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Soybean meal delivers more energy than previously thought

New research suggests that soybean meal provides 105-125% of the net energy of corn, when used as a feed ingredient for growing pigs.

By Lisa M. Balbes, Ph.D., SmithBucklin

Quantifying the effects of soybean meal (SBM) as a feed ingredient on swine growth performance is crucial to maximize farmer profit.  As processing methods have improved over time, SBM has become a  high quality and consistent source of highly digestible amino acids (AAs), but SBM also provides energy. The NRC (2012)  lists the digestible (DE) and metabolizable energy (ME) content of SBM at 105 and 97%, respectively, that of corn. But when expressed on a net energy (NE) basis, SBM’s NE value is only 78% that of corn – but recent field data and studies have called that value into question.  

For a long time, swine nutritionists have been trying to determine the best way to quantify the energy values of various feed ingredients. Traditionally, DE or ME values have been used. However recently, there has been greater implementation of the NE system in swine diets, which more closely correlates with growth performance.  However, direct or indirect calorimetry to measure DE and ME is very labor-intensive and requires expensive, specialized equipment. Therefore, some have suggested a more practical approach , feeding pigs increasing amounts of SBM and using the differences in caloric efficiency to estimate the energy content of SBM relative to the known energy of corn. 2

Two experiments reported in a recent paper4  indicate that SBM actually delivers between 105% and 125% of corn energy, which is significantly higher than the traditional published value in the NRC.  This new value was determined by feeding swine diets with increasing amounts of SBM but balanced for essential amino acids, and observing changes in feed efficiency and caloric efficiency (CE, the amount of calories needed to produce a pound of weight gain). If there is no change in feed-to-gain ratio (F/G) or caloric efficiency (CE) as SBM levels increase, then the designated energy value used for SBM is accurate. However, if the F/G and CE change, the energy value of SBM is incorrect. Specifically, it F/G and CE improve, then there is likely more energy in SBM than initially estimated.  

Henrique Cemin and colleagues at the Department of Animal Sciences and Industry at Kansas State University in collaboration with nutritionists at JBS USA, Greely CO, set out to measure the net energy value of today’s SBM. In the first experiment, 2,233 pigs were fed diets containing 21, 27, 33, or 39% SBM for 21 days, with 23 replicates of each treatment.  The amount of corn in the diet was kept the same, but the inclusion rate of feed-grade amino acids was varied. In the second experiment, a total of 3,796 pigs were used, and they were fed diets with 17.5, 22, 26.5, 31, 35.5, or 40% SBM.  In each case, pigs were weighed and feed disappearance was measured weekly, then used to calculate average daily gain (ADG), average daily feed intake (ADFI), feed-to-gain ratio (F/G), and caloric efficiency (CE).  

The results were intriguing.  In experiment 1, there was a tendency (linear, P = 0.092) for a decrease in ADFI as SBM increased. There was also a tendency (P = 0.090) for a quadratic response for ADG, with a decrease in ADG observed with 39% SBM inclusion. Both F/G and CE improved with increasing SBM content, indicating that its NRC (2012) energy value was underestimated.  Using a value for corn energy of 2,672 kcal/kg NE, the NE of SBM was calculated to be 2,816 kcal/kg, or 105% of corn energy.  

Experiment 2 showed a linear decrease in ADFI as SBM increased, and tendencies for ADG to decrease, but again, like experiment 1, F/G and CE improved.  Using the data from the second experiment, the energy value of SBM was calculated to be 125% of corn energy, or 3,332 kcal/kg NE.  Taken together, these results suggest that increasing the amount of SBM in swine feed improves both F/G and CE.  It also indicates that the energy value of SBM is considerably higher than the current literature standard value, and probably in the range of 105 – 125% of corn, or between 2,816 and 3,332 kcal/kg.  

There is the possibility that the beneficial results of SBM were derived not simply from energy content, but partially from a specific component of the SBM, such as isoflavones, which have been shown to have anti-inflammatory, anti-oxidant and anti-viral properties.  Furthermore, changes in carcass composition were not evaluated in these studies. Regardless of the reason for the increased energy estimate, nutritionists should take this new data into consideration when formulating swine diets.

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