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Bovine Respiratory Disease Juan Vicente González Martín Natividad Pérez Villalobos

Bovine Respiratory Disease This book is a comprehensive review of the Bovine Respiratory Disease, a condition that causes significant economic losses on cattle farms. It is divided into 16 chapters, in which important aspects such as the epidemiology, predisposing factors, main pathogens involved, diagnosis, prophylaxis and treatment of the disease, among other specificities, are addressed. In the book “Bovine Respiratory Disease”, veterinary professionals will also find a great collection of images and a practical chapter with examples of how some real clinical cases were solved.

Juan Vicente González Natividad Pérez Villalobos

Bovine Respiratory Disease

Bovine Respiratory Disease

Thanks to the authors’ broad experience in the fields of research and education, this work contains updated information about this disease, whose scientific validity has been established, and is written in a structured way, with a clear didactic style that makes it easy to read.

Juan Vicente González Martín Natividad Pérez Villalobos

Bovine Respiratory Disease

An indispensable book for all the veterinary professionals whose work focuses on cattle.

Authors: Juan Vicente González and

Natividad Pérez Villalobos.

Format: 17 x 24 cm.

Number of pages: 192.

Number of images: 239.

Binding: Hardcover.

eBook included

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This book is a comprehensive review of the bovine respiratory disease (BRD), a condition responsible for significant economic losses in cattle farms. The book is divided into five chapters, which address important aspects of the disease, including epidemiology, predisposing factors,the main pathogens involved, diagnosis, prophylaxis, and treatment.

The final chapter is a compilation of actual clinical cases. Thanks to the authors’ broad experience in the fields of research and education, this work contains up-to-date, scientifically validated information on BRD. Its structured format and clear, didactic style facilitate reader comprehension. All told, this is an indispensable book for veterinary professionals who work with cattle.

Bovine Respiratory Disease

Presentation of the book In beef cattle, stockmen and practitioners are fully aware of the importance respiratory diseases have. This is due to the fact that bovine respiratory disease is the main cause of morbidity and mortality in feedlots. The loss of productivity secondary to cronically affected animals, lower average weight gain, longer stays in feedlots, confiscations at slaughter, etc., is also well documented. Thus, both prophylactic measures targeted to BRD control, as well as correct design of facilities, appropriate management practices, vaccination programmes and antimicrobial and symptomatic therapeutic approaches are also well known.

In the case of dairy cattle, this awareness on BRD importance is not established this way.

There is a tendency to understate the problem and consider this condition as a sporadic disease. Which would be the reason? It may be multiple. On the one side, this can be due to the fact that in herd health and production medicine we don’t pay as much attention to replacement as to other aspects like milk quality, reproduction or hoof care. On the other side, it may be because in these programmes, little attention is payed to classic medicine, specially when compared to other productive data, indices or costs.

In this book, the authors have carried out a thorough and updated review of the disease, from its incidence to its economic importance, both in beef and dairy cattle, to the analysis of all factors- microbial, environmental and animal dependent- involved in the development of BRD.

The authors Juan Vicente González Martín PhD in Veterinary Medicine (2003) from the Faculty of Veterinary Medicine of the Complutense University, Madrid, with a diploma from the European College of Bovine Health Management (2004). He is also Professor of Animal Medicine and Surgery at the Faculty of Veterinary Medicine of the Complutense University, Madrid. He is the manager of TRIALVET, a veterinary consultancy and research organisation, and one of the founder partners of the Spanish Association of Specialists in Bovine Medicine (ANEMBE).

Throughout his professional career, he has conducted several studies focused on the bovine sector. He has authored numerous scientific articles as well as several books, and is a frequent speaker at congresses, courses and seminars on ruminants.

Natividad Pérez Villalobos PhD in Veterinary Medicine (2015) from the Faculty of Veterinary Medicine of the Complutense University, Madrid. She obtained her Master’s degree in clinical trials from the University of Seville, and has completed several courses on management and project management. Currently a researcher and clinical trial supervisor at TRIALVET, a veterinary consultancy and research organisation, she also works as a translator and writer for the ANEMBE bulletin, and collaborates with the Department of Animal Medicine and Surgery at the Faculty of Veterinary Medicine of the Complutense University, Madrid. She has authored numerous scientific articles and books, and has collaborated and participated as a speaker in various congresses, courses and seminars.

Bovine Respiratory Disease

Collaborators Cristiana Isabel Teixeira Justo A graduate of the degree and Master’s programs in Veterinary Medicine at the Biomedical Sciences Institute of the University of Oporto, she also holds a degree in zootechnic engineering from the University of Trás-os-Montes and Alto Douro. She is specialised in dairy cattle and has headed the sampling and milk quality service at TRIALVET, S.L. since 2012.

