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

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Soybean meal (SBM) is the most used source of protein in animal feeding. In this first article of a series of three, the authors review composition and nutrtional value for different species, as well as factors determining their variability. 

 

Introduction

Soybean meal (SBM) is the main source of protein and amino acids (AA) used in animal feed formulations worldwide, particularly for monogastric species. Soybean is a source of high-quality vegetable protein, with a less variable chemical composition than other protein sources. However, due to its high inclusion rates (especially in poultry diets), any lack of uniformity in SBM will have more relevance than a variation in any of the other protein sources added to the formula.

In numerous practical situations, the quality control of soybean meal and derivatives is limited to analyses of moisture, crude fibre, crude protein (CP), and urease activity.

  • Analysing only moisture, crude fibre, crude protein (CP), and urease activity is not enough to accurately determine soybean nutritional value.
  • Other parameters such as sugar content, NDF, AA profile and variables like trypsin inhibitors (TI), Maillard reactions and KOH protein solubility are rarely examined.

All these parameters are relevant. They allow us to properly evaluate the nutritional value of the ingredient. However, these variables are subjected to variations depending on:

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  • seed genotype
  • type of soil and environmental conditions during growth (Westgate et al., 2000)
  • processing characteristics (Grieshop et al., 2003)
  • duration of storage (Serrano et al., 2013)
  • presence of antinutritional factors (Karr-Lilienthal et al., 2004; Frikha et al. 2012)
  • country of origin of the beans (Ravindran et al., 2014; García Rebollar et al., 2014 y 2016).

SBM accounts for the main cost of raw materials in a feed mill.

The objective of present study consists of three parts:

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  1. Identify the main factors affecting the profile and nutritional quality of SBM.
  2. Define and evaluate the different methodologies used to estimate SBM value and determine possible improvements in quality control in the feed industry.
  3. Describe the different types of soybean according to its origin.

 

Nutritional value

What are the existing products on the market?

Different products derived from raw soybeans are available on the market, depending on the type and level of processing (Figure 1).

Soybean products _ Figure 1

Figure 1. Products derived from the soja bean.

Solvent processingsoybean products - Fig 2_ composition

Heat processing

In certain countries, such as Argentina, solvent extraction is not used to remove oil. Instead, a pressure processing in combination with high temperatures is carried out. In this case, the product obtained is the expeller soybean meal with 40-44% CP and 8-11% fat.

This pressure processing is normally performed in small plants, not always with good facilities. Hence, the products are less uniform, and a strict quality control program is needed.

From the processed and degreased soybeans, value-added products can be generated through:

Proximate composition and nutritional value of SBM

The chemical composition of SBM is less variable than that of other protein ingredients commonly used in commercial feeds for monogastric animals. However, given its high inclusion level in animal feeds, a high degree of uniformity is required.

 

Table 1. Proximate composition of soybean meal (47% CP) according to various sources 

proximal composition of soya bean

 

To be considered…

An issue for consideration in practical situations is that most feed mills estimate that the AA proportion (or profile) in SBM is constant. Thus, when the protein level in the matrix is modified, the content of all AA is often modified proportionally. This leads to errors with high impact on production costs.

The availability of AA in soybean is negatively correlated with the presence of ANF, particularly TI and Maillard reactions.

Various studies have demonstrated that the content of essential AA is not proportional to the CP level, and the AA content in soybeans depends not only on its protein content but also on the country of origin of the beans. The SBM received in Europe are often from USA, Brazil/Paraguay or Argentina. In general, soybeans from Brazil/Paraguay contain higher CP levels than those from USA, and these contain higher levels than those from Argentina, provided that hulls are not added to the final product (Table 2).

Table 2. Proximate composition1 (% DM) of soybean meal according to the country of origin of the beans (García Rebollar et al., 2016).

Soybean product_differences accoding to country

The advantage in CP found in the SBM from Brazil/Paraguay is partly lost when the AA profile is examined, since these meals contain lower levels of Lys, Met, Thr and other essential AA per protein unit compared to SBM from Argentina and USA. Therefore, the advantage of a higher protein level is partly lost since the animals do not need protein, but digestible AA.

In the laboratory, CP is calculated by multiplying the N content of SBM by a conversion factor set at 6.25.

icono-alertaThe inclusion of low levels of urea allows for raising the theoretical protein values quite impressively. It should be considered that urea is not toxic for monogastric animals, but its nutritional value for these species is zero.

Energy value of soybean meals

The calculation of SBM energy value is important for the correct estimation of its nutritional value. However, there is no available methodology defined for estimating its value in different soybean products.

In practice, the metabolizable energy (AMEn; poultry) is determined using prediction equations which are based on the possible energy contribution of its immediate principles. The main disadvantage of this method is that it considers neither the possible variation in protein digestibility, nor the sugar content (often higher than 8-9%) (García Rebollar et al., 2016) or the presence of ANF. All these parameters are variable according not only to soybean processing but also to the origin of the beans.

Other values – Moisture, NDF and EE

SBM contains approximately 12% moisture, 7-13% NDF and 1.7% ethereal extract, while ash represents approximately 6%. These values depend fundamentally on the chemical composition of the original bean, its genetics, but also, and perhaps at a higher proportion, on the geographical region where the soybean was produced. The latitude, which is related to the daylight hours during seed growth and maturation, is a probably key factor to understand bean composition.

 

Conclusion

  • Despite its price, soybean meal is a major source of protein for monogastric animals.
  • Due to its high inclusion levels, it is necessary to control the various nutritional parameters, particularly those related to the AA profile, AA digestibility, and sugar and energy contents.
  • The processing plant, the type of soil, and the place of origin of the soybean (latitude) are parameters affecting its nutritional value.

Further reading 

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

Use of soybean products in animal feeding. Part III- Origin

 

 

 

 

 

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

 

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