Use of soybean products in animal feeding. Part III

Soybean meal (SBM) composition is more uniform and consistent than that of other protein sources used in animal feeding. However, its small viariations become relevant due to the high inclusion rate of this ingredient. Several factors affect SBM composition, the most important being type of bean, conditions during oil extraction (moisture, temperature, time of treatment), country of origin (latitude, soil, rains). This article discusses the relevance of these factors. 

Introduction 

The lower variability in the chemical composition of soybean meal (SBM), compared to other protein sources, encourages its use in animal feeds, despite its price.

Many factors, including processing conditions (Grieshop et al., 2003), storage (Westgate et al., 2000) and origin (Ravindran et al., 2014; García Rebollar et al., 2014 and 2016) affect the nutritional value of SBM.

It is important to consider all those variation factors when formulating commercial feeds, since they influence total feeding costs.

Processing and storage conditions

Prior to the heating process, the beans are chopped and hulled to improve the profitability of the oil extraction process. The dehulled beans undergo different processes, including thermal heating, with the dual purpose of facilitating the extraction of the lipid fraction using solvents (which represents around 18-20% of the whole bean), and reducing the content of thermolabile antinutritional factors (ANF).

Under normal conditions, the resulting SBM contains very low levels of ether extract (around 1.7%) and CP levels between 46 and 50%, depending on the quality of the original bean. On many occasions, part of the hull separated in the beginning of the process is added to the defatted SBM, giving a product with approximately 44% CP. This additional hull is not thermally processed and, due to this, contains certain levels of ANF, such as trypsin inhibitors (TI).

High moisture

If the storage and transportation conditions are not adequate, part of the moisture of the stored beans or SBM migrates and concentrates in certain areas or pockets. The high moisture level in these pockets leads to an increase in temperature, and consequent overheating and product deterioration.

It is necessary to control such circumstances. Storage of beans and SBM in harbor silos, as well as during the transport in poorly maintained ships, are of importance.

The existence of mixed consignments

The characteristics and quality of SBM are variable. This constitutes a problem when it comes to estimating SBM nutritional quality on arrival, since the consignments are mixed, and it is difficult to identify the factories of origin.

Soybean hull inclusion level

Also, soybean hull inclusion levels vary between processing plants, which makes it difficult to determine its final nutritional value. Remember that the most commonly used methods to control SBM protein quality at commercial level are:

• Cresol red
• Urease test
• KOH solubility (KOH)
• Protein Dispersion Index (PDI)

Origin of the soybean 

The world’s leading exporters of SBM are USA, Brazil, and Argentina, followed by China, India, and Paraguay. As reported by several authors (Cromwell et al., 1999; Grieshop and Fahey, 2001; Karr-Lilienlahl et al., 2005; Thakur and Hurburgh, 2007; Frikha et al., 2012), according to the origin of the beans, there are variations in nutritional composition and quality of SBM. This is due to different factors, mainly:

• Processing conditions
• Characteristics of the original beans 
• Type of soil, latitude, weather, daylight hours, environmental humidity, harvesting time.
• Storage conditions

Ravindran et al. (2014), García-Rebollar et al. (2016), and Cámara et al. (2017) evaluated the influence of the origin of the bean on the chemical composition and protein quality of SBM. The authors demonstrated that significant differences exist in the composition and nutritional value of SBM, with possible effects on animal performance.

Proximate and mineral composition

Crude fiber and Neutral Detergent Fiber

In general, research demonstrateed that SBM from USA has less CF and NDF and more sucrose compared to SBM from Brazil, with intermediate values in SBM from Argentina (Table 1).

Crude protein

It is important to note that SBM from Brazil generally contain more CP, but also more fiber, for the same protein level, compared to SBM from USA or Argentina. This is contrary to the general thought that SBM with high fiber content have low CP levels.

Sucrose and oligosaccharides

The differences observed in the contents of sucrose and oligosaccharides (stachyose and raffinose, the latter possibly having antinutritional effects when existing in high levels) can be related to latitude differences between production areas.  Latitude contributes with differences in daylight hours during germination and growth, also affecting the ripeness of the beans at harvest.

