The Canadian Institute of Health Research (CIHR) and other scientific organizations have raised concern about the variability and lack of reproducibility of animal experimental results between laboratories. This concern includes studies investigating the microbiota, their metabolites and their impact on the host. Factors such as environment, stress, and sex have been identified as possible contributors, whereas composition of the regular diet, specifically quality of macronutrients, has received less attention. The prebiotic properties of dietary FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols) are known to have a profound influence on the microbiota based on human studies, but the FODMAP content of standard animal diets has not been measured. The aim of this study was to analyze the FODMAP content of common rodent diets. Standard rodent chows used at rodent suppliers and research institutions were selected for analysis of FODMAP content, and three mill dates were collected for each chow. Using established protocols at Monash University, following sugar extraction, samples were analyzed in triplicate for excess fructose, lactose, sorbitol, mannitol, galacto-oligosaccharide (GOS: raffinose and stachyose), and total fructan content using high-performance liquid chromatography and enzymatic assays. The FODMAP content was then compared to both a custom-made low and high FODMAP rodent chow containing fructose, sorbitol, fructan and GOS at levels designed to mimic human consumption. Data was analyzed using unpaired t-tests. The custom-made low and high FODMAP diets contained 0.51 and 4.10g/100g total FODMAP, respectively. The total FODMAP content of the six standard chows was variable (Fig 1); the lowest was the Research Diets AIN93G Growing Rodent chow derived from cornstarch, the highest was the LabDiet 5001 Rodent chow derived from corn and soybean meal (0.40 vs 4.62 total FODMAP). When comparing the three lowest to the three highest chows, a significant difference in FODMAP content was observed (mean±SD: 0.89±0.57 vs 4.26±0.34; p=0.0009, unpaired t-test). The total oligosaccharide (GOS + fructan) component, the subgroup known to have the greatest influence on the microbiome, varied from 0.40–2.75. This study points to a significant variability in FODMAP content between commonly used standard rodent chows, which will likely impact gut microbiota composition, and gut physiology. Thus, the use of different standard rodent chows between laboratories might explain, at least partially, the lack of reproducible results in rodent experiments. Figure 1. Total FODMAP content of standard rodent chows compared to the custom-made low and high FODMAP chows CIHRCanadian Nutrition Society