Evaluating the Role of Dietary Protease in Broiler Diets with Varying Trypsin Inhibitor Levels

Soybean meal (SBM) remains a cornerstone protein source in broiler nutrition, yet variability in trypsin inhibitor (TI) content can influence protein utilization and digestive physiology. Research has shown that elevated TI levels are associated with reduced efficiency of protein digestion and amino acid availability in poultry, as well as changes in pancreatic activity and size as birds respond to enzyme inhibition (Herzberg and Rogler, 1982; Clarke and Wiseman, 2007). These physiological responses can translate into less efficient growth performance when TI content increases in SBM-based diets (Clarke and Wiseman, 2005). As a result, managing TI variability continues to be an important consideration for nutritionists balancing ingredient quality, diet formulation strategies, and overall production efficiency (Liener, 1994).

To address the challenge, NOVUS conducted a research trial to evaluate the impact of dietary protease in combination with phytase supplemented at a high rate on broiler performance. 

The study’s 1,224 male broilers ate diets with different TI content: low at 1.47 mg/g and high at 2.57 mg/g feed, and with different protease inclusion: either zero or 250 g per metric ton (g/MT), equivalent to 0.55 lb/US ton. All diets were supplemented with phytase at 1,500 FTU/kg.

Birds were fed corn–SBM–based pelleted diets over 56 days. Feed was pelleted at 80 °C/176 °F. Performance parameters such as body weight gain (BWG), feed conversion ratio (FCR), and carcass characteristics were analyzed.

Across the full 56 day period, higher TI levels were associated with lower BWG and higher FCR, alongside a 20% increase in pancreas weight. These responses highlight the physiological cost of elevated TI content, even in diets formulated with a high level of phytase.

When protease was included at 250 g/MT, birds consuming high TI diets experienced a recovery in growth efficiency. BWG increased by 140 g/0.31 lb, and FCR shifted favorably by four points compared with high TI diets without protease. 

Carcass data further illustrated the role of protease. Supplementation with protease was associated with a 10 g/0.022 lb increase in tenderloin weight and a 1% increase in carcass yield. TI level alone did not influence carcass yield or weight, suggesting that growth responses were primarily driven by digestive interactions rather than carcass deposition limits.

These results demonstrate that phytase inclusion at 1,500 FTU/kg supports nutrient availability, but it does not fully compensate for higher TI levels in SBM. Inclusion of a dietary protease, specifically CIBENZA® DP100 Enzyme Feed Additive, supported growth efficiency and carcass outcomes when TI content increased, even with high levels of phytase.

For nutritionists managing variable SBM quality, this research reinforces the importance of aligning enzyme strategies with ingredient risk profiles. Protease supplementation can play a targeted role in sustaining performance and digestive efficiency when TI levels are elevated, rather than being viewed as redundant alongside phytase at a high inclusion level. 

References

Clarke, E., et J. Wiseman. 2005. Effects of extrusion conditions on trypsin inhibitor activity of soybean meal and the performance of broiler chickens. Br. Poult. Sci. 46:735–742. doi:10.1080/00071660500391574
Clarke, E., et J. Wiseman. 2007. Effects of variability in trypsin inhibitor content of soybean meal on broiler performance and pancreatic hypertrophy. Anim. Feed Sci. Technol. 134:344–352. doi:10.1016/j.anifeedsci.2006.08.007
Herzberg, G. R., et J. C. Rogler. 1982. Effects of dietary trypsin inhibitors on pancreatic function and protein digestion in chicks. J. Nutr. 112:153–160. doi:10.1093/jn/112.1.153
Liener, I. E. 1994. Implications of antinutritional components in soybean foods. Crit. Rev. Food Sci. Nutr. 34:31–67. doi:10.1080/10408399409527649