Milk Composition of Two Precocial, Arid-Dwelling Rodents, Kerodon rupestris and Acomys cahirinus

We collected milk samples from two rodents, Kerodon rupestris and Acomys cahirinus, that live in arid habitats and produce precocial young, in order to determine milk composition throughout the lactation period. Milk from species producing precocial young has been predicted to be low in energy and protein content, while milk from arid-dwelling species has been predicted to be high in total solids. Milk samples were analyzed for total fat, protein, and sugar content. Milk from Acomys was much higher in energy content than Kerodon milk, exhibiting higher concentrations of total solids (41% vs. 20%), fat (21% vs. 6.9%), and protein (12% vs. 66%); however, sugar concentration was lower in Acomys milk (2. 9% vs. 5.3%). Milk composition varied throughout the lactation period in both species, with protein levels increasing and fat levels decreasing in Kerodon and sugar levels decreasing and total solids and fat levels increasing in Acomys. The milk of Kerodon females exhibited a threefold variation in fat content, while milk from Acomys females showed a twofold variation in protein content. The results of this study lend some support to the idea that mammals inhabiting arid environments conserve water by producing milk with a high proportion of solids. Furthermore, these results do not support the hypothesis that milk from rodents with precocial young is low in energy content but instead indicate that precocial species produce milk that is high in total solids and fat.