WPX: Finding the soybean meal sweet spot for maximum pig performance
New research shows both too little and too much soybean meal can reduce growth, carcass weight and overall profitability
By: Dr. R. Dean Boyd, with Animal Nutrition Research, recently spoke to The Pig Site’s Sarah Mikesell at the 2026 World Pork Expo in Des Moines, Iowa, USA, about soybean meal inclusion rates in swine diets.
When it comes to including soybean meal to maximize growth and efficiency, can you put too much or too little into swine diets?
Indeed, you can put too much into diets. We’ve provided our specifications that show the amount of soybean meal to be fed for each phase of diet if gain is at a premium. If you feed 15% or more than we recommend in our curve, then it's possible that you may have some reduction in gain. It's also possible that too much soybean meal would result in some reduction in carcass yield, so we've been very careful not to overdo it.
How does this affect amino acid levels and energy levels?
As one uses more soybean meal, which is what we recommend for maximum growth, feed conversion and lean percentage, it does not alter the diet energy markedly. It gently increases diet energy realized in commercial systems. One gets a little better feed conversion because of it.
Increased use of SBM also has an effect on synthetic amino acid use. In general, amino acids decline with the exception of methionine.
What about carcass leanness and carcass yield? Does too much or too little soybean meal have a negative effect?
We have produced a new fact sheet to address these questions. We have learned that if one feeds an extraordinary amount of soybean meal, it's going to decrease the yield of the carcass. The whole-body weight will not typically be altered, but the carcass yield will be altered.
If you feed to the levels suggested for maximum gain and feed conversion, you also will get the maximum lean percentage. If you feed below that, if gain is not a priority, then feed conversion will hurt a little bit, and carcass lean will decline as well.
How should swine nutritionists and producers strike the best balance for soybean meal inclusion rates?
This is a matter of pure economics. I come from the integrated swine production system where diet type was defined by maximum profit or minimum loss. So, I did not devise our nutrition plan around least-cost formulation. Our team-based diets on maximum profit – that's what I was hired to do.
When growth is at a premium, as it often is for summer harvest pigs, those diets should be initiated in February. Those diets will cost you $5 to $7 more per ton than what the least-cost formula provides. Fasted gain cannot be delivered without this investment, but these diets improve feed conversion efficiency and carcass lean percent.
Recently, United Soybean board has leveled the financial field by funding an economic prediction tool. The Feed4Profit decision tool has been developed by Dr. David Rosero's team at Iowa State University. Drs. Bart Borg and Aaron Gaines also played a key role in the tool’s development.
The tool can be used to help you determine when to maximize gain for summer harvest pigs, or not. In about one out of every three summers, you don't want to maximize gain because you'll lose money anyway. This decision tool can help you immensely and for considerations beyond soybean meal.
In addition, there are other times when feeding the level of soy we recommend is a profitable venture and this tool can help you decide that as well. The most important goal is to feed to eliminate summer carcass dip. The rest of the year you feed according to what the Feed4Profit tool recommends.
What are the key takeaways?
As a nutritionist, I would not have done my job properly if I computed least-cost formulations without first deciding what type of diet was needed to maximize profit.
Our guidelines highlight that there are times when you want maximum gain, and for those times, you need to feed a minimum of soybean meal. In the process, you will also get improved feed conversion by 3 to 4 points and lean content will also decrease.
When you're maximizing gain and growth rate, there are two things that are vital. One, you need to feed the right level of soybean meal that we've estimated under commercial conditions. Two, although we have a cheaper protein source in DDGS, we cannot use them to the extent we've been using them. If you feed over 8% DDGS, there's no amount of soybean meal that's going to help you. DDGS are a feed-intake limiting ingredient and we need to understand its impact on performance outcomes, especially in finishing pigs under summer heat stress.
There’s a new soy fact sheet available titled Can Dietary Soybean Meal Levels be Too Low or Too High? Tell me about it.
Readers may be aware that we produced a book containing 11 papers that document the new research and information that we're providing for the first time to the public arena. Since then, we anticipated that there would be questions coming forward that need to be addressed in a timely manner.
We just produced the first fact sheet. It addresses the question of whether there is a level of soybean meal you can feed that is too high. The answer is yes. If it's too high, then you can slow down gain a little bit. If it's more than 15% higher than our recommendation, you may have a decline in carcass yield.
Where can people go to find more information?
Readers can go to the swine home page on can.ussoy.org. They can acquire the fact sheet here, place an order for the Feedstuffs article series book by requesting a copy on the contact form or download one of the papers published in the book
This is not a matter of just trying to benefit from soybean usage. Our diets have become terribly imbalanced. I helped bring forward half the amino acids. When DDGS came to market, we imbalanced the diets, and the pigs didn't perform as well. This effort is to bring us back in balance with the various ingredients. This will help our pigs perform well, so the industry can maximize profit.
Brought to you by U.S. Soy. Fully funded by the Soy Checkoff.
Sarah Mikesell
Sarah Mikesell grew up on a five-generation family farming operation in Ohio, USA, where her family still farms. She feels extraordinarily lucky to get to do what she loves - write about livestock and crop agriculture. You can find her on LinkedIn.
24 July 2026
2
minute read
