Voluntary lactose ingestion in gerbils, rats, mice, and golden hamsters.

Over a period of 20 days, adult male gerbils, rats, mice, and hamsters were allowed to choose between tap water and a sugar solution (either sucrose, glucose, or lactose) presented in increasing concentrations (maximum concentration = 24% weight/volume). Rats, mice, and hamsters preferred both glucose and sucrose solutions to water across a wide range of concentrations; gerbils preferred sucrose solutions at concentrations of 8% and above, but preferences for glucose solutions were not significant. Gerbils, mice, and rats did not prefer lactose solutions to water at any concentration, and actually preferred water at higher lactose concentrations; in contrast, hamsters preferred lactose solutions to water at concentrations of 4% and above, and never preferred water to lactose solutions. As solution concentrations increased, all species consumed increasing amounts of glucose and sucrose (i.e., solute). The lactose intake of gerbils, rats, and mice tended to remain quite low even as solution concentration increased; in contrast, the lactose intake of hamsters was substantially greater than that of other species and increased to a maximum of 1.95 g/100 g body weight/day at the 24% concentration. These results indicate that gerbils and mice, like rats, have a low preference for lactose and consume very little of this disaccharide, and confirm that golden hamsters are exceptional in demonstrating both a preference for lactose solutions and an apparent tolerance to the effects of ingestion of substantial amounts of lactose.