Impaired gut integrity and its consequences

Gut integrity is the unimpaired condition of the gut and maintenance of its essential functions to absorb nutrients and act as a barrier to pathogens. The inside of the gastrointestinal tract is considered to be a part of the external environment because it is a continuous tube connected to the exterior and contains ingested foreign material. The single cell layer of the intestine must be able to effectively absorb nutrients and defend against harmful agents in order to preserve the health of the animal.

Gustavo Cruz

Bethany Oglesby

The intestine is the physical divider between digesta and the body; damage to this barrier will wreak havoc on the body.

The livestock industry continues to seek ways to maximize production and minimize losses. Supporting gut integrity is an important area to consider to further improve animal performance.

Cattle are subject to a variety of environmental and metabolic stresses known to reduce performance and meat quality.

Stressors include weaning, castration, handling, transportation, feed restriction, heat stress, acidosis and disease.

Stress has been reported to disrupt the intestinal epithelial layer, leading to an increase in gut permeability. Compromised gut integrity allows endotoxin, also known as lipopolysaccharide (LPS), to pass into circulation.

Endotoxin is a glycolipid in the membrane of gram-negative bacteria that has an active toxic domain, lipid A. When the endotoxin enters circulation, it can be deactivated by binding to acute phase proteins, or immune, liver or splenic cells.

However, an elevated concentration of circulating endotoxin can induce local and systematic inflammation and further affect gut integrity and nutrient absorption.

The gut is heavily populated with gram-negative bacteria, making the gastrointestinal tract the primary source of endotoxin.

Moreover, endotoxin is released during bacterial cell growth, division and death, making endotoxin a pervasive molecule. Endotoxin can pass through the intestinal wall into circulation through transcellular, receptor-mediated endocytosis, or paracellular, through cell tight junctions, transport.

Endotoxin translocation and subsequent inflammation have been linked to immune system activation and reduced appetite, feed efficiency and performance.

Energy and nutrients are partitioned away from lean tissue accretion to meet the needs of the immune system. In addition, nutrient absorption has been shown to be impaired under prolonged immune or metabolic stress.

The decrease in sugar and AA absorption only exacerbates the problem, leading to the breakdown of muscle proteins to support gluconeogenesis for the increase in metabolic demand from the immune system.

One study estimated a 30 percent increase in energetic cost from endotoxin-associated inflammation resulting in a negative nitrogen balance from protein degradation.

Research has shown that the processes of weaning and transportation of beef calves increase acute phase proteins, indicating an immunological response.

Furthermore, acute phase protein concentration has shown to be reduced in early weaned calves compared to normal weaned calves when stressed by transportation.

When given an endotoxin challenge, early weaned calves appeared to have a more competent immune response compared to normal weaned calves.

This research shows the benefits of weaning early before shipment to strengthen the animals’ ability to cope with stress- induced inflammation and thus improve feedlot performance.

Castration is another stressful event that can impact animal performance. It has been shown that weight loss increases as the age of castration increases.

The weight advantage of postponing castration till after puberty is diminished by the weight loss associated with castration in the finishing period. Therefore it is advantageous to castrate close to birth over after puberty to minimize stress and weight loss.

Grain-induced subacute ruminal acidosis has been shown to increase ruminal endotoxin concentration, stimulate an immune response and cause the translocation of endotoxin into the circulation of cattle.

Maximizing performance and avoiding health crashes is challenging; understanding the thresholds of acidosis-induced endotoxemia could aid in preventing performance losses.

There is nutritional research that offers potential solutions to reduce gut permeability. In pigs, n-3 polyunsaturated fatty acids have been shown to reduce endotoxin transport while saturated fatty acids increase endotoxin transport.

Supplementation of amino acids, such as arginine and glutamine, has been shown to reduce gut permeability under exercise- induced heat stress for mice and humans, respectively.

Oats supplementation has been reported to prevent alcohol-induced gut permeability in rats by preventing oxidative tissue damage. In addition, zinc supplementation has been found to aid gut integrity in diseased patients and rats.

Further research and better understanding of the regulation of gut integrity and endotoxin are needed to develop nutritional and managerial recommendations to combat the detrimental effects of stress and endotoxin on animal performance and enterprise profitability.