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The Gut's Role in Defending Animal Health

Gut health has made its stamp on livestock production as the gateway to animal health. We often think the gut's primary job is to digest valuable nutrients. But an immunologist may argue that a more important job of the gastrointestinal (GI) tract is to prevent the infiltration of unwanted pathogens that can lead to illness and loss of productivity.

Not convinced? Consider these GI tract facts:

  • Around 70% of the immune system resides in the gut.
  • The gut is regularly exposed to trillions of microbes — that's more microbes than there are cells in your body.
  • No matter the species, once the small intestine starts, the GI tract is only one cell thick.

To limit the repercussions of poor gut health, we cannot underestimate the impact of one key factor — stress. As we all know, significant stress on an animal can lead to declining health and performance. However, many everyday environmental, behavioral and physiological stressors — such as vaccinations, pathogen exposure, extreme weather, housing conditions, feed or water restrictions, etc. — can result in small, recurrent intestinal leaks. Also known as Leaky Gut Syndrome, these leaks can possibly lead to systemic problems and irreparable harm to an animal's gut. 

When you put all these factors together, it's not a big leap to realize that gut health is a crucial piece of the puzzle in your herd or flock's overall health.

What is leaky gut syndrome, and how could it lead to systemic health problems?

To understand the impact of gut health, we first need to understand the anatomy of a healthy gut versus a leaky gut. As we discussed, the intestinal barrier has two key roles:

  1. Absorbing nutrients into the bloodstream
  2. Keeping harmful substances from entering the body

To perform these functions well, the intestinal lining needs to be selectively permeable — allowing the good in but keeping the bad out. The intesintal barrier consists of a single layer of epithelial cells, which are knit together by tight junctions when the gut is healthy. When the cells or the tight junctions are damaged, it opens the door for harmful pathogens, bacteria and contaminants to move through the barrier and into the bloodstream. This compromised intestinal barrier is known as Leaky Gut Syndrome (LGS).

Leaky Gut Illustration

"Even in the healthiest of animals, there is some permeability," explained Iowa State University Normal L. Jacobson Endowed Professor in Dairy Nutrition Lance Baumgard, Ph.D. "But, if harmful substances make it through the lining, they will trigger an immune response where cytokines, macrophages and other immune cells attack. When that leak becomes overwhelming and the challenge becomes too much for the immune system, that's when it can lead to systemic issues and even mortality."

A common stress that can contribute to LGS is heat stress. In fact, Baumgard notes that the heat stress costs U.S. agriculture between $4B-$4.5B a year and $2B in the dairy industry alone. Based on the phenotypes we desire (more milk, more eggs, more muscle), the heat stress problem may continue to get worse. 

When an animal is heat stressed, they can experience leaky gut, which causes endotoxemia, as quickly as two hours after the heat stress event. Ultimately, this leads to the immune system being activated.

Why staying on top of gut health is crucial to animal performance and health

Beyond heat stress, everyday stressors can also lead to significant complications. When animals are constantly exposed to stressors — no matter how big or small — the body triggers a defense response. This response can present as common signs of illness, including reduced feed intake.

While reduced feed intake obviously has an effect on productivity (poor weight gain, low milk yield, etc.), the psychological stress also causes the body to release cortisol (among other hormones) that can cause an immune response.

"I don't think it's a coincidence that all these seeming very different stressors — transport stress, hindgut acidosis, tissue trauma, heat stress, overcrowding — can cause significant production losses. Part of its reduced feed intake, the other part is immune activation," said Dr. Baumgard.

Studies have shown that even a 50% feed reduction (caused by stress) negatively impacts the gut, explained Dr. Baumgard. The villi become shortened and fatter — hallmarks of a damaged gut — stripping away the Velcro barrier (tight junctions) and allowing harmful pathogens through the intestinal lining and in to the bloodstream where they can cause harm.

When harmful microbes slip through that lining and into the bloodstream, it triggers and immune activation, which means energy is not going to maintenance, reproduction and growth needs, but rather to the immune response. This results in adverse effects on producer's bottom line.

DIVE DEEPER: Intestinal injury recovery: How it works and the role of feed ingredients

When there isn't an active immune response, livestock and poultry have a hierarchy of nutrient use based on the growth and performance needs for that particular animal. Starting at the foundational functions (maintenance), an animal will utilize energy and nutrients available in the hierarchical order until depleted. When feed intake decreases, fewer nutrients are consumed. In turn, nutrients are used for maintenance functions meaning feed is not readily converted to output development whether that be reproduction, protein accretion, milk yield, egg production or otherwise.


"When hyperinsulinemia occurs (the animal becomes sick or psychologically stressed), the immune system now takes a higher priority. The animal's hierarchy of nutrient use is much more important to withstand an immune response than it is to make milk or to make a chicken or to make a piglet. Reprioritization of nutrient flow, that's all it is. When an animal is sick, making you money is no longer important for them," said Dr. Baumgard.

How to boost gut health and minimize stress

Gut health is synonymous with animal health. To keep your operation healthy and productive, it's important to manage environmental and physiological stressors as well as be attentive to any potential gut health issues they may cause. 

Stress — anything that reduces feed intake or causes physiological stress — can trigger an immune activation, leading to energy and nutrient diversion to the immune response rather than productivity, ultimately impacting your bottom line.

READ MORE: Management changes to minimize livestock stress in both young and older animals

To safeguard your herd or flock's gut health, talk with your veterinarian or nutritionist about incorporating products specifically formulated to boost gut health and keep invasive pathogens at bay.

Hear more from Dr. Baumgard and other gut health experts at

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