A recent study evaluated the effects of varying levels of trypsin inhibitor activity in broiler feed ranging from 1.4 to 6.4 TIA units/mg, using soybean meal and extruded soybeans of different TIA concentrations. 

The National Institute of Agricultural Research in Argentina found that feed containing 2.4 TIA units/mg, did not affect broiler performance. However, levels above 3.4 units/mg were found to negatively impact broiler growth performance in a significant way. 

TIA and broiler weight  

Broilers fed TIA levels of 3.4 and 4.4 units/mg had intermediate final weights about 3 percent less than birds fed very low levels of TIA. Birds fed 5.4 and 6.4 units/mg had the lowest weight at 49 days of age (about 6-9 percent less than birds fed low-TIA diets). 

Feed utilization efficiency was negatively affected only at the highest levels of TIA concentrations (about 6 percent worse than low-TIA treatments). It was estimated that broilers fed the highest level of TIA would require at least three extra days to reach the same final weight as birds fed the lowest levels of TIA.

The effects on body weight and feed efficiency parameters were in accordance with pancreas size, which was found to be enlarged in broilers fed diets rich in TIA levels. TIA refers to the inhibition of natural proteolytic enzymes, which causes the organism to secrete higher quantities of such enzymes to make up for their reduced efficacy.

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If TIA intake levels are high, this compensation mechanism is not adequate and growth performance is lost. Based on these results, it can be possible to use TIA concentrations in soybean products as a nutrient specification parameter during feed formulation. If TIA levels are known, then the concentration of soybean products can be adjusted to prevent performance losses. 

Soybeans in broiler feed  

Alternatively, if soybean product levels in broiler feed are inflexible (such as in the case of simple maize-soybean meal diets), then soybean processing can be fine-tuned at the production site to minimize TIA levels. The extra cost to reduce TIA levels in soybean meal (or extruded soybean products) should always be less than the current profit loss.

Anti-nutritional factors are present in soybeans, but their presence is largely ignored as they are assumed to be destroyed by heat treatment during the oil solvent extraction process (soybean meal) or extrusion (full-fat soybeans or extruded-expeller soybean meal). Unfortunately, some residual anti-nutritional factors cannot be avoided as total elimination would require the protein to be overheated and thus denatured, which would reduce the nutritive value of protein.

Currently, quality in terms of anti-nutritional factors is best determined by the level of TIA, with residual levels ranging from as low as 2-3 units/mg or as high as 20-30 units/mg. Unfortunately, such information is rarely available, especially in the case of standard soybean meal, and although young non-ruminant animals find it difficult to handle soybean anti-nutritional factors, this aspect has never been quantified with sufficient detail, at least in the case of broilers.

Source: Iglesias and Azcona (2012) Albéitar 159:34-36.