Da Shi and Dr. James House, Department of Food and Human Nutritional Sciences, Faculty of Agricultural and Food Sciences, University of Manitoba
Soybeans contain significant amounts of protein (40–50%), lipids (20–30%) and carbohydrates (26–30%), and they represent an important source of nutrients for livestock and humans alike. Soybean production occurs globally but is dominated by Brazil and the United States. Canada currently represents just 2% of global production.
The soy sector in Canada has evolved over the past two decades. In 2000, soybean production in Canada was estimated to be 2.7 million metric tonnes, with the bulk of production (85%) occurring in Ontario (with no production in western Canada). Fast forward 20 years and Canadian soybean production now exceeds 6.1 million metric tonnes, with Manitoba accounting for 19% of total production. However, production in 2020 was down from the historic highs of 2017 (2.25 million metric tonnes).
This changing soybean landscape has led to the availability of new varieties suited to Manitoba production. Unfortunately, these varieties have resulted in lower crude protein values. Several factors influence protein and amino acids profiles, including variety, environment and the interaction between the two.
A comprehensive review authored by researchers from major government and academic research settings in the United States (Assefa et al. 2019) detailed the genetic, environmental and management factors contributing to soybean composition. The authors benchmarked several factors influencing soybean protein composition as production moved north, including planting date and maturity group (genetics). Under the same growing conditions, different varieties of soybeans contain different protein and amino acids concentrations. Conditions like temperature, water availability and sunlight affect protein content.
Understanding this interplay between genetics, environment and management is highly beneficial to the soy sector in Manitoba. One current focus is on identifying soybean varieties that will produce high protein levels in Manitoba.
Right now, the lower protein levels we are seeing in northern soybean crops present a barrier to further development of the Manitoba soybean sector. This is because protein content plays an important role in determining both the price and value of the crop. In 2017, soybeans that presented 33% protein (on a 13% moisture basis) received a $6-per-tonne discount from one major buyer. Even more serious, soybeans with 32.4% protein or lower may have received discounts approaching $9-per-tonne.
The traditional focus on protein content of soybeans relates to the importance of the meal as a livestock feed ingredient. However, feed formulation strategies have evolved away from a primary focus on crude protein content to a focus on digestible amino acid content. Amino acids are the building blocks of proteins. And animals, including humans, require a dietary source of available essential amino acids.
Essential amino acids (EAA) cannot be synthesized by the body at a rate satisfactory with its demand and must be provided in the diet. Diets with high crude protein content but limiting or deficient in one or more EAA cannot support growth and production targets and lead to excess nitrogen release in the manure.
A more accurate reflection of soybean quality is the concentration of primary limiting EAA in livestock feeds, namely lysine, cysteine, threonine, methionine and tryptophan. The sum of these amino acids is the critical amino acid value (CAAV) used by the soy sector in the northern U.S. These are generally the limiting amino acids in swine and poultry feeds, formulated from cereal grains (corn, wheat) and soybean meal. A higher CAA content would improve the feeding value of Manitoba soybeans and allow feed formulators more flexibility in formulating rations.
In order to identify soybean varieties capable of yielding high contents of the CAA, research in our laboratory has been focused on the development of high capacity, accurate and non-destructive methods for the rapid assessment of protein and amino acid content in Manitoba soybeans to support varietal selection and breeding efforts. In collaboration with the Manitoba Pulse & Soybean Growers, we have secured samples from the regional variety trials conducted in 2018 (2700 samples) and 2019 (2000 samples). We are using a process called Near Infrared Reflectance (NIR) spectroscopy to determine the amino acid composition and the CAA of soybeans varieties available in Manitoba.
Figure 1 depicts the variability in crude protein content of soybeans from 2018 and 2019. The average (minimum; maximum) values of crude protein (%) for the 2018 and 2019 cropping years were 35.79 (25.37; 46.75) and 35.55 (28.06; 47.07), respectively. These data show that there is considerable variability in protein content, and understanding the factors influencing this variability will be important in guiding soybean development and selection for Manitoba conditions.
While low protein values (<33%) are present within these cropping years, the data in Figure 2 highlights the importance of considering the CAAV in addition to protein content to understand the true feeding values of the soybean meal for livestock feeding in particular. There is a negative relationship between the CAAV and the total protein content for Manitoba-grown soybeans, similar to observations that have been made in the northern U.S. As such, the true feeding value of Manitoba-grown soybeans may be underestimated if the focus is kept solely on the crude protein content.
This assessment of soybean varieties best suited to meet market demands is important for the soybean sector to continue to advance in Manitoba. Our continuing research will lead to the development of new tools to predict the quality of the protein contained in locally-sourced soybeans. The development of rapid assessment methods, including the use of NIR, will provide the sector with tools needed to determine the true nutritional value, with respect to protein nutrition, for soybeans grown in northern regions, including Manitoba.
Assefa, Y., Purcell, L. C., Salmeron, M., Naeve, S., Casteel, S. N., Kovács, P., … & Lindsey, L. E. (2019). Assessing variation in us soybean seed composition (protein and oil). Frontiers in plant science, 10, 298.