In vitro techniques for the assessment of the nutritive value of feed grains for pigs: a review

The philosophy inherent in developing in vitro digestibility assays for die tary energy and protein is reviewed and an historical account is given of t he development of such assays for the pig. General principles to be conside red in the development of in vitro digestibility assays are discussed, as a re limitations of the in vitro approach. The importance of choosing the mos t appropriate in vivo measures of digestibility for the evaluation of in vi tro assays is stressed. For protein sources that do not contain anti-nutrit ional factors or plant fibre, 'true' ileal digestibility should be the in v ivo baseline, while plant proteins should be tested against 'real' ileal di gestibility. There is a dearth of adequately conducted validation studies f or in vitro digestibility assays. It appears that the 3-step (pepsin, pancr eatin, Viscozyme) closed in vitro system to allow prediction of organic mat ter and gross energy digestibility in the pig has particular promise for pr actical feed evaluation. Similarly based protein digestibility assays may r equire further development before they can be applied with confidence.