted for a rodent of its body mass, falls within values for altricial rodents, suggesting an extended maternal dependence of the young. To test these hypotheses, we measured the growth rate and food intake of pups weaned after either 7, 14, 21 or 28 days. Only three of 12 pups weaned after 7 days survived and, consequently, the latter hypothesis was supported. All pups weaned at 14-28 days survived. There was a significant decrease in growth rate during the first day after weaning in pups weaned at 7, 14 and 21 days but not after 28 days, suggesting that pups did not require parental care by day 28. Peak growth rate in pups weaned at 14 days occurred in the second week but occurred in the third week in pups weaned at 21 and 28 days. In spite of these differences, pups in all treatments had similar body mass at 64 days, indicating compensatory growth. We concluded that pups of A. cahirinus are precocial from a morphological aspect in that they are well developed at birth but altricial from a nutritional aspect in that they require extended maternal support.