By using this method, by grabbing a sample of feces from the pen (or the rectum), digestibility can be calculated in animals kept in confinement or on grazing ruminants. Apparent digestibility (%) = 1 − (% marker in feed / % marker in feces) × (% nutrient feces / % nutrient feed)

Stomach problems can manifest in a variety of ways, and the specific symptoms can depend on the underlying condition. However, some common signs of stomach problems include abdominal pain or discomfort, bloating, gas, nausea, vomiting, diarrhea, and constipation. Other symptoms may include loss of appetite, weight loss, and fatigue. If you experience any persistent or concerning symptoms, it's important to consult with a healthcare provider, who can perform a physical exam and recommend diagnostic tests, such as blood tests, stool tests, imaging studies, or endoscopy, to determine the underlying cause of the symptoms. It's important to seek medical attention promptly if you experience any severe or worsening symptoms or signs of bleeding, such as dark, tarry stools or vomiting blood.

Digestibility is measured by comparing the feed intake (I) to the fecal output (O). For fish, digestibility is calculated by adding an inert indicator (e.g., chromium, yttrium) to the diet and measuring its accumulation in the feces.

• Remaining fraction (NDF) is not ideal and its digestibility must be determined – dNDF = NDFD*NDF • dDM = DMD = dNDS + dNDF USDA-ARS US Dairy Forage Research Center Summative Equations for Calculating Digestibility