Protein quality of feedstuffs for pig feed is not known with accuracy. In order to ensure correct meeting of pig requirements, feed producers apply large safety margins in protein supply, which lead to an increase in nitrogen excretion in the environment.
Imported soybean meal is also preferred to European protein sources (peas, faba beans) because the protein value of the latter is not clearly defined. Moreover, pig waste excesses require changes in the management of production, which affect European producer's competitiveness and have a negative socioeconomic impact.
The project objective'is to improve scientific knowledge of protein utilization in pigs, to better understand amino acid digestibility, the effect of dietary factors on endogenous ileal AA losses, the metabolic expense for endogenous losses and the interaction occurring between proteins and dietary factors in the small intestine.
The new knowledge is urgently needed to help resolve a crisis arising from lack of internationally accepted system of pig feed formulation, based on AA digestible content of the feedstuffs. Currently, diets are formulated on basis of apparent ileal AA digestibilities. However, diets with an equal apparently digestible content AA but differing in protein source can give very different N retentions. Such discrepancies dissuade feed producers that pigls requirements can be covered with accuracy and incite them to increase the protein content in the diets, in order to avoid any deficiency in essential AA. This leads to an increase in N excretion in the environment.
Recently, tables were proposed with standardized ileal digestibilities, i.e. an apparent value corrected for ileal endogenous AA losses. With this system, only basal endogenous losses, naturally occurring from the animal, are considered. However, total endogenous losses may greatly exceed this basal value, due to the occurrence of feed specific losses. These additional endogenous N losses must be compensated more than proportionally with a really digestible AA supply since recent data suggested that the metabolic expense for the synthesis of endogenous digestive proteins is high: 1.8 g dietary ideal protein would be required for 1 g endogenous protein lost at the terminal ileum.
Novel stable isotope methodologies will allow, for the first time, distinguishing between the ileal endogenous and dietary flow for each AA whereas, formerly, it was possible only for total N. It will then be possible to calculate the real ileal digestibility of each dietary AA and the endogenous AA flow specific of each feedstuff.
Thus, the series of experiments proposed here will provide the scientific framework for the development of a new system based on really digestible AA content of feedstuffs and a correction for the ileal endo encus protein losses specific of the diet.
The project will be divided in 3 parts:
1. Determination of the real ileal AA digestibility and of the ileal endogenous AA losses specific of the main European plant protein sources for pigs: whea barley, peas, faba beans and rapeseed meal, in comparison with soybean meal. Total endogenous AA losses and real digestibility will be derived from combi results of labelled animal (15N-leucine blood infusion) and labelled diet (15N-labelled feedstuffs) experiments. Feedstuff-specific losses will be calculated as the difference between total and basal losses measured with Ndiets.
2. Assessment of AA metabolic expenses associated with the excretion of endogenous N. Approach of their variation according to 4 different dietary f which cause an increase of the endogenous losses: wheat bran fibres, pea pro peas fibres, lectins.
3. Control of the additivity of the really digestible AA content of the feedstuffs and of the ileal endogenous AA losses and validation of the new system through growing experiments.
Significant improvements of the isotope dilution technique should be obtained in the use of 15N-labelled diets as well as in the practice of 15N-leucine blood influsions. The programme also includes the development of a new analytical methodology involving GC-combustion-IRMS assay of 15N-labelled AA enriched at low level, allowing extension of the measurements to individual AA rather than total nitrogen. The determination of the AA metabolic expense for endogenous protein synthesis and the study of the additive or interactive relationship of really digestible AA and endogenous losses are also original contributions.
The information will provide the basis of the new AA availability system required for the development of low-proten feeds, reducing N excretion without affecting pig performance.
Funding SchemeCSC - Cost-sharing contracts