She is a frequent collaborator with the Department of Animal Medicine and Surgery at the Faculty of Veterinary Medicine of the Complutense University, Madrid.

Raquel Patrón Collantes A graduate in Veterinary Medicine from the Complutense University, Madrid, she currently works at TRIALVET, S.L., where her primary responsibility is milk quality and reproductive consulting, and as a translator and writer for the ANEMBE bulletin. She is a frequent collaborator with the Department of Animal Medicine and Surgery at the Faculty of Veterinary Medicine of the Complutense University, Madrid.

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Juan Vicente González Natividad Pérez Villalobos

Bovine Respiratory Disease

Bovine Respiratory Disease Juan Vicente González Martín Natividad Pérez Villalobos

Table of contents 1. Introduction

4. Treatment and prevention

BRD: definition and synonyms

Treatment of BRD

Incidence, morbidity, mortality and economic importance

Prevention of BRD

2. Aetiopathogenesis Epidemiological triad The host Environment/stress Main pathogens involved in BRD

BRD: pathological classification of pneumonia Interstitial

Vaccination Metaphylaxis

5. Resolution of clinical cases: practical examples BRD caused by M. haemolytica in stocker calves at feedlot entry BRD caused by P. multocida during rearing

Bronchopneumonia

Outbreak of interstitial pneumonia

Other pneumonias

Outbreak of M. bovis in a poor quality lot

Upper respiratory tract problems Evolution

3. Diagnosis Clinical diagnosis of BRD Diagnosis of BRD in individual animals Diagnostic protocols in the herd Differential diagnosis of BRD

Aetiological diagnosis Sampling Laboratory methods

Pathological diagnosis Necropsy Presence or absence of lesions

Epidemiological diagnosis

Acute respiratory distress syndrome (ARDS) Embolic pneumonia due to thrombosis of the posterior vena cava

Aetiopathogenesis

Epidemiological triad

Epidemiological triad The host

Anatomy of the bovine respiratory apparatus The main anatomical features of the respiratory system of cattle are the presence of a longer tracheobronchial tree than other similar domestic species, and smaller lungs in relation to body size.

Like in other domestic animals, the trachea is divided into two primary bronchi that lead to each lung. These in turn are divided into secondary bronchi, which ventilate the lobes of each lung (Fig. 1).

The left and right lobes of bovine lungs are clearly demarcated. Four lobes can be distinguished in the right lung; cranial, middle, caudal, and accessory lobes. The cranial lobe in turn is divided into cranial and caudal parts. Each lobe has its own secondary bronchus, except for the cranial lobe, which is fed by a so-called tracheal bronchus (Fig. 2), which stems from the trachea above the bronchial bifurcation.

The left lung is divided into only two lobes; middle and caudal. The middle lobe, like the right cranial lobe, is divided into cranial and caudal parts (Fig. 3).

The secondary bronchi branch into tertiary bronchi, which carry air to the bronchopulmonary segments, which in turn subsequently divide into lobules (Fig. 4). Like the lobes, the lobules are well demarcated by connective tissue, which is contiguous with the surface of the pleura. Interlobular septa surround each

Figure 1. Dissected trachea and primary and secondary bronchi.

2

Figure 2. Tracheal bronchus (arrow).

Right Left

Figure 3. Pulmonary lobes.

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bronchopulmonary segment individually, limiting collateral ventilation and movement between adjacent segments. For this reason, the bovine lung is considered highly compartmentalised.

■■

The tertiary bronchi lead to the bronchioles, which, unlike the aforementioned structures, lack cartilage. The bronchioles further divide into the terminal bronchioles, which lead to the alveoli.

Physiology of the bovine respiratory apparatus Respiratory physiology

often introduced into the tracheal bronchus.

For this reason the right cranial lobe of the cow is always the first and most severely affected by pneumonic processes.

The extreme compartmentalisation of the bovine lung at the levels of the lobes and the lobules results in negligible movement of air between different parts of the lung. This has an important beneficial effect, as lung infections that begin in the alveoli or lobules cannot spread to other parts of the lung.

However, this physiological peculiarity also prevents air movement between different

In addition to respiration, the respiratory system of cattle performs other important functions including thermoregulation, maintenance of acid-base balance, and several olfactory, immune, and metabolic functions, such as inactivation of prostaglandin F2α.

Moreover, the respiratory system displays several peculiarities that influence its function: ■■ Due to the size and length of the system, it has a large volume and a high percentage of dead space as compared with the respiratory systems of other domestic animals, including horses. This dead space affects the volume of oxygen that reaches the lungs, increases the risk of problems such as pulmonary hypoventilation and partial obstruction, and can even facilitate the deposition of particles along its entire length. The expulsion of these particles, as well as toxic vapours and gases, requires greater effort due to the length of the respiratory system (Fig. 5).

