We hypothesized that energy intake of lactating females is the main factor determining growth of the young and that use of maternal energy reserves is less important when food is available in abundance. We studied reproducing female common spiny mouse (Acomys cahirinus) offered millet seeds and water ad libitum. Females gave birth to 1 or 2 young, and growth rate was similar between litters of 1 infant and 2 infants combined. In addition, energy intake of the 2 groups of females was similar. Lactating females increased energy intake by 45% (per g^0.75) over that of nonreproducing females. Energy intake and change in body mass of the lactating female each explained about 50% of the variance in infant growth and, therefore, our hypothesis was not supported. Energy intake and change in body mass of the lactating female together explained approximately 76% of the variance in growth of young.