Heat stress hits hard - soybean meal helps pigs stay on track

9 June 2026

7 minute read

By: Sarah Mikesell

North America

Thomas D’Alfonso, PhD, Worldwide Animal Nutrition Focus Area Director, U.S. Soybean Export Council, recently spoke to The Pig Site’s Sarah Mikesell about heat stress challenges that most producers face as temperatures climb during the summer months. 

Every summer, swine producers talk about the weight dip. What's actually happening and why is it so expensive for producers? 

It's particularly expensive for producers because there's an opportunity to get revenue if they can get body weight on the animal and get it to the processing plant at target weight. 

Two things happen during summertime: the heat affects the rate of growth, and it affects feed consumption. Feed consumption can also affect the rate of growth, creating a double whammy. 

The animal is trying to get the nutrients that are needed to reach its genetic potential at the maximum rate of growth. But as the temperature goes up, just like you and I in hot weather, we don't eat as much as we do during the wintertime. So, it's hard to get the nutrients in the animal when their feed consumption decreases. 

You've mentioned dry distillers grains and other byproducts. Why do those ingredients make the summer problem worse? 

There's been a lot of exciting research in the last five years on this exact topic. The industry has been trying to determine what are the best ways to correct for the decrease in consumption and decrease in body weight gain. 

One of the ways to do this is to use a high fiber diet which is low cost. This may include distillers grains, amino acids and some calories and/or supplementing synthetic amino acids to try to balance the diet. 

However, the research has shown that for several reasons the best option is to balance the diet with soybean meal made from U.S. Soy. It's highly digestible in essential amino acids and digestible energy, and it brings other functional compounds that affect the rate of growth and the digestive health of the animal. 

It's so much better to use soybean meal to meet the nutritional needs during the hot summer months as opposed to putting in byproducts such as distillers grains or using synthetic amino acids. The pigs just don't recover their growth during that period. 

Functional compounds seem to be offering additional value that we’re just learning about? 

We think about soybean meal in terms of the nutrient bundle – very high in metabolizable and digestible energy and net energy and very high in essential amino acids and their consistency and digestibility. 

However, what we've learned in the last decade is that there are functional compounds in soy that are bringing health benefits that help to alleviate things like respiratory symptoms, digestive health and inflammation. 

These anti-inflammatory compounds, immune modulators and antioxidant compounds include polyphenols, terpenoids, bioactive peptides and bioactive lipids. There's such a bundle of bioactive, healthy ingredients that are included that we don’t even formulate. We formulate diets based on the least cost of meeting the nutritional requirements.

It's time to really think about the benefit that the ingredients bring beyond lowering the cost of feed and providing those nutrients. They're providing healthy compounds at the same time. 

When nutritionists talk about soybean meal, they usually focus on protein. You're describing something bigger. What else is going on? 

First let me address this protein problem. And I'm going to call it a problem because for the last 30 years, nutritionists have been moving away from crude protein and formulating diets based on digestible amino acids and calories and that's important. 

But we still measure ingredients based on crude protein with methods that are over 100 years old. It's hard to change paradigms; it's hard to change practices that are 100 years old. We don't measure crude protein. We measure nitrogen, and we multiply nitrogen by a factor of 6.25. Both those things are incorrect. Science is well beyond that now. 

We know that protein is really the addition of all the amino acids. But it's costly to measure all the amino acids, so we just measure nitrogen. However, there are other compounds with nitrogen that are not the essential amino acids. 

In fact, I just came back from Indonesia where we were doing a trial. We saw two different soybean meals. One had lower crude protein, but when we added up all the amino acids, it had higher composition. That was using soybean meal derived from U.S. Soy. 

We need to move beyond crude protein. It's really a red herring. It is the essential amino acids and the digestible energy that bring the value in the nutrient bundle along with the functional compounds in soybean meal derived from U.S. Soy. 

When it comes to field trial data, what can producers expect when they adopt a soybean meal-centered summer strategy? 

The economic results are really remarkable. By adopting a strategy of using soybean meal to balance a diet for essential amino acids and calories during the entire production cycle of the animal, particularly for a pig that has a longer production cycle than smaller animals, it means that the animal can get off to a good start. So, it can help get a young pig’s digestive system healthy and properly functioning, but what you also see is during the winter and spring when the animal is susceptible to respiratory challenges, it can have a carryover effect in the summertime. 

The pigs that experienced respiratory challenges earlier in the year are harder hit by heat stress. It could be their immune system, or it could be that their digestive system was affected. Feeding a diet based on soybean meal derived from U.S. Soy, from a young pig throughout the grower and finisher phases, will help the pig perform better during those summer months.

The research, conducted by Iowa State University in commercial operations, shows a $14 per pig extra revenue during the summertime and an extra 6 to 12 lbs. difference in body weight. So, you can improve revenue and reduce costs at the same time by adopting a preference for soybean meal derived from U.S. Soy and formulating diets with it as the base ingredient. 

What's your message to a producer who's skeptical, who thinks this sounds good on paper but wants to see it work in their barn? 

This reminds me of one of our customers from Thailand, from United Feed, who was at a conference, and he said, “The pigs don't lie.” This company produces feed and ingredients for other companies, as well as producing their own pigs, and they're seeing performance. 

They were realizing three Thai Baht per pig, and I was wondering is that a lot of money or not? When you look at the extra bottom line profitability, that is a lot, and the pigs don't lie.

We can formulate a diet, and on paper, we can show that soybean meal derived from U.S. Soy is worth $20 to $25 per metric ton more than soybean meal derived from other origins. We can show how consistency means you need less safety margins. All of this is speaking to reducing feed costs. 

But when we see animal performance differences, that's where the real money is. Even though it's typical to manage animal operations to control costs, when you have opportunities to recover revenue or gain extra revenue, it can come from rate of growth, better feed efficiency and better uniformity. 

All of these affect the revenue that a hog producer can realize by adopting a strategy of having good amounts of soybean meal in a diet. We're talking 25% or so, and the payback comes at the processing plant. Again, “the pigs don't lie,” as our customer said. 

Tom, $14, a pig is a big deal - that's a huge amount of additional revenue you don’t want to miss, right? 

It is a lot – and it comes from lower feed costs and better animal performance during a period of time when performance can be hit extremely hard. That is the summer dip due to heat stress and particularly for animals that experience some respiratory challenges in the winter and springtime. 

You see these big differences, which are very costly differences in performance. The performance can be recovered by balancing the diet with soybean meal derived from U.S. Soy as opposed to adding extra fat to try to get calories or adding extra synthetic amino acids to try to get those nutrients. None of those approaches recover the performance the way that adding high quality soybean meal in the diet does. 

The summer BBQ months spark higher demand and higher prices, potentially creating an opportunity market, right? 

Absolutely, it's when prices tend to be higher because there's a higher demand for those summer cookouts. It's time to focus on revenue as well as cost.