■■ The tracheal bronchus is located above the bronchial bifurcation (Fig. 2). Particles or bacteria expelled by the mucociliary barrier, while either ascending or descending, are

Figure 4. Pulmonary lobules: marked lobular structure.

Figure 5. Length of the bronchial tree.

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Aetiopathogenesis

■■

■■

■■

■■

parts of the lungs and can lead to disorders such as emphysema.

The lack of communication and pressure equalisation between the different parts of the lung is further complicated by the fact that there is little communication between individual alveoli, owing to their low numbers of Kohn pores.

As mentioned above, the bovine lung is very small in proportion to body size, and during normal breathing the tidal (or pulmonary respiration) volume of each breath occupies almost the entire capacity of the lung, leaving very little reserve volume.

The normal breathing pattern is costo-abdominal. Any alteration will induce a change in the breathing pattern, as evidenced by a thoracic breathing pattern in the presence of abdominal pain (e.g. peritonitis), or an abdominal pattern in the presence of thoracic pain (e.g. pleuritis). Respiratory difficulties are known as dyspnoea.

For the sake of reference, the bovine lung is about three times smaller than that of a similar sized horse. However, owing to their

Increases in respiratory frequency and depth (tachypnoea or polypnoea) can occur in cases of metabolic acidosis or in conditions of high humidity or high temperature, as thermoregulation in cows is mediated by the respiratory system.

By contrast, diminished respiratory frequency and depth (bradypnoea) is observed in the presence of thoracic or abdominal pain and in cases of metabolic alkalosis.

Epidemiological triad

metabolism, a cow’s oxygen consumption is 2.5 times that of a horse. Cows thus have a higher respiratory rate, ranging from 15 to 35 bpm or 18 to 28 bpm, depending on the study. This rate can be altered by several factors, especially the ambient temperature, although others include pregnancy, increased digestive volume (mainly rumen volume), body size, exercise, excitation, and age (younger animals have a higher respiratory rate of between 20 and 40 bpm).

Classically, tachypnoea is categorised as inspiratory in cases involving alterations of the upper airways, and expiratory in cases of alterations of the lower airways. In severe conditions, such as pneumonia or narrowing of the tracheobronchial tree, dyspnoea is usually mixed. Breathing sounds that are audible without auscultation usually indicate obstruction of the upper airways. In cases of severe dyspnoea the animal often adopts orthopneic positions, stretching its neck and extending the elbows.

2

Immune physiology The objective of pulmonary immunity is to maintain the sterility of the lungs without inducing inflammation, as this hinders gas exchange. However, it is important to remember that this sterility is not total, as the upper airways, nose, and pharynx contain a variety of bacterial flora, or microbiota, of the genera Bacillus, Streptococcus, Streptomyces, Micrococcus, and Pseudomonas, among others, and even some pathogenic agents such as Pasteurella, Mycoplasma, and Histophilus. These florae most likely compete with pathogens in the upper airways and form part of the innate immune system.

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Traditionally, the lower airways have been considered sterile. However, the microbiota, although found mainly in the upper airways, can be distributed throughout the respiratory system by inspiration.

The main innate defence of the respiratory system, in both the upper and lower airways, is the mucociliary system (Fig. 6). This is a seromucous substance that covers the ciliated epithelial surface of the airways. It is arranged in two distinct layers: a liquid layer that covers the epithelium of the respiratory apparatus, and a superficial gelatinous layer to which foreign particles adhere.

In the upper airways, this mucociliary “escalator” moves in a cranial-to-caudal direction towards the glottis, while in the lower airways it moves upward in a cranial direction. Thus, inhaled particles, depending on their size and the air velocity, are deposited on and adhere to mucus of the airway walls, from which they are removed by the ciliary system and subsequently swallowed. Inertia, defined as the force resulting from the velocity of inhaled air, is the main mechanism by which these particles adhere, and is most important in the upper airways, particularly in the nose.

The larger the particle size and higher the air velocity, the more likely the particle will collide with and be trapped by the nasal turbinates. By contrast, smaller particles normally adhere by sedimentation due to gravity, and do so more easily when the air velocity is lower, which is usually the case in the bronchial region or even in the alveoli.

Highly irritating products (e.g. gas and some types of dust) can cause violent reactions such

as coughing, sneezing, or apnoea, provoking more rapid expulsion of the particles.

Mucociliary clearance of these particles, as well as microbes and toxic gases, especially if soluble, will depend on their location. Clearance times are much higher in the upper airways and decrease progressively along the lower airways, with an average clearance time of about 2 to 6 hours.

The presence of innate defence proteins in the mucociliary system serves to limit bacterial growth during clearance. Furthermore, because the transport velocity depends largely on the viscosity of the secretions, the degree of hydration is also very important. The rate of mucociliary transport is diminished by contaminants such as toxic gases (e.g. sulfur dioxide) or smoke, by chronic or acute infections (mainly viral or mycoplasmic), and by direct dehydration of these secretions caused by tachypnoea or very dry environments.

