NorFor update - focus on starch

NorFor model update

A new version of the NorFor model was released on June 4, called FRC 1.76. The new update includes a modified calculation of starch digestibility and a recommendation for individual amino acids. We will come back with more information later on amino acids and focus on starch in this newsletter.

In the previous version of the NorFor model, starch digestibility was considered to be close to 100 %. This has been questioned based on available research data. A meta-analysis with Nordic and international research data was performed at Aarhus University. The results showed that the starch model in NorFor overestimated the digestibility of starch.

In the new starch model, the distribution of digestible starch between the small and large intestine is based on how much of the starch that is degraded in the rumen. The higher degradation of the starch in the rumen, the larger part of the undegraded starch will be digested in the small intestine. The remaining starch, except the indigestible fraction, will then be digested in the large intestine.

This change means that the NorFor feedstuff table will be updated with new values. Soluble starch will be 0 g/kg starch, which means that all starch is characterized as potentially degradable. Feed specific degradation rates for starch are also introduced that will replace the three existing categories of 9, 12 and 40 % per hour (Table 1). The indigestible starch fraction will now be considered to be indigestible in the whole gastrointestinal tract and not only in the small intestine as it used to be. The indigestible starch fraction is calculated, based on data from in vivo trials.
Table 1. Starch characteristics for some feedstuffs, sorted by total tract digestibility

Feedstuffs with low starch content, (approximately less than 50 g/kg DM) will get a fixed degradation rate of 25 % per hour and the indigestible starch will remain unchanged.

Table 2. Consequences for energy values for some starch rich feedstuffs. The difference shows that energy values are reduced, in various degrees.

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Best regards
Patrik Nordgren, CEO