Veterinarian’s Corner: Enhancing Gut Immune Function to Prevent Calf Respiratory Disease

By Dr. Jenn Rowntree, Vita Plus calf and heifer specialist
The past two years have both been wet years in the record books compared to normal. Wet weather and temperature fluctuations, especially during spring and fall, are associated with an increased risk for bovine respiratory disease (BRD) in cattle of all ages. In National Animal Health Monitoring System data from 2007, BRD was the leading cause of death in post-weaned heifers and the second-most common reason for death in preweaned heifers. In 2011, Dr. Alex Bach showed both days in milk and productive life decrease with an increased number of respiratory treatments during the rearing period. These factors, combined with the cost of antibiotic treatments and reduced growth efficiency, are reasons to reduce overall prevalence of BRD within herds.

In addition to prompt identification and treatment of sick calves, consider evaluating aspects of your current calf program that contribute to overall immune function in the gastrointestinal tract (GIT) of young calves. Think of the gut as not only the major site for a potential invasion by disease-causing pathogens, but also as the main line of defense from the outside world.  Cells in the GIT sound the alarm when pathogens break past the intestinal barrier and respond to attacks when necessary while simultaneously distinguishing between beneficial and harmful bacteria.  The following are strategies that can help boost GIT health and function.

Optimize colostrum and maternity management
The importance of colostrum cannot be overstated, not only as a source of immunoglobulins from dam to calf, but also as a critical component to establish the gut microbiome. Measuring serum total protein (STP) levels in calves that are 1 to 7 days old remains the most useful on-farm strategy for evaluating effectiveness of the maternity and colostrum program. One large study showed that calves with STP values less than 5.7 grams per liter were 1.6 times more likely to experience BRD in the first five weeks than calves with higher STP values. In fact, 21% of the BRD cases in this study potentially could have been avoided with successful passive transfer in affected calves.

Along with timely administration of colostrum (4 quarts within four hours of birth), ensure the calving environment is as clean as possible. A study published in 2016 by Lima et al. compared calves that developed BRD within the first two months of life with healthy calves.  As early as three days of life, the BRD calves had higher bacteria loads in their upper respiratory tracts than the calves that remained healthy.  This indicates that early exposure to bacteria can have lasting disease implications.

Minimize scours
Calves that experience diarrhea and other diseases before day 14 are more susceptible to respiratory tract infections in the ensuing period. The exact mechanism behind this connection remains unclear and is most likely multifactorial. Calves with diarrhea in the first seven to 14 days of life also have altered intestinal permeability compared to calves that do not experience scours. In addition, calves with scours often experience a shift in the normal beneficial bacteria that reside within the gut. Reduced microbial diversity and altered intestinal permeability can allow for movement of harmful bacteria and their toxins from the outside world (i.e. in the intestines) into the body, where they are sensed by lymphoid tissue that send signals to the immune system. An appropriate immune response, stimulated by a healthy microbiome, will lead to elimination of the invading pathogen. An overreaction can lead to inflammation, not only within the gut, but also systemic inflammation at different mucosal sites in the body, such as the upper respiratory tract.

Reduce stress
Potential sources of stress for calves include changes in social groups and diets, transportation, inadequate feed or water access, illness, extreme temperatures, vaccinations, and procedures such as dehorning and castration. When stress is perceived, it promotes a feedback cycle that allows for the release of cortisol and then pro-inflammatory immune signaling cells. In the gut, this can cause the breakdown of tight junctions that form a tight bond between the cells lining the intestine. Just like calves with scours, this “leaky gut” phenomenon increases the risk that bacteria and their toxins can enter the bloodstream.

The link between stress, the microbiome of both the GI and respiratory tracts, and overall health and immune status of cattle continues to be explored. For now, taking the time to ensure your farm has management practices in place to properly set up a newborn calf’s immune system will not only benefit the individual calf, but also help protect the future of your herd by improving overall herd immunity.