In the critical time around weaning, every little step has to be made as easily as possible for young piglets. Preparing the feed’s protein content in the best possible way, in the right quality and quantity, is one of them.
Around the globe awareness is growing to reduce antibiotic use in pig rearing. For instance, China recently banned colistin and the European Union forbade the use of zinc oxide by 2022 and is pushing for further reduction of antibiotics. In addition, the US Food and Drug Administration (FDA) presented new federal rules in which all 31 antibiotics for growth promotion will completely be withdrawn.
In order to deal with these new challenges, a multidisciplinary approach is necessary. One of the key elements in creating good gut health is making the right nutritional choices. Protein use and digestion will require attention in order to rear piglets in a healthy way with no or few antibiotics.
Gut health is the result of a vulnerable interaction between the host, its microbiota and the environment. A change in that sensitive relationship will lead to gut dysfunctioning and subsequently to health problems. Around weaning, however, changes and stress are inevitable, due to e.g. a new hierarchy, a new environment and a transition from sow milk to a vegetal diet.
As the host is young, microbiota in the intestine are not yet established. Moreover, it is known that enzyme secretion before weaning is low. When piglets are weaned at an early stage (e.g. 21 days), the abovementioned factors will cause an even faster disbalance, a disturbed gut health and eventually post-weaning diarrhoea.
In this context, protein is one of the most important players in keeping the vulnerable balance stable, as undigested (vegetal) protein will rapidly result in bacterial fermentation and pathogen overgrowth.
Avoid undigested protein
Protein digestion can be influenced by many factors.
- For instance, if the stomach is not sufficiently acidified, further protein digestion in the GIT will become more difficult, which may lead to bacterial fermentation. That is why it is important, at feed formulation, to keep in mind the feed’s acid binding capacity. In the stomach, feed with a high acid-binding capacity will have the effect of buffering (increasing) its pH value (also see Table 1). This should be avoided because on one hand, a pH that is too high makes the stomach less bacteriostatic or less bactericidal, on the other, that also inhibits a proper onset of protein digestion. Adding right organic acids through water and/or feed can help the piglet to lower its stomach pH.
- Similarly, in the small intestine the protease enzymes trypsin and chymotrypsin are indispensible, so no undigested protein ends up in the large intestine. As both compounds are only produced in limited amount by piglets, certainly after weaning, any inhibition (e.g. due to badly processed raw materials) will lead to extra undigested proteins.
In general, 2 things can happen with undigested proteins in a piglet’s gut. It will be built in as bacterial protein and be excreted afterwards through the faeces. Alternatively – and this is what happens mostly – undigested proteins will be fermented for energy. The upside of that process is that it leads to branched and short-chain fatty acids, having a positive effect by lowering the pH and supplying energy to the villi.
The downside of protein fermentation, however, has far more impact, as the fermentation also leads to mono-amines, poly-amines, ammonia, hydrogen sulphide, phenols and indoles. As the gut barrier is rapidly affected within 24 hours after weaning, these toxic metabolites of the protein fermentation threaten the intestinal integrity, leading to inflammation.
Growing soybeans on a soy plantation. Photo: Shutterstock
Influence of (soy) protein quality
In short, choosing the right protein source is of great importance in order to avoid protein fermentation. Known products, for instance potato protein, fish meal, rice protein or whey protein concentrate are often used in piglet diets. The most important raw material for protein supplementation in animal husbandry, however, is soybeans. This raw material is globally available and has a good amino acid profile.
There are many ways to offer soy to pigs. Quite expensive soy derivatives are soy protein concentrates, soy isolates, full-fat soybeans, fermented soybeans and enzyme treated soybeans. The most common form to present soy in pig diets, however, is soybean meal.
Whatever soy source one is using, it is generally accepted that it needs processing before usage in animal feed due to the presence of anti-nutritional factors (ANFs). In soybeans, they vary in presence, toxicity as well as heat stability. In relation to protein digestion, soybeans contain specific protease inhibitors – compounds that inhibit proteases to do their job well. A so-called ‘trypsin inhibitor activity’ level is used to indicate the level of trypsin inhibitors present in soy.
|Table 2 - Anti-nutritional factors in soy products.
- Anti-nutritional factors
- Trypsin inhibitor
- Antigenic proteins
- Complex carbohydrates
Adequate heating step
By applying an adequate heating step during the production process, trypsin inhibitors can be reduced to acceptable levels as to not interfere with the protein digestion as stated above. Apart from trypsin inhibitors, soybeans also contain other anti-nutritional factors, like lectins, antigenic proteins or complex carbohydrates, see Table 2. Depending on the soy source, these can be reduced as well. The best known example is a final soy protein concentrate in which antigenic proteins as well as oligosaccharides have been reduced by applying aqueous alcohol extraction. That process leads to a high protein, low ANF-product, to be used in piglet and young animal feed in general.
A side effect of heat treatment of soybean meal, however, is that it can possibly damage the protein structure leading to an irreversible ‘Maillard reaction’ – a chemical reaction between reducing sugars and amino acids. This reaction leads to unavailable lysine for pigs. Measuring reactive lysine can be of use by determining how much of the lysine will be available for protein deposition.
In young piglets, microbiota in the intestine are not yet established. Photo: Ronald Hissink
Standardised Ileal Digestibility
Standardised Ileal Digestibility (SID) values for crude protein and amino acids of soy products are usually published in feed ingredient databases. These digestibility data are used for all categories of pigs, which would suggest that a weaned piglet would have the same digestive capacity as adult pigs.
For most protein sources there is only limited data available on SID for crude protein and amino acid values in piglets. Soybean meal, however, has been investigated in piglets more often. Research confirmed that standard ileal digestibility values for grow-finisher pigs cannot be used as such for piglets, as they are often overestimated.
Moreover, as soybean meal is produced on a large scale around the world, production parameters can vary. Although they are getting more and more standardised, German research in 2012 highlighted that different origins of soybean meal led to different SID values of crude protein and amino acids in early weaned piglets (17 days, on average 5.6 kg).
On average (out of 6 batched per origin) a significant variance in SID level for crude protein between 77 and 80% was noted. These results also confirm the above statement that SID values depend on age. As the SID of crude protein of soybean meal is generally around 85-93% in ingredient databases.
Influence of protein quantity
Offering the right quality of protein is key, and so is offering the right quantity. Several authors have related diets too high in protein levels to dysbiosis and diarrhoea. Too much can possibly lead to a higher flux of undigested protein making the selection for good digestible protein sources even more important. Dominant protein fermenters such as E. coli and Clostridium will get the upper hand and lead to post-weaning diarrhoea.
For that reason, lowering protein content can be a solution to reduce fermentation levels and thus increase piglet health. Recent research by Dr Martin Nyachoti and others, at the University of Manitoba, Canada, showed that low protein concentrations in feed for early weaned piglets reduced toxic microbial metabolites. It is vital, of course, that performance should not be compromised by lowering protein levels too much.
To conclude, both (soy) protein quality as well as quantity are of great importance for piglets and will constitute an important link in the total approach towards pig rearing without antibiotic growth promoters or zinc oxide. A more sustainable business can be achieved by correct processing of soy sources, a good digestibility evaluation and a well-considered formulation.