Antinutritional factors
Unconventional feed resources including many agriculture by-products are rich in  antinutrients and toxic constituents, and tannins being the most widely occurring antinutrient. There is a need to generate data for true protein digestibility of agriculture byproducts in mono-gastrics and to understand how this digestibility is affected by antinutrients present in these byproducts. This can be reliably achieved using the 15- N dilution technique by infusing 15-N labelled leucine. This technique permits quantification of undigested feed protein and endogenous protein at the ileum.

Anti-nutritional substances are defined as ‘those generated in natural feedstuffs by the normal metabolism of the species from which the material originates and by different mechanisms exerting effects contrary to optimum nutrition’. Alternatively, anti- nutritional factors in livestock feeds may also be defined as substances which by themselves, or through their metabolic products arising in the system, interfere with feed utilization and affect health and production of animals.

Classification
The deleterious substances can be divided into five groups based on their basic structural units and chemistry: substances protein by nature (e.g. protease inhibitor, haemagglutinins, etc.); substances glycosides by nature (e.g. goitrogens, cyanogens etc.); polyphenolic compounds (e.g. gossypol, tannin etc.); chelating agents (nitrate and oxalates); other anti-nutritional factors have been kept in miscellaneous category.