Respiratory Sampling in Cattle

The Bovine Respiratory Syndrome (BRS) is one of the most common infectious diseases in young calves.

It is characterized by the simultaneous involvement of viral and bacterial microorganisms, and there are certain predisposing factors that favor its appearance, such as the immune status of the individual or certain environmental conditions or managements that cause stressful situations (transport, high animal density, etc.).

ETIOLOGY OF BRS

The main viral and bacterial agents involved in BRS are shown in Table 1 .

In general, viruses act as primary agents that damage the pulmonary epithelium and respiratory tract mucosa, favoring the proliferation of respiratory bacteria that trigger the severe clinical condition.

APPROPRIATE SAMPLES FOR BRD DIAGNOSIS

To obtain a reliable laboratory diagnosis, one of the key aspects is the sampling.

It is necessary to correctly select the animals for sampling and ensure that the sample is properly preserved until its reception in the laboratory.

Depending on the availability and analysis objective (diagnosis of a clinical case or farm monitoring), different types of samples can be sent (Figure 1).

SAMPLING PROTOCOLS

Before starting sample collection, it is essential to have the material prepared and a standardized sampling protocol to carry out the sampling in a systematic and organized manner.

Lungs

Fragments from different areas should be collected when different macroscopic lesions are observed.

Samples should be collected with the greatest asepsis possible to avoid contamination using a sterile scalpel and placed in a sealed jar or bag.

It is also advisable to take the sample from the interior of the lung parenchyma with a swab and place it in a preservation medium, as environmental bacteria can proliferate over time and the tissue may undergo autolysis, altering the laboratory study.

BOVINE – Lung Necropsy
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Bronchoalveolar Lavages

After properly restraining the animal, the probe is inserted through a nostril and, upon reaching the lower respiratory tract, a variable volume of saline solution is introduced depending on the size of the animal (20-40 ml) and immediately aspirated, collecting the maximum amount of serum possible.

It is important to continue aspirating while withdrawing the probe to also obtain a sample from the trachea. The lavage is then transferred to a sterile tube and identified with the animal’s ear tag.

BOVINE – Bronchoalveolar lavage
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Transtracheal washes

To collect this sample, it is necessary to have a good restraint of the animal and administer sedation, being important to shave and disinfect the access area to the inside of the trachea.

The area between two tracheal rings as caudoventral as possible is located and accessed with the trocar, then the catheter is inserted through the trocar and saline is introduced (the amount depends on the size of the animal) and immediately aspirated, collecting the maximum amount of saline possible.

It is important to continue aspirating while removing the catheter. Then the lavage is transferred to a sterile tube and identified with the animal’s ear tag.

Deep Nasal Swabs

After properly restraining the animal, the long swab with plastic protection is inserted through a nostril, upon reaching the retropharyngeal area, the swab is exposed from the protection, swabbing is performed on the mucosa of the area, and it is reinserted into the protection to remove it through the nasal passages, avoiding contamination with commensal bacteria from the upper airways.

Once outside the animal, the swab is placed in a tube with preservation medium, ensuring that the swab is inside the medium and is identified with the animal’s ear tag.

BOVINE – Nasal Swab
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Serums

The extraction of blood serum is performed with blood tubes without anticoagulant that are left at room temperature to allow clot formation. Subsequently, the serum is separated in an Eppendorf tube for blood serum analysis.

Environmental sample

The diagnosis of environmental samples is aimed at monitoring diseases present in livestock.

Respiratory pathogens are transmitted via airborne routes, making it possible to conduct an air sampling to assess the circulation of respiratory infectious agents in the environment of the facilities.

ADVANTAGES, DISADVANTAGES, AND LIMITATIONS OF DIFFERENT TYPES OF SAMPLES

Lungs 

Allows for a complete diagnosis.
Assessment of respiratory problems in lower airways.
Requires recently deceased or slaughtered animals.
As it is a limited number of samples, it may not be representative of the group’s problem.

Bronchoalveolar lavages 

In vivo sampling.
Allows sampling of a larger number of animals.
Provides information on the agents present in the lung.
Requires specific equipment and qualified personnel.
Risk of presence of commensal bacteria in nasal cavities.

Transtracheal washes

In vivo sampling.
Allows sampling of a larger number of animals.
Provides information on the agents present in the lung.
Requires specific equipment and qualified personnel.
It is a more invasive technique for the animal.

Deep nasal swabs

Easy to take from live animals.
Allows sampling of a larger number of animals.
Assessment of respiratory problems in upper airways.
No lung sample is obtained, only reaches the retropharyngeal area.

Serums

Good monitoring system through seroprofile creation.
Simple sampling of animals.
Incomplete diagnosis limited to diseases for which serological kits are available.
A significant number of animals must be sampled to obtain conclusive group results.
It is an indirect diagnosis, analyzing the presence of antibodies in response to the infectious agent, not the pathogen itself.
In most diseases, it is not possible to differentiate the response to a vaccine from the response to natural infection.

Environmental sample

Airborne disease monitoring system.
Simple sampling.
Requires specific material.

LET’S DIG DEEPER: WHAT IS THE BEST SAMPLE?

As we have previously mentioned, there are different types of samples.

So, which is the best?

The Table 2 presents the most suitable samples based on the sampling objective.

CONCLUSIONS

The BRD is one of the main pathologies in cattle and, depending on the animals available and the diagnosis to be made, the most appropriate samples will be chosen:

The lung samples offer the most comprehensive diagnosis, but they are postmortem and not very representative at the group level.

The bronchoalveolar and transtracheal washes are useful and specific for pulmonary agents, but require specialized technique and equipment.

Nasal swabs are easy and useful for upper airways, although they do not allow detection of pulmonary agents.

Serum is ideal for group monitoring, although it offers an indirect diagnosis.

Environmental samples provide an overview of airborne pathogens, with low impact on the animals.

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