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Low-tannin US sorghum a viable alternative in swine diets

Given the market volatility concerning cereals, U.S. sorghum emerges a viable option for swine diets worldwide.

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Selective Focus On Maturing Seed Head Of Sorghum Bicolor
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Interest in US sorghum has increased around the world as other cereals become more expensive and less readily available

Compared with other major cereals, sorghum is less known worldwide. Yet, when one brings up the folklore image of a witch on a broom, then everyone knows sorghum. That broom was more likely than not made from a specific variety of sorghum (vulgare) that is still cultivated throughout the world for this specific purpose.

Nevertheless, our discussion here is focused on grain sorghum (bicolor), the only variety among 25 existing that is used for this purpose. And, although a native of Africa, with archeological evidence going back at least eight millennia, grain sorghum today is a major crop in the U.S., where it has managed to distinguish itself from other grain sorghum commercial hybrids worldwide.

US sorghum is free of the tannins problem

U.S. sorghum is the only low-tannin sorghum that has resulted as an agreement among the interested parties including the seed genetics – an effort that began in the late 90s. Since then, seed genetics companies in the U.S. have managed to remove tannins from grain sorghum through traditional genetic methods. Here, it merits mentioning that U.S. sorghum is always non-GMO – in other words, there is no GMO sorghum cultivated in the U.S. – a feature not shared with other common cereals.

Going back to tannins, we must mention that being tannin-free does not mean zero tannin concentration. Something like that would be naturally impossible as no natural system is 100% efficient (hence the need for GMO in some cases). As with any toxic substance, it is the concentration that matters the most. Thus, U.S. sorghum contains such low levels of tannins that they cause no adverse effects when consumed at levels that correspond to sorghum being the only cereal in a pig diet.

Results from monitoring U.S. sorghum tannin levels indicate concentrations below the established threshold. The 2021-22 U.S. sorghum quality report, published by the U.S. Grains Council, indicated that “tannin levels in all 97 samples were less than 4.0 mg CE/g, implying an absence of tannins, the same as in 2020-21 and 2019-20.” For reference, values near or below 4.0 mg/g catechin equivalents (CE) indicate absence of condensed tannins. In contrast, tannin-rich sorghum hybrids have values greater than 8.0 mg/g CE.

In order to permanently close the tannins chapter when it comes to U.S. sorghum, we should mention that tannins are not an undesirable component per se. In fact, several tannins have a strong antioxidant activity that we should not ignore in modern animal nutrition. However, condensed tannins are rather undesirable (and again, not in all species) because they bind and precipitate proteins, reducing amino acid digestibility and absorption.

On the other hand, hydrolyzable tannins with antioxidant properties still exist in the colored seed coat of sorghum, but these are not the ones in question. Condensed tannins that have been removed from U.S. sorghum existed in the layer just beneath the seed coat layer. Although U.S. sorghum remains “bicolor” (brownish orange) these pigments are in fact a boost of antioxidant activity and not a hindrance to protein digestibility.

Research on feeding US sorghum to swine

Research on feeding U.S. sorghum to swine goes back several decades and, in fact, Kansas State University – where I received my master’s degree – has done considerable work on the subject. In the mid-90s when sorghum contained some appreciable levels of condensed tannins, research indicated that it had a value of 90-95% compared with corn.

More recent research with modern low-tannin varieties has indicated that this figure has increased to 95-105% versus corn, which in practical terms means U.S. sorghum today is at least as good as corn – the latter always taken as the “gold” standard of cereals for such comparisons. Of course, all such trials used 100% sorghum versus 100% corn, meaning that modern U.S. sorghum can be the only cereal in a pig diet. A plethora of research trials can be easily retrieved from the sorghum checkoff website at www.sorghumcheckoff.com.

Practical experiences from feeding US sorghum

I had the opportunity of working as a field nutritionist in the U.S., where we had to formulate feeds mainly with corn and soybean meal. However, due to my educational background from Kansas, a major sorghum-producing state, I was also given the task of formulating pig feeds with sorghum. This was done either in combination with corn or even without it, with sorghum being the only cereal. And, that was at a time when U.S. sorghum was not of the modern low-tannin varieties.

I can attest that once all nutrients in sorghum versus those in corn were rebalanced, the two cereals could replace one another. Later on, during my work in Europe, I employed that same experience again to help pig farmers incorporate imported sorghum into their pig formulas. There, I had the opportunity to use sorghum versus other cereals, such as wheat and barley, which are used as frequently as corn. Again, with proper balancing of the feeds (never a 1:1 replacement), sorghum stood alone without the need to include a second cereal, meaning there was no problem from condensed tannins.

Testing US sorghum at farm level

This last section of our discussion concerns pig farmers outside the U.S., especially during the present geopolitical circumstances where cereals are more expensive and less readily available compared with just a year ago. Indeed, based on discussions within my network, there appears to exist tremendous interest in testing U.S. sorghum, not only in the EU but also in Latin America and Asia.

With the support of U.S. Sorghum Checkoff Program, we run three commercial demonstration pig trials in the EU, with results expected in the second quarter of 2023. From these trials, we have already learned a great deal about handling U.S. sorghum from the export port until it is ground at the destination farm. I must insist on the following if you plan on testing U.S. sorghum:

  1. Buy from a reputable source, preferably as close to the U.S. sorghum farming industry as possible, to ensure fresh product.
  2. Buy U.S. Grade #1 or at most #2 for all trials and have it tested for moisture and mycotoxins (standard export procedures).
  3. Make sure the fumigant used is permitted under your country regulations.
  4. Use suitable shipping containers prepared to house such material in bulk for a long trip abroad.
  5. Ensure U.S. sorghum is correctly labeled according to local customs regulations.
  6. Use ship carriers that know how to handle grains in containers to protect them from sea moisture (they will close and open ventilation ports and even cover exposed containers).
  7. Make sure the grain is as dry as possible at export point and test again upon receiving.
  8. Ensure the receiving farm has the ability to handle container shipments. This is important and can be a real bottleneck in the whole procedure.
  9. Grind sorghum using a 3-4 mm sieve; sorghum is smaller than corn, but it is harder and more pasty, so very fine grinding is not optimal, especially now that energy prices are so high.
  10. Do not change protein sources or additives during the same trial; only change the cereal source.
  11. Rebalance test diets according to your specific goals; I start with growing-finishing pigs.
  12. Make a list of parameters you want to observe (for example, growth, carcass lean yield, fat color, etc.)

Given the market volatility concerning cereals, U.S. sorghum emerges a viable option for swine diets worldwide. Modern U.S. hybrids do not contain enough condensed tannins to cause toxicity problems in pigs. Sorghum can be used alone or in combination with other cereals. Testing any new raw material at farm level requires attention to product-specific idiosyncrasies. Always conduct such demonstration trials with the best-quality U.S. sorghum.

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