By Robert Swick, NSM livestock feeding and nutrition consultant

Soybean meal (SBM) is the most common protein source in broiler diets. However, due to processing, soybean genetics and conditions during handling and storage, SBM can widely vary in nutritional composition and protein quality. Robert A. Swick, professor at Poultry Hub Australia, has analyzed 19 samples of SBM originating from the U.S., Argentina and Brazil to evaluate digestible amino acids and metabolizable energy.

Because temperate and tropically grown beans have different ratios of the various amino acids to crude protein, laboratory analysis is necessary when comparing different origins of soybean meal. This information should be continually updated to keep feed formulations accurate and avoid deficiencies or excesses in the field.

The study examined the nutrient profile of 19 samples of SBM from various origins with five from the U.S., 10 from Argentina and four from Brazil. The samples were collected from feed mills in Vietnam, the Philippines, Thailand, Malaysia and Australia and shipped to the Bangkok Animal Research Centre (BARC) in Thailand and University of New England in Australia. Nutrient composition including crude protein (CP), dry matter, crude fiber and ash were analyzed by the standard methods in various laboratories and by near-infrared spectroscopy (NIRS) using calibrations provided by Adisseo. Apparent metabolizable energy (AME) and standardized ileal amino acid digestibility were determined in live broilers at the Bangkok Animal Research Centre in Thailand.

The chemical and NIRS evaluation showed all samples to be of high quality. However, the U.S. meal topped the charts in sucrose, potassium hydroxide (KOH) protein solubility and insoluble non-starch polysaccharides (NSP) or hard fiber. The Brazilian SBM was highest in crude protein, about one percent higher than both the U.S. and Argentina meal samples.

So, what does this mean?

Soybeans contain sucrose that remains in SBM after oil extraction. Sucrose is highly digestible and contributes to the metabolizable energy in the meal. Soybeans grown in cool climates tend to have more sucrose than those growing under warmer tropical climates

Swick says the high levels of sucrose in U.S. meal could be related to ideal bean storage conditions, contributing to higher digestibility by the broilers. Digestibility is important because it determines nutrients available for meat production.

Insoluble NSP correlates to hard fiber and could be expected to have a positive impact on gizzard function. The lower soluble NSP of U.S. meal may reflect the fact that more of the sugars are in the form of sucrose and less are present as oligosaccharides.

Improved gizzard function from the higher levels of hard insoluble fiber increases nutrient digestibility. Soluble fiber on the other hand is often associated with digestive disturbance such as sticky droppings and excess gas production in the hindgut, meaning low levels are a positive attribute.

The analysis also showed total lysine to be highest in U.S and Argentina meal, while cystine, arginine and glutamic acid were highest in Brazil SBM. No differences in valine or methionine were found between the meals. These differences confirm previous studies showing higher lysine in meal produced from temperate beans and high non-essential amino acids such as glutamic acid in meals produced from tropical beans. Thus, Swick recommends that amino acids should not be adjusted solely based on crude protein in the formulation matrix.

The apparent metabolizable energy (AME) content was highest in U.S. SBM and sucrose content was positively correlated to AME. The coefficient for standard ileal digestible lysine was highest for U.S. meal compared to other meals. Methionine, cystine, threonine and valine were also found to be more digestible in U.S. meal as compared to Brazil meal.

The nutrient values and amino acid digestibility values were used to formulate broiler starter, grower and finisher diets using prevailing ingredient prices in Asia. With U.S. SBM at USD 630/mt, Argentine meal would need to be USD 4.60 less expensive in starter and grower diets and 7.80 less expensive in the finisher diet before it could be feasibly used. The Brazil meal would need to be $7.70 less expensive in starter and grower and $14.70 less expensive than U.S. meal in finisher feed.

The results show an economic advantage for U.S. meal being in the range of USD $4.60 to $14.70 over Argentina and Brazilian SBM. The results also show that crude protein values should not be used to adjust amino acids in SBM and sucrose is positively related to caloric content in SBM for poultry.

The soybean industry currently uses the proximate analysis method developed in Weende, Germany in 1865 to value the quality of SBM. Swick suggests that soybean meal should be valued on its content of metabolizable energy and digestible amino acids rather than crude fiber and crude protein. These research results suggest that infrared spectroscopy, when properly calibrated, may give a more robust estimate of nutrients important for meat production.

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