Protein and Amino Acid Digestibility in Cereals and Protein Meals by Pigs

At present it is difficult to meet either of these requirements with accuracy because of the difficulties involved in measuring aminoacid availability. Various methods have been used and each method is probably satifactory for determining relative availability of particular amino acids between feeds. Difficulties in choosing correct values appear when several different methods are used, and in many cases it would seem that the use of total amino acid content would be better than the figures for individual amino acids now in common use. The most commonly known published values for amino acid availability for a range of feeds are probably those presented by Feedstuffs (1976), but these appear unsuitable for practical use. Not only are the figures for the different feeds determined by different methods in different laboratories but also only one availability figure is used for all amino acids in each feed. The use of one figure, although simple, is incorrect and often misleading as the availability of different amino acids does vary. Methionine is considerably and consistently more digestible than threonine (Purser 1976); Holmes et nZ (1974) reported values of 93 and 74 percent digestibility for methionine and threonine respectively in rapeseed meal. Moreover, the differences between amino acids are not always consistent; Soares and Kifer (1971) determined amino acid digestibility by ileal analysis in chicks and found lysine in cottonseed meal only 48% digestible compared to an average of 65% for all other amino acids, whereas in soyabean meal, lysine digestibility of 82% was slightly greater than the mean, of 79%.