Prediction of the total tract digestibility of energy in feedstuffs and pig diets by in vitro analyses

An in vitro method consisting of a three-step enzymatic incubation for the prediction of total tract energy digestibility is described. The effects of all relevant parameters in the incubation conditions on the in vitro digestibility were investigated carefully in order to obtain a method with a general validity for all common feedstuffs used in pig diets. A close linear relationship between the in vitro enzyme digestibility of organic matter (EDOM) and in vivo total tract digestibility of energy (dE) was demonstrated for 90 samples of 31 different feedstuffs: dE, % = − 14.0(±2.1) + 1.106(±0.026) × EDOM, % (n = 90, r2 = 0.94, RSD = 3.4, CV = 4.4). Five samples of meat and bone meal and raw potato starch were overestimated or underestimated, respectively, by the in vitro method. These two feedstuffs were therefore not included in the equation. On the other hand, the equation was also valid for experimental pig diets which were formulated with a considerable variation in feedstuff composition and also including diets with these two feedstuffs. A close relationship between determined dE and predicted dE for these feed mixtures by the use of the above equation was found (n = 34, r2 = 0.87, RSD = 2.3, CV = 2.9). Thus, the described in vitro approach for energy evaluation appears to have a significant potential for practical purposes.