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Listen to your gut

Vanessa Riddell for Progressive Dairy Published on 19 October 2020

As a passionate farmer, you do everything you can to keep calves looking and performing their best. But what if one of the greatest opportunities to support calf health is something you cannot visually see?

To stay alive, animals and humans have developed what we are now exploring as an incredibly complex and dynamic immune system in the gastrointestinal tract (GIT). In total, 70% or more of a calf’s immune system is located in the gut. So, yes, we care about gut health and we absolutely care about what contributes to a healthy gut in terms of genetics, maternal influence during gestation, diet, level of nutrition, feed additives, etc.



A calf’s gut microbiome includes bacteria, fungi, viruses and more than 13 trillion microorganisms that are both beneficial and detrimental to calf health. When the bad outweigh the good, calves are at a higher risk for health problems. So what’s the secret to keeping a balanced gut? Let’s “gut” into it.

You may be familiar with the term “leaky gut syndrome.” What does this mean, and why do we care? An inflamed gut is a leaky gut. Various physiological stressors can cause inflammation, and it is not limited to infection. For instance, did you know that heat stress will indirectly cause inflammation in the gut? In order for a calf to cool off, the body will work to send blood away from internal organs toward the extremities, lowering core temperature.

In doing so, the calf’s internal organs enter into a pseudo-hypoxic state, a fancy term for lack of oxygen, which makes sense; as blood leaves, so does oxygen. About 30% of daily energy requirements travel to the gut, so for a high-powered organ system, any reduction in available oxygen is a problem. Pair this with reduced feed intake during heat stress, and the cells of the gut become quite compromised with no food and no air. As a result, cells are weaker and dehydrated, causing the tight junctions between epithelial cells (the barrier between the inside and outside of a body) to begin to break down, hence, the term “leaky gut syndrome.”

During this compromised state, signals are being sent to prompt the immune system for help. The mucosal layer is also thinned, reducing the physical barrier from the intestinal lumen to the epithelial cells. This is bad news, as pathogenic bacterial toxins can now enter the bloodstream and further amplify inflammatory and immune responses, taking more energy away from growth. In addition to heat stress, these factors follow a similar mode of action that may lead to an inflamed gut and subsequent damage: weaning too abruptly, social mixing, disrupting meal times, changing feed, acidosis and maternal stressors experienced in late gestation.

Now that we understand what an inflamed gut is and its corresponding effects, how can we create and maintain a healthy gut environment? What you feed plays a vital role in how the gut ecosystem thrives or dies. Colostrum is an absolute requirement for a successful start; the first meal provides immunoglobulins for immune protection and an easily digestible source of energy. Beyond immunity and energy, colostrum also contains growth factors and complex milk carbohydrates (such as galactooligosaccharides [GOS]), which stimulate nutrient uptake, cell growth and integrity, and promote the early establishment of a healthy gut microbiome.


Heat-treating colostrum increases the advantages of GOS, which amplifies the colonization of probiotic bacteria, and in turn, potentially reduces the development and severity of scours caused by pathogens. Extending colostrum feeding beyond day one, in addition to feeding transition milk, will provide the calf with continuous exposure, flow of nutrients and bioactive components to protect, build and support the local immune system in the gut and the gut itself.

How do feed additives (bioactives) contribute to gut health? In the first seven days of life, calves will develop a full army of gut defenses, including establishing tight junctions and a mucous layer – the first real physical defence for the gut. It appears that the first couple hours of birth is the most important time to “seed” the GIT with beneficial bacteria, although which species and in what proportion is not known. To help maintain healthy gut symbiosis, there are many additives that can be used in a formulation to support healthy gut development.

1. The first additive to consider is a prebiotic. Common products include mannan oligosaccharide (MOS) from yeast and GOS from colostrum and transition milk. These complex carbohydrates act like mops in the gut; when certain bacteria invade, MOS will bind to the receptor on the bacteria, preventing it from attaching to the gut cell. Beta-glucans (yeast cell walls, barley, oats) stimulate immune cells by being able to find a variety of receptors and initiate signaling pathways for an immune response.

They are also a form of soluble fibre, creating a fibre matrix in the gut, slowing transit time. Another common prebiotic is resistant starch, which is not digested by animal enzymes but is fermented by good bacterial populations, generating volatile fatty acids (VFAs) as byproducts. These VFAs are then fuel for the epithelial cells of the gut. Prebiotics can support the immune system as food for probiotics, but not all pre- and probiotics are equal. There are different strains and types; each act differently in the gut.

2. Probiotics are extremely beneficial to optimizing gut health. Probiotics are live, beneficial microorganisms, including bacteria or yeast. They help support a healthy microbiome by colonizing the gut to outcompete pathogenic bacteria, making the environment hostile for bad bacteria. It is not known what types of probiotics are the best, as this will depend greatly on the host animal’s current microbiome, but probiotics will improve the calf’s nutrient utilization and supports overall immune function.

3. Plant essential oils can have a targeted effect on gram- negative bacteria – for example, E. coli – but less effect on gram positives, such as Lactobacillus, the good guys. The mode of action is to disrupt cytosolic pH, causing the bacteria to take on more water, swell and either slow in growth or rupture and die.


4. Electrolytes and osmolytes maintain cellular hydration, especially epithelial cells in the gut. When dehydrated, gut cells contract, spend more energy trying to correct ion gradients and tight junction and cell strength is weakened. Betaine is very effective in maintaining cellular hydration.

Feed additives play a vital role in supporting a healthy gut, but also remember the importance of choosing a milk replacer that complements your feeding practices, the housing system and that delivers consistent quality. Both the feeding schedule and the milk replacer must provide the necessary requirements to develop and repair the gut.  end mark

PHOTO: Photo by Mike Dixon.

References omitted but are available upon request. Click here to email an editor.

Vanessa Riddell
  • Vanessa Riddell

  • Young Animal Specialist
  • Grober Nutrition
  • Email Vanessa Riddell