Part III: In-feed Mitigation

By Rob Patterson, CBS Bio Platforms

In Part I of this series, the challenges associated with using alternative soybean ingredients such as cooked, whole and full fat soybeans as well as expelled and extruded soybean meal from a Trypsin Inhibitor (TI) exposure standpoint were reviewed. Here it was concluded that various global disruptors have contributed to a substantial increase in the price of conventional soybean meal which has led to an increased use of the aforementioned ingredients. This increased usage has in turn, inadvertently exposed poultry and livestock to excessive levels of dietary TI which could be impeding performance and profitability.

Part II looked at ways and means to monitor levels of TI both in feed as well as within individual ingredients, be it soy based or otherwise. The key takeaway being that there are various methods that are commercially available that can be used to initiate a TI monitoring program. Each method has its own pros and cons related to precision and accuracy on one axis and cost and convenience on the other. However, no matter which method(s) is/are selected for a monitoring program, implementing said program is what is important. The final part of this series will delve into strategies for mitigating in-feed TI.

Once a monitoring program has been established and verified to be capturing accurate data the final step in managing TI is the implementation of one or more mitigation strategies. In practice, such a program should include integrating ingredient and final feed TI levels into existing formulation programs. As a rule of thumb, conventional soybean meal has a TI range of 1.6 - 5.0 mg/g while other ingredients such as extruded soybeans or full-fat soybeans will be 2-3X higher. Once these values are established one mitigation/management strategy is to include monitoring results into feed formulation software as a maximum value that would trigger ingredient rejection prior to being made available into a final feed. However, the amount of TI that is acceptable in final feeds is a nebulous number and is dependent on the species being fed as well as the stage of production. For example, nursery piglets have a lower TI threshold than fattening pigs and the same pattern is generally true for poultry species. Recent work has shown that dietary TI levels of 3 mg/g has the potential to significantly reduce amino acid digestibility in 21 day old broiler chickens, but that levels as low as 1.6 mg/g could begin to negatively impact certain amino acid digestibility values (Figure 1).

Of course, managing poultry and livestock TI exposure via feed formulation is easier said than done. Thus, the use of feed processing technology could be explored as an alternative means of managing TI exposure. If such a program involves the use of heat and pressure treatment of the final ration via a pellet mill, expander or extruder the upfront and recurring costs associated with equipment installation, maintenance and management could be prohibitive. However, if this equipment is already in place for the management of feed-borne pathogens such as Salmonella, then the case could be made to expand said program and include final feed TI as a control point within a feed mill’s quality program. In such a scenario, final feeds would be routinely monitored for TI levels pre- and post-processing to ensure that the amount is not in excess of an established level. Taking the approach of treating TI as a feed contaminant is admittedly unorthodox, however, given the risk to performance and profitability that dietary TI exposure poses, such a re-think to established practices may be justified.

Another strategy to manage TI in commercial feed production is the use of exogenous enzyme technology. Although the typical use case for dietary enzymes is for improving nutrient digestion and feed efficiency, there is a growing body of evidence that suggests that using certain proteases can enzymatically denature feed TIs. However, in order to understand the mechanism of action underpinning this, one first needs to appreciate the physical structure of soybean trypsin inhibitors.

Soybean TIs belong to the Kunitz group of inhibitors and are typically 20,000 daltons in weight (relatively small) and are composed of 170-200 individual amino acids. For the most part, TI have two subunits that are linked by 1 or 2 intra-chain disulfide bridges formed between two cysteines which provide both structure and function to the overall molecule. It follows that targeting these disulfide bridges enzymatically will lead to a loss of structural integrity thereby denaturing the TI. Enzymatic denaturation tends to be less effective than denaturation by heat/pressure when evaluated in vitro. This is likely because the duration of heat/pressure is longer and the application more homogenous which results in a more effective inactivation step during feed manufacturing. However, the cost to implement an enzyme treatment step tends to be lower than the costs associated with new equipment installation as described above. Furthermore, depending on the enzyme technology being used, the use case of improving protein nutrition by reducing the inclusion of soybean meal within a ration can also be incorporated into a feed formulation program, which if done effectively, can result in substantial savings on a per tonne of feed basis.

Managing in-feed levels of TI through external mitigation is not an impossible task as there are both basic and complex strategies currently available for most commercial feed manufacturers. Nonetheless, the mitigation strategies that have been laid out above should in no way be viewed as ‘one or the other’. In fact, combining various strategies together should be considered if at all possible as no single approach is 100% effective at managing the risk to performance and profitability that livestock and poultry are exposed to when overexposed to dietary TI.