Is there a best time for a mouse to be pregnant? Carrie Straight 05.25.01 In many animals the age of the mother affects how she takes care of her young and the development of those young. Some researchers chose mice (Mus musculus) to see if differences in the growth of her babies (called pups) differed as mother mouse’s aged changed. Mice are a perfect organism to use as a study species. Mice produce many young each year and are fairly easy to watch. So, the researchers studied pregnant mice at three different ages (35 days, 3 months, and 9 months). They counted each of the mother's pups and measured the pups’ weights at different ages and then compared these measurements. They found out that the 3 month-old females had the most young (about 12), the 35 day-olds had the second highest number of pups (about 10) and the 9 month-olds had the fewest number of pups (about 7). The weights of the male pups followed the same pattern, with the “young adult”, 3 month old, mothers having the heaviest male pups. This might mean a lot to a mouse because heavier mice probably have a better chance at living in the wild. Wang, Ming-Hseng, and Fredrick S. vomSaal. 2000. Maternal age and traits in offspring. Nature 407: 469-470. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.