Effective rumen degradability and intestinal digestibility of individual amino acids in different concentrates determined in situ

Fifteen different concentrates (xylose treated soyabean meal (Soypass), coconut cake, maize gluten meal, barley, heat treated barley, potato protein (Protamyl), heat treated repeseed meal, rapeseed meal, heat treated rapeseed cake, wheat, heat treated wheat, cottonseed cake, palm kernel cake, maize gluten feed and sunflower meal) were examined for effective degradability in the rumen and intestinal digestibility of individual amino acids using in situ methods. The proportions of amino acid (AA) nitrogen (N) in total N in the intact feeds varied from 0.63 in maize gluten feed to 0.88 in Protamyl. Effective AA degradabilities calculated at a rumen fractional outflow rate of 5%/h varied from 0.51 for Soypass to 0.94 for wheat, and were generally similar to effective protein degradability. After correction for particulate loss from the nylon bags, effective degradabilities of protein were higher compared with effective degradabilities of AA due to higher true water solubilities of crude protein compared with AA. Arginine, cystine and glutamic acid had higher, and valine, isoleucine and threonine had lower, effective degradabilities compared to total AA. Intestinal digestibility of total AA in intact feed varied from 0.84 in cottonseed cake to 0.98 in Protamyl, and generally total AA digestibilities were similar to protein digestibilities. Glutamic acid and arginine had higher and lysine, threonine and glycine lower digestibilities compared with total AA.