To be considered…

The higher sucrose content and lower fiber content of SBM from USA, as well as their better quality and digestibility (estimated by KOH protein solubility), make their AMEn content for poultry higher than that in Argentine SBM and similar to that in Brazilian SBM. However, Brazilian SBM is higher in CP.

Minerals

The mineral content of SBM also varies according to its origin. This is mainly due to differences in soil characteristics, including acidity and use of fertilizers at planting. For this reason, mineral concentration and acidity of Brazilian cultivated soils generally produce beans containing slightly lower contents of phosphorus, calcium, and potassium.  However, beans produced in Brazil have higher iron levels than beans produced in USA.

Cámara et al. (2018) conducted a meta-analysis based on the results of 17 publications, with a total of 1,334 SBM samples.These data largely corroborated the differences in regard to chemical composition and protein quality according to the origin of the beans.

To be considered

In particular, SBM from Brazil had higher levels of CP, CF, NDF, raffinose and iron, but lower levels of sucrose, stachyose and potassium, compared to SBM from Argentina and USA.

The AMEn calculated for poultry based on the prediction equation proposed by WPSA (1989) was higher for SBM from Brazil than for SBM from USA or Argentina:

• AMEn SBM from Brazil: 2,642 kcal/kg DM
• AMEn SBM from USA: 2,615 kcal/kg DM
• AMEn SBM from Argentina: 2,603 kcal/kg DM

However, it should be considered that the prediction equation used for this calculation is exclusively based on the contents of total CP, ether extract, and nitrogen-free extracts. Therefore, this equation considers neither the sucrose content nor the protein digestibility, which are generally favorable for SBM of USA origin. 

Crude protein and amino acids

In general, average CP contents of SBM from Brazil, USA and Argentina are around 48, 47 and 46%, respectively. It should be considered that CP and fiber contents in SBM depend on the genotype and the geographic area in which soybeans were produced (Cromwell et al., 1999; Mateos et al., 2011).  It is also influenced by the quality of the dehulling process and the amount of hulls added after oil extraction. Also, it can depend on the inclusion of urea to increase nitrogen contents, although this practice is very rare in developed countries.

• The studies cited above show that SBM from Brazil have higher CP contents than SBM from USA. At the same time, both CP values are higher than the levels in SBM from Argentina.
• The quality of Brazilian SBM is expressed in Profat, which means that its real CP content is around 46.4%.

In any case, SBM from Brazil contain less Lys, sulphur amino acids and Thr per protein unit compared to SBM from USA or Argentina (Ravindran et al., 2014; García-Rebollar et al., 2016). Therefore, the nutritional value of SBM from Brazil, regarding the protein fraction, is not always higher than that those of SBM from other countries.

Quality control of crude protein

In general, the markers for protein quality (cresol red, urease test, KOH and PDI) favor the use of SBM from USA over SBM from Brazil or Argentina. This may indicate a less aggressive thermal processing in the last two countries.

According to the results obtained by Cámara et al. (2018), the PDI values, solubility in KOH and activity of trypsin inhibition (ATI) were lower for SBM from Brazil and Argentina than those of SBM from USA and India (Table 2).

Conclusion

• The sector must be aware of the economic importance of having an adequate estimate of soybean meal when formulating diets for monogastric species.

• Soybean products are key ingredients in feed formulations and, although its uniformity in relation to the nutritional composition is higher than those of other protein sources, its high inclusion rates requires a better control of this factor.
• It should be considered that SBM can present significant variations in their nutritional value depending on the processing characteristics and the country where the beans were originated.

Therefore, it is advisable, to use, whenever possible, different matrices for SBMs of different origin.

Further reading

Use of soybean products in animal feeding. Part I – Nutritional value

Use of soybean products in animal feeding. Part II – Quality control

This artcle was originally published in nutriNews Spain, under the title “Utilizacion de productos derivados de soja en alimentación animal . Parte III”