Effect of Corncob Bedding on Feed Conversion Efficiency in a High-Fat Diet-Induced Prediabetic Model in C57Bl/6J Mice

Laboratory facilities use many varieties of contact bedding, including wood chips, paper products, and corncob, each with its own advantages and disadvantages. Corncob bedding, for example, is often used because of its high absorbency, ability to minimize detectable ammonia, and low cost. However, observations that mice eat the corncob lead to concerns that its use can interfere with dietary studies. We evaluated the effect of corncob bedding on feed conversion (change in body weight relative to the apparent number of kcal consumed over 7 d) in mice. Four groups of mice (6 to 12 per group) were housed in an individually ventilated caging system: (1) low-fat diet housed on recycled paper bedding, (2) low-fat diet housed on corncob bedding, (3) high-fat diet housed on recycled paper bedding, and (4) high-fat diet housed on corncob bedding. After 4 wk of the high-fat diet, feed conversion and percentage body weight change both were lower in corncob-bedded mice compared with paper-bedded mice. Low-fat–fed mice on corncob bedding versus paper bedding did not show statistically significant differences in feed conversion or change in percentage body weight. Average apparent daily feed consumption did not differ among the 4 groups. In conclusion, these data suggest that corncob bedding reduces the efficiency of feed conversion in mice fed a high-fat diet and that other bedding choices should be favored in these models.Abbreviations: CC, corncob bedding; HF, high-fat diet; LF, low-fat diet; P, paper beddingThe Guide to the Care and Use of Laboratory Animals (the Guide) is used as a reference for the standard of care for many laboratory animals. Under rodent housing, the Guide suggests the use of contact bedding on solid-bottom caging for all rodents for both enrichment of environment and to absorb urine and minimize ammonia buildup.² Many beddings that have been tested for absorbency, comfort, cost, biodegradability, toxicity, and effects on research are available for rodent housing.^9,11 Corncob bedding is a common choice for rodent bedding because of its biodegradability, ability to decrease the amount of detectable ammonia,⁷ high absorbency per unit volume,¹ and cost.An active area of animal research involves modeling the weight gain that is seen in the average human diet in Western societies and that induces insulin resistance and prediabetes. Unintentional effects of housing conditions, including the potential effects of corncob bedding on metabolic parameters, need to be avoided in these models. In addition to uncontrolled dietary intake, corncob bedding has been associated with decreased time spent in slow-wave sleep, presumably because of decreased comfort⁴ in rats. These findings prompt the concern that corncob bedding might also alter activity status, a parameter affects intended weight gain.Here, we conducted a retrospective analysis of weight gain, apparent feed consumption, and feed efficiency of mice housed on corncob bedding compared with recycled paper bedding and fed either low-fat or high-fat diet. This study resulted from a noticeable reduction in expected weight gain in an established high-fat–fed mouse model of obesity and prediabetes after animals were moved from one building within a facility that routinely uses recycled paper bedding to another building that uses corncob bedding. This decrease in weight gain continued for weeks past the expected acclimation to transportation and the new facility. We hypothesized that this suppression in weight gain was associated with the use of corncob bedding.