Fermented dairy constitutes a major dietary source and contains lactose as the main carbohydrate and living starter cultures, which can encounter the intestinal microbiota after ingestion. To investigate whether dairy-related nutritional and microbial modulation impacted intestinal microbiota composition and activity, we employed static fecal microbiota fermentations and a dairy model system consisting of lactose and IMPORTANCE: The consumption of fermented food has been linked to positive health outcomes, possibly due to interactions of food components with the intestinal microbiota. This study brings forward new insights into how major constituents of fermented dairy affect intestinal microbial ecology and activity when supplied together or alone. We provide evidence that lactose availability increased the production of butyrate by fecal microbiota through cross-feeding and did not observe a contribution of starter cultures to lactose metabolism, possibly due to a lack of competitiveness. The methodological setup used in this study can be implemented in future investigations to determine the impact of other fermented foods and their major components on intestinal microbiota composition and activity.