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Enhance immune function to prevent calf respiratory disease

Jenn Rowntree for Progressive Dairy Published on 31 October 2019

Bovine respiratory disease (BRD) in both pre- and post-weaned calves can be a major challenge. The latest National Animal Health Monitoring System (NAHMS) study conducted in 2014 found 11.3% of enrolled pre-weaned dairy calves showed clinical signs of BRD, of which 88% were treated with an antibiotic.

Unlike scours, which typically occurs in the first two weeks of life, BRD tends to occur later in the pre-weaning period, around 5 weeks old or during the post-weaning phase.

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In the NAHMS data from 2007, BRD was the leading cause of death in post-weaned heifers and the second most common reason for death in pre-weaned heifers. In 2011, Dr. Alex Bach showed that days in milk and productive life decrease with an increasing number of respiratory treatments during the raising period. These factors, combined with the cost of antibiotic treatments and reduced growth efficiency, are reasons to reduce overall prevalence of BRD within herds.

Control and treatment of BRD in young calves is complicated. This disease is impacted not only by the pathogens which cause the disease but also by immune function status, environmental factors such as weather and season of birth, and facilities in which calves are raised. New buildings designed for adequate ventilation and air quality, proper stocking density and smaller group sizes, cleanliness and herd-specific vaccination programs all have made positive movements toward reducing incidence of BRD.

However, even the best facilities, weather and vaccine programs cannot guarantee total protection from the milieu of viruses (IBR, BRSV, PI3) and bacteria (Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Mycoplasma bovis) that have been identified as players in this complex disease. Thus, some calves still succumb to BRD. What else can be done?

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 the young calf. Think of the gut as not only the major site of 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. Colostrum contains commensal microbes that will help establish a population of healthy bacteria in the gut as well as oligosaccharides that act as a food source to feed beneficial bacteria acquired from the environment. A calf’s gut microbiome is established within the first 12 to 24 hours of life and plays a key role in metabolism, immune function and, therefore, overall calf health.

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Measuring serum total protein (STP) levels in calves 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 calves with STP values less than 5.7 grams per liter were 1.6 times more likely to experience respiratory disease 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 litres within four hours of birth), ensure the calving environment is as clean as possible. A study published in 2016 compared calves that developed BRD within the first two months of life with healthy calves. At 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 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 have altered intestinal permeability compared to calves that do not experience scours. Interestingly, this increase in intestinal permeability was detected within the first two hours of life, well before calves showed clinical signs of diarrhea. It is uncertain as to the exact reasons for inherent differences in intestinal permeability between calves soon after birth, but potential influencing factors include colostrum quality and timing of administration, genetics and establishment of the calf’s microbiome early in life.

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 sends 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, or the uterus and mammary glands in mature cows.

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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.

Immune function is suppressed by cortisol, which reduces the body’s ability to fight off (real or perceived) threats. When stressed, a calf is most susceptible to infection from bacteria or their toxins that may typically reside in the GIT or upper respiratory tract. For example, Mannheimia haemolytica is a normal inhabitant of the nasopharynx, but it can also lead to BRD when calves are exposed to stress or another pathogen like Mycoplasma bovis.

Once engaged, the immune system demands a tremendous amount of glucose to adequately respond. This not only draws calories consumed in the diet away from growth but also can rapidly deplete vitamin and mineral stores needed for immune function.

The link between stress, the microbiome of both the GIT 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.  end mark

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

Jenn Rowntree
  • Jenn Rowntree

  • Dairy Calf and Heifer Specialist
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