Bioavailability of dietary amino acids provided in protein or free form

Bioavailability of dietary amino acids provided in protein or free form

Studying the physiological and metabolic responses of pigs following the ingestion of an unbalanced or unbalanced amino acid profile, in protein or free form.

High quality protein sources is important for both animal and human nutrition. In order to limit the competition between the two, the valorisation of non-conventional protein sources can be a solution for sustainable feed. However, these sources needs to be studied to determine if they meet the nutritional requirements of animals, including a balanced intake of amino acids (AA).
Using an extremely hydrolysed feather protein as a model, the thesis aims to study the metabolic and physiological effects of pig when it ingests a protein source with either a balanced or unbalanced AA profile. The material studied has a high protein content which mostly (≥ 92%) comes in the form of free AA and small peptides. However, its AA profile is severely unbalanced with low levels of essential AA like lysine and high levels of non-essential AA like proline (figure 1).

These specific properties of this material surely has metabolic and physiological consequences when fed to pigs (Yen et al., 2004; Morales et al., 2020). In an initial study, feeding of this feather hydrolysate to pigs induces higher concentrations of plasma AA compared to other conventional protein sources even though the diets were formulated to have the same amount of total AA (Meniga et al., 2017). Furthermore, plasma AA continue to remain elevated in the plasma even after 6 h after the meal (figure 2).


Figure 1. Amino acid profile of the extremely hydrolysed feather


Figure 2. Postprandial plasma concentrations (µM) of total proteinogenic amino acids (TAA) of pigs (n = 3) for 6 h after a meal test with three different experimental diets with the same amount of TAA with  either an extremely hydrolysed feathers, feather meal, or poultry meal

The hypotheses for these unanticipated effects of feeding this material are (1) the consequence of the unbalanced profile of AA or (2) the particular form of dietary protein, composed mainly of free AA and small peptides.

The first objective of the thesis will be to identify the causes of the accumulation of AA in plasma and the metabolic mechanisms of the pig when it ingests the feather hydrolysate by studying the metabolic effects of dietary AA balance on growing pigs or pigs in maintenance (mini-pigs). The implementation of this test on two types of animals will make it possible to compare animals with contrasting protein deposition potential and likely to respond differently to the ingestion of this hydrolysate.

The second objective will be to determine whether the form of the dietary supply of AAs (in the form of proteins, peptides, or free AAs) influences the metabolic and physiological responses studied. In this second experiment, apart from the metabolic effects of the diet, we will study in particular the digestive physiology of pigs (morphology, expression of AA and peptide transporters, etc.).

The project is a CIFRE thesis with the collaboration of INRAE and BCF Life Sciences, who produces the hydrolysed feathers. For the company, this will allow them to acquire knowledge about their product and its use in animal feed.

Francis Amann Eugenio is working on this thesis subject since may 2019 for a period of 3 years. He is supervised by Nathalie Le Floc’h in the team  Adaptation and Jaap van Milgen in the team Alinut.


Francis Amann Eugenio : francisamann.eugenio[at]
Nathalie Le-Floc’h : nathalie.lefloch[at]
Jaap van Milgen : jaap.vanmilgen[at]


  • Morales, A., L. Buenabad, G. Castillo, S. Espinoza, N. Arce, H. Bernal, J. K. Htoo, and M. Cervantes. 2020. Serum concentration of free amino acids in pigs of similar performance fed diets containing protein-bound or protein-bound combined with free amino acids. Anim. Feed Sci. Technol. 267:114552. DOI.
  • Yen, J. T., B. J. Kerr, R. A. Easter, and A. M. Parkhurst. 2004. Difference in rates of net portal absorption between crystalline and protein-bound lysine and threonine in growing pigs fed once daily1. J. Anim. Sci. 82:1079–1090. DOI.

Modification date : 10 February 2023 | Publication date : 18 January 2021 | Redactor : Pegase