(Bio)Technological processing of poultry and pig feed: Impact on the composition, digestibility, anti-nutritional factors and hygiene

The present review considers the impact of biotechnological fermentation methods as well as mechanical and hydrothermal processes in feed production, on the physical properties, chemical composition, starch and protein digestibility of poultry and pig feed. Reduction of feed particle size and consequently, gizzard underdevelopment in poultry and stomach ulceration in pigs coincide with fine grinding and are also reported as consequences of the common hydrothermal processes e.g. pelleting, expander processing and extrusion. Inclusion of structural feed components containing insoluble fibers with high resistance to grinding may partially counteract these negative impacts in pig and poultry. Hydrothermal processing (HTP) of poultry and pig feed improves the hygiene status of feed, reduces feed wastage, increases feed intake, reduces energy expenditure for ingestion of feed and may reduce allergenic proteins and anti-nutritional factors (ANFs). The impact of HTP on ileal starch digestibility is mainly negative for poultry and positive for pigs. In contrast to the current belief, the direct impact of HTP on chemical and physical properties of proteins in feed and their digestion per se is negligible and if any, it does not necessarily lead to better protein digestion. However, the more intensive hydrothermal processes i.e. expander processing and extrusion can improve protein and AA digestibility of poultry and pig feed through reduction of ANFs. Fermentation processes can effectively reduce ANFs in feed and modify the gut microbiota in pigs and poultry. However, the impact of the fermentation process on nutrient profiles of feed ingredients and their digestibility is rather inconsistent and largely depend on type of fermentation, incubation time, fermentation agent and enzymatic profile of dominant microorganisms in the fermentation process as well as type of feed ingredients and their chemical composition.