Summary: Changes in fecal energy loss can result in differences in net energy balance and feed efficiency, and may result from, e.g., alterations in bile acid production, secretion or re-uptake, and changes in activities of enzymes involved in macronutrient digestion or uptake (e.g., pancreatic lipase). This assay will be coupled to food intake determinations and will involve fecal collection and feces weight measures for 48h, which can be coordinated with the meal pattern studies (catalog item D4003) or indirect calorimetry (catalog item D4007). Specific components (crude protein, dry matter, ash, and fat), will be measured by proximate analysis in fecal samples to in order to assess fat or protein absorption.