Metabolic availability of lysine in feedstuffs determined using oral isotope delivery

Using the indicator amino acid oxidation technique in a standard curve assay, the availability of lysine in feedstuffs for pigs was determined using oral isotope delivery. In 8 barrows, 20 kg initial weight, indicator oxidation responded linearly to increasing levels of free lysine at 50, 60, 70 and 80% of requirements. The availability of lysine in peas was reduced from 75.8% to 68.3% after heating. Adding back the lysine lost during heating restored the availability to 76.5%. Using this method, the availability of lysine in soybean meal (87.5%) was similar to reported true ileal digestibility, while that in canola meal (71.4%) and cottonseed meal (75.1%) was lower and greater, respectively. The results for peas demonstrate that this method responds sensitively to small changes in lysine availability. Therefore, using oral isotope delivery with this method is suitable to determine the bioavailability of amino acids in feedstuffs for pigs.