In Vivo and in Vitro Studies with Growing Pigs on Standardised Ileal Amino Acid Digestibilities in Grain Legumes

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Since there is a general ban on meat and bone meal and its by-products in diets for livestock in the EU, it is crucial to focus on alternative protein feed ingredients to be used in pig nutrition. Beside soybean meal as a commonly used plant protein supplement, grain legumes may also be used as alternative protein sources in diets for pigs. Current protein evaluation system for feed ingredients for pigs are based on the concept of standardised ileal digestibilities (SID) of crude protein (CP) and amino acids (AA), but there is a scarcity of information on SID of CP and AA in grain legumes grown in Central Europe. Therefore, the objective of the thesis was to determine the chemical composition and the SID of CP and AA in seed-grade cultivars of faba beans (Vicia faba), peas (Pisum sativum) and lupins (Lupinus spp.) in growing pigs using the difference method. Furthermore, to obtain SID of CP and AA, the basal ileal endogenous CP and AA losses in growing pigs were estimated by means of regression analysis from apparent ileal digestible and total dietary contents of CP and AA. A further aim of the thesis was directed to the validation of an in vitro procedure for estimates of SID of CP and AA in the same grain legumes by means of a two-step enzymatic method with subsequent pepsin and pancreatin incubations. The in vitro predicted SID values were compared with their corresponding in vivo SID values. The chemical composition and SID values of CP and AA measured in faba bean, pea and lupin cultivars generally were in good agreement with tabulated values. The average SID of CP and most AA in lupin cultivars (CP, 87%) were higher than in pea (CP, 79%) or faba bean cultivars (CP, 76%) Comparably low SID values in some faba bean cultivars can be partly explained by their contents of condensed tannins. In contrast to SID values in faba bean cultivars, there were only small variations in SID values between individual cultivars of peas or lupins. Results of the in vitro experiment revealed that predicted SID of CP and AA do not provide direct estimates of SID values in grain legumes, because the in vitro predicted SID values were generally higher than in vivo SID values. The use of multiple linear regression analysis with grain legume species as a covariate resulted in strong linear relationships. Further investigations are warranted to study if these principles apply to other feed ingredients as well. Moreover, the use of in vitro predicted SID values in practical diet formulations for pigs needs to be further validated.