Physical and biological methods to improve feed nutrition value (review)

An increase in the productivity of domestic animals by 20-30% over the past 50 years has been achieved due to advances in genetics, intensification of metabolic processes and effects on digestion (M. Georges et al., 2019), as well as due to effective preparation of feed for feeding and ensuring greater availability of nutrients for the body (M. Balehegn et al., 2020). Animal feed must have certain qualitative characteristics: it must be nutritious, tasty, clean, easily digested and well absorbed, free of impurities and substances harmful to health and adversely affecting the quality of livestock products (M. Balehegn et al., 2020). Only a small part of the feed fed in its natural form meets these requirements (R.Sh. Fakhrutdinova, 2009). An important criterion is feed conversion, which determines the economic efficiency of the industry, since 70 % of the costs of raising animals are accounted for by feed. The animal's body processes about 20-25 % of the feed energy into products. Approximately 30-35% of energy is spent for physiological needs, and the rest is released in an undigested form with excrement. The task of preparing feed for consumption is to reduce energy losses by changing the physico-chemical properties of the feed, increasing nutritional value, accessibility to the body, namely digestibility and assimilation by animals (R.V. Kartekenova et al., 2013). Various technologies have been developed in the Russian and global production of feedstock to increase the availability of nutritional components. They can be conditionally divided into two groups - physical and biological methods of increasing the nutritional value and availability of feed (A.I., Fitsev 1997). The purpose of this review is to summarize information on the basic (physical and biological) methods of preparing feed for feeding, increasing accessibility, improving their nutritional value and digestibility for farm animals and birds, as well as the principles of their action and application in science and practice. Physical methods involve exposure to temperature, pressure, or other factors, as well as a combination of them. These include both simple methods (for example, soaking with and without germination, frying) and more technologically complex processes - extrusion, expansion (pressure conditioning), micronization, exposure to ultrahigh frequency waves, cavitation (E. Kosmynin, et al., 2006; V.A. Chikulaev, 2020). Biological methods include the use of bacteria, yeast and other microorganisms or their metabolites to break down complex carbohydrates into simpler, easily digestible forms (fermentation) and the production of related substances that can be used by animals (K.S. Krylov et al., 2000; N. Lau et al., 2022). The use of fermentation methods can increase the efficiency of feed use, improve its nutritional value and reduce waste, which leads to increased animal productivity and product quality (L. Yang et al., 2021; L. Yafetto et al., 2023). The presented physical and biological methods of influencing feed components ensure an increase in their digestibility and overall nutritional value due to the degradation of factors that impede effective digestion. Such a strategy seems to be quite profitable in the field of resource-saving technologies in animal husbandry. However, before choosing one or another method, a number of important factors should be taken into account, including energy and labor costs, the degree of destruction of biologically active components and profitability. Keywords: feed, preparation for feeding, nutritional enhancement, extrusion, cavitation, digestibility.