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10 frequently asked questions about soybeans

Soybeans remain the most important protein source for farmed monogastric animals like poultry, pigs and rabbits, and a substantial protein source for ruminants like non-grazing dairy cattle, sheep and goats.

soy-plant-germinating-from-soy-seeds
UrosPoteko | iStockPhoto.com

Soybeans remain the most important protein source for farmed monogastric animals like poultry, pigs and rabbits, and a substantial protein source for ruminants like non-grazing dairy cattle, sheep and goats. Nevertheless, it's not only newcomers to the business of animal feeding that require education, but also old hands who often confuse the different terms used for the same ingredient by nutrition professionals. The scope of this article is to answer the most frequent soybean questions encountered in my work as a consulting nutritionist in the past 20 years. 

1. What is the difference between soybean meal and cake? 

Today, these two terms are used interchangeably to referred to the soybean byproduct resulting after the extraction of oil by a solvent. The residual product is called soybean meal and contains about 1 to 2 percent remaining oil. Older methods were less efficient, and the resulting product had a higher percentage of oil, hence the term cake. In other protein sources, such terminology remains valid. For example, cottonseed meal and cottonseed cake are two different products.

2. What is 44 percent soybean meal?  

The 44, 46, 48 or even 50 percent figure represents the crude protein concentration in soybean meal. The difference reflects the amount of hulls added back to the soybean meal during processing; so, 44 percent soybean meal contains more hulls (and less protein) than 48 percent soybean meal, which, in turn, contains less fiber than 44 percent soybean meal. It is important to realize this because 44 percent soybean meal has not only less protein, but also less energy due to the diluting factor of the soybean hulls. This can be desirable, for example, in gestating sows or ruminants, but also a problem, as in the case of diets for young or highly productive animals.

3. Is soybean meal the same as extruded beans? 

No. Soybean meal, the commercial commodity, is extremely low in residual oil. Whole extruded soybeans retain their full oil content (about 18 percent), and the nutrient composition and nutritive value are different. They both retain the same anti-nutritional factors. Both are valuable products used for different applications. On a protein/energy level, extruded full-fat soybeans are more expensive than soybean meal and as such they are reserved for special feeds. Improperly treated can be worse than soybean meal, whereas proper thermal treatment can make extruded beans a far superior product. 

4. What is expeller soybean meal? 

First of all, expeller soybean meal is a very confusing product for most of us. It is better understood as a product placed in the middle between soybean meal and extruded full-fat soybeans. Whole beans are heated and then expelled (kind of extruded) to remove as much oil as possible. The resulting product contains a variable level of residual oil that can be as high as 4 to 8 percent depending on the efficiency of the expeller. This can be a product of variable quality, but once quality is assured, it can be used like the full-fat soybeans (taking into account the reduced oil/energy concentration). 

5. Why are calcium levels in soybean meal always high? 

Soybean meal producers add at manufacturing about 0.5 percent limestone (which can be of variable calcium content, unless it is pure calcium carbonate) to increase the flowability of the meal. This causes an increase of about 0.1 to 0.2 percentage units in calcium concentration in soybean meal. It is not much, but it adds up as limestone is used in many other products (such as premixes, medicines, additives). 

6. What is the best quality index for soybeans? 

Urease activity is one very common index (laboratory test) of quality, but it is not adequate in all cases. Other indexes exist, but they all come with shortcomings. In general, each laboratory will suggest the best tests to perform, and values should be considered in comparison with historical records from the same source. For animals of young age, an extra index is required, trypsin inhibitor activity (TIA), that is performed by certain, but not all, laboratories. 

7. Soy protein concentrate or isolate? 

Soy protein contains about 60 to 65 percent protein, whereas isolate is about 80 percent. The isolate form is invariably more expensive than the concentrate per unit of protein. This is because the isolate is produced for human supplements, whereas the concentrate has a use only in animal feeding. Subpar quantities of isolate are often available at attractive prices, but the use of isolate should be made by keeping in mind that it is not just a more concentrated source of protein. The two products are made with a different method. The one used for the concentrate reduces the protein allergenicity for young animals, whereas this does not happen in isolate production. 

8. Are there country differences among soybean meal exporters? 

Yes, there are numerous and easily accessible reports discussing the various sources. However, depending on these resources alone, one may exclude the individuality that exists among different soybean crushing plants within a certain country. When buying commodities with unknown parentage, one should take into account country of origin, but it is best to judge based on previous experiences by crushing plant (if possible). 

9. Can raw soybean meal be fed to animals? 

Raw soybean meal can be fed to animals, but only to certain species, and within certain limits. Perhaps in the future, with the development of proper enzymes or probiotics, it may be possible to feed whole raw soybeans to all animals, but we are not there yet. Thus, with a few notable exceptions — that are best left unmentioned and discussed only with a very qualified nutritionist — soybeans should be fed only after some form of thermal treatment (like most, but not all, legumes). 

10. Can soybean meal be 100 percent replaced?

Soybean meal can definitely be 100 percent replaced, but care should be taken to ensure anti-nutritional factors are not increased in the diet and protein digestibility is not reduced. For this, it is important to understand the anti-nutritional factors in the new protein source and how they impact animal performance and especially feed intake (some have bitter taste). Also, it is best to formulate on a digestible-amino acid basis, instead of a total-amino acid basis, and formulate down to the fifth and sixth essential amino acids. 

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