Milk weights, calving intervals, pregnancy rates: Metrics are everywhere on a dairy. But, unlike other aspects of dairy management, there is no clear way to evaluate a cow’s immune function. Yet, a strong immune system is vital for dairy health and performance. Without it, pathogens win.
Under ideal conditions, the immune system maintains a stable, healthy internal environment known as homeostasis. Under this ideal environment, the cow’s bodily functions work in harmony to resist outside dangers and keep systems working at peak efficiency.
Problems occur when this balance is disrupted, often due to animal stress. An overactive immune system causes inflammation that robs cows of energy and overworks their organs. But, if the immune system doesn’t work hard enough, pathogens can invade. The key is balance.
For optimal immunity, it’s important to strengthen the animal’s defense mechanisms rather than targeting a specific disease agent. With strong immunity, cows can fight a variety of challenges, and nutrition plays a key role.
Strengthen the barrier
Developing the immune system inside the cow starts by building a strong defensive barrier in the gut. The first immune component of the gut is the mucin barrier. A healthy mucin barrier protects gut lining cells against up to 90% of challenges. It’s important to realize that this barrier is not a static wall but an immunological organ that is ever-changing and evolving.
The mucin barrier consists of four components. The first three make up what is called the “kill zone,” where pathogenic bacteria are identified and attacked. Here are the major functions of each of the four components of the barrier:
- Mucous production. Goblet cells produce mucus that holds antibodies and other materials to protect against harmful pathogens. It also provides a matrix for organisms to grow in.
- Anti-microbial peptides. These are produced by normal bacteria in the gut and are the body’s natural bacteriocins to will kill bacteria considered pathogenic.
- IgA: Transports specific microorganisms across the barrier to attack foreign organisms.
- Tight junctions: Space between cells that make up the barrier. The tight junctions keep cells together so harmful cells can’t get through. Inflammation causes the junctions to relax and cells to separate. This condition is often referred to as “leaky gut.”
Managing the barrier is important to keeping the immune system in balance. Commensal bacteria, natural inhabitants of the gut outside the cell walls, produce various compounds. These cross the barrier to create anti-inflammatory hormones that keep the immune system from overreacting.
Outside factors can affect immune system response to attacks – especially when animals are under stress. Any environmental stressors – off-feed, dehydration, diet changes, heat stress, pen movements, etc. – can deplete the kill zone and reduce commensal bacteria. As a result, harmful bacteria can penetrate the barrier and inflammation can go unchecked, leading to potential issues like leaky gut.
While a poorly functioning immune system can allow pathogens to cause harm, an over-responsive immune system can cause harm as well in the form of too much inflammation. Viruses like bovine respiratory syncytial virus (BRSV) are adept at putting the immune system into hyperdrive and creating inflammation inside the lungs, which leads to respiratory issues. Excess inflammation also impacts the liver and reduces its function. This activity can reduce feed intake and milk production and lead to mastitis and metritis.
To bolster the immune system, first take steps to avoid inflammation. Reduce stressful situations whenever possible, keep animals properly hydrated and avoid ramping up cows on rations that are too highly digestible. It’s also helpful to feed probiotics to help cows navigate stress and reduce risk.
Feeding for stronger immunity
Research on the impact of feed ingredients on immunity has identified probiotic ingredients that bolster immune function. For example, refined functional carbohydrates (RFC) improve the function of the barrier and help improve gut integrity. RFCs prevent pathogens from binding to the cell wall by agglutinating them, or forcing them to stick together, so they can’t cross the kill zone of the barrier. RFCs also strengthen the kill zone and barrier, so pathogens are not able to attach, colonize and replicate. This indirect effect supports the animal’s ability to prevent pathogens from doing harm.
Feed ingredients containing specific strains of Bacillus subtilis also help improve immunity. Traditionally, Bacillus subtilis are used to target toxigenic and non-toxigenic clostridia. Recent research in poultry1 shows that certain strains of Bacillus subtilis also can increase the proteins responsible for maintaining tight junctions between cells, thereby improving gut integrity.
In summary, when the immune system is in balance, cow performance and the ability to ward off disease improve. Animals use energy toward performance rather than immune function, especially as it relates to inflammation. By strengthening the kill zone and protective barrier, and maintaining a strong junction between cells, cows can build defenses against a broad spectrum of pathogens.
References omitted but are available upon request by sending an email to the editor.
