Passage of feed through the digestive tract is important to quantify supply of nutrients to dairy cows with respect to optimal feeding, environmental pollution and animal health. Knowledge on nutrient passage is limited, among others because of difficulties to estimate nutrient passage with conventional markers.
Stable non-radioactive isotopes were used as an alternative marker. In a series of experiments with dairy cows it was possible to distinguish passage rates of grass silage, maize silage and concentrates, which are typically fed to dairy cows. With the help of stable isotopes it was also possible to distinguish among passage rates of the major feed components fibre, starch and proteins, and quantify passage of minor feed components like plant wax alkanes. It was concluded that stable isotopes can be used as a tool to estimate passage kinetics of various feed types and feed components through the digestive tract of dairy cows.