Profile of digested feed amino acids from untreated and expander treated feeds estimated using in situ methods in dairy cows

Guar meal, sunflower meal, rapeseed cake, peas, maize, rye, wheat and barley were subjected to expander treatment at different temperatures (95–150 °C), and effect on amino acid availability was assessed using rumen nylon bag and mobile bag in situ methods. Expander treatment of rapeseed cake at 142 °C decreased feed lysine content, probably due to formation of complex compounds. Effective rumen degradability and total tract digestibility of protein, total amino acids, lysine, methionine, threonine, isoleucine, leucine, valine, and phenylalanine were compared to values for the untreated feeds. Effective rumen degradability seemed to decrease due to expander treatment for all cereals, except maize. Effective rumen degradability for sunflower meal and rapeseed cake was unaffected by expander treatment at 115 °C, whereas expander treatment at 142 °C appeared to decreased effective rumen degradability for rapeseed meal. Total amino acid digestibility was not decreased by expander treatment. Both for untreated and heat treated feeds rumen degradability and total tract digestibility of individual amino acids were generally in agreement with results for crude protein. Observed amino acid profiles supplied by digestible rumen undegraded feed amino acids were compared to a theoretical optimal profile obtained from the literature using a χ2-index. A low index is equivalent to a high biological value. Smallest and largest index for the difference between the observed and theoretical optimal amino acid profile were obtained for peas and maize, respectively. Lysine was the first limiting amino acid for cereals, sunflower meal, expander treated (142 °C) rapeseed cake and untreated guar meal, leucine for untreated and expander treated (115 °C) rapeseed cake, and methionine for peas and expander treated guar meal. It was concluded that based on the assumed ideal amino acid profile, expander treatment only changed the first limiting amino acid for rapeseed cake and guar meal, and that although expander treatment decreased the index, and thereby improved the biological value of the intestinally digested feed amino acids, the ranking of feeds based on the index was unaffected by expander treatment.