Indigestibility: An overlooked factor in piglet diets?

Digestibility is considered the most important quality parameter of a nutrient, and many articles on piglet feeding focus on this aspect of the ingredients, but in this article nutritionists Dr Carsten Pedersen and Lars Sangill Andersen of Hamlet Protein discuss what happens when you try to measure indigestibility and thus quantify what’s in the feed that piglets can’t digest

When evaluating feed ingredients, digestibility of nutrients as a measure of quality and potential in feed formulation is typically used. These values are published in various nutrition guides and are often the target of research projects to verify published data or shed light on new hypotheses.

However, recently we’ve become more interested in nutrient “indigestibility”, the undigested protein in the raw materials. This is relevant to what happens further along in the digestive tract, after easily digested nutrients have been absorbed, to the fraction that’s not digested.

Indigestible protein may cause potential gut health problems, which makes it interesting in how it affects health, as well as from a growth perspective. And it’s also worth noting there’s an energy cost involved in excreting nitrogen from de-aminated amino acids.

Developing digestibility
Using 48% crude protein soya meal, the standardised ileal digestibility (SID) was calculated for three different weight groups: piglets (<20kg), growing pigs (20-50kg) and finishing pigs (>50kg). The SID was 9% higher in the pigs heavier than 20kg than in those less than 20kg. These results showed that young animals needed highly digestible ingredients, and there should be a difference in ingredients used for weaned piglets versus growing/finishing pigs (Ball and Moehn, 2016).

We calculated the consequences of not taking digestibilities into account and have been able to show the benefit of formulating according to actual protein digestibility. In Table 1, a simple weaner diet is used as an example. Control diet A is based on wheat, whey, fishmeal and soya meal (48% CP), while in diet B the soya meal and fish meal is replaced with a highly digestible soy protein from Hamlet Protein. Both diets were balanced with amino acids, to a SID Lys of 1.40% and using the ideal protein concept.


The feed formulation in diet A has more crude protein, but is lower in digestible protein, which means in total that diet A contains 3.02% undigested protein. Diet B only contains 2.11% undigested protein, which is 30% less than diet A.

This undigested protein can be fermented in the gut by proteolytic bacteria, and stimulating these harmful bacteria brings a potential risk of an imbalance in the microflora with subsequent diarrhoea. Furthermore, the ammonia formed in the gut is absorbed and contributes to the nitrogen load, which has to be removed by the liver and excreted from the kidneys via urine; all of which costs energy and takes up capacity in the liver from other metabolic outputs, which will repress growth and possibly health.

The conclusion is that the indigestible content of raw materials doesn’t contribute to support the growth and health of young animals. It does, however, add to their health risks and maintenance costs.

Get Our E-Newsletter - Pig World's best stories in your in-box twice a week
Will be used in accordance with our Privacy Policy

About The Author