In addition to the mechanical protective function of the mucus and cilia, which collect and remove foreign bodies and microbes, respiratory secretions contain numerous molecules and agents with antimicrobial activity, many of which are produced by Clara cells. These include transferrins and lactoferrins, lysozymes, interferons, interleukins, α1-antitrypsin, complement, and surfactant, which have opsonising properties that facilitate phagocytosis. Other important components of these secretions include proteases, antioxidants, and polymorphonuclear phagocytes.

Secondary and tertiary bronchioles are the most vulnerable, as these are the places with the least

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Aetiopathogenesis

Epidemiological triad

Figure 6. Mucociliary system. Adapted from Ackerman et al., 2010.

Airway

1

Bronchiole

2

Ciliated epithelial cell

B

A

3

Alveoli

Submucosal gland Airway surface liquid

1

H2O2 + SCN-

1

OSCN-

2 Clara cell Type II cell

C

2

2

D

3

Type I pneumocyte

Alpha/beta and gamma/delta T cells; B, NK, NK-T cells

3

Neutrophil

Macrophage

A - Duox Dendritic cell

B- Lactoperoxidase C - Antimicrobial peptides D - Antimicrobial proteins

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mucociliary clearance capacity and have fewer alveolar macrophages. If the microbe finally reaches the alveoli, it will be captured by alveolar and intravascular macrophages.

There are also specific lung defence mechanisms such as the bronchi-associated lymphoid tissue (BALT, which is part of the lung’s immune system), T lymphocytes, and natural killer (NK) cells, which are probably the most effective in defending against viruses, intracellular bacteria, and fungi. As mentioned previously, all respiratory secretions contain antibodies that act specifically against many bacteria, preventing their adhesion to cell receptors, opsonising and agglutinating them to facilitate phagocytosis, and activating the complement system, which destroys them and/or initiates the inflammatory process.

Both the innate and adaptive immune responses can be affected by stress. This may be secondary to an increase in population density, or caused by regrouping (social stress), heat, large temperature fluctuations, gusts of wind, transportation, or other factors such as noise and abuse, as described in the section on stress and the environment. Large amounts of cortisol are released in response to stress, leading to failure of the entire system of cellular responses, both innate and specific.

Primary infections, particular those of a viral nature but including those caused by bacteria in conditions of high stress, trigger an inflammatory response and diminish the innate response of the pulmonary defence system.

them particularly susceptible to respiratory problems, especially BRD. Due to the length of the tracheobronchial tree and the large volume of the upper respiratory airways, the deadspace/tidal-volume ratio is very high; 40 % to 55 % in calves and 75 % in adults. These figures are almost double those of other species, such as dogs and horses. Owing to this high ratio, the risk of hypoventilation and hypoxia in the alveoli is greatly increased when the airways are obstructed.

Pulmonary hypertension Given the ease with which atelectasis can occur, cows have very well developed and powerful smooth muscle fibres in the pulmonary arterioles. If ventilation is reduced in one part of the lung, the other part must alter the distribution of blood and increase flow to compensate for the hypoxic region. The respiratory deficit caused by atelectasis thus triggers vasoconstriction of the pulmonary arteries in order to increase the perfusion of the healthy parts of the lung. This is a beneficial compensatory mechanism. However, severe hypoxia, in which a large portion of the lung is affected, results in widespread pulmonary hypertension which, when chronic, places extra demands on the right side of the heart, giving rise to hypertrophy and dilatation known as cor pulmonale (Fig. 7). This process, which is associated with chronic pneumonia and a high percentage of cases of lung atelectasis, complicates the clinical picture in the medium term due to cardiac insufficiency.

Bronchoconstriction

Respiratory pathophysiology As described previously, the anatomical and physiological characteristics of cattle make

Unlike the bronchi, bronchioles lack a cartilaginous structure and contain muscle fibres, and thus can be more easily occluded. This has

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Diagnosis

Clinical diagnosis of BRD

Diagnosis of BRD in individual animals Traditional methods of identifying sick animals are based on the presence of clinical signs. In the case of BRD, the most common early sign is depression, a nonspecific clinical sign commonly associated with many infectious disease processes. As such, depression is often used to identify potentially diseased animals, with subsequent presumptive diagnosis based on the results of clinical examination, detailed analysis of the clinical history, and inspection of the animal’s environmental and management conditions. However, it should be noted that of all commonly evaluated clinical signs, body temperature is the only objective parameter. While the reliability of other clinical signs may be improved when assessed in conjunction with scorecards or rating systems, they are subjective in nature and depend heavily on the individual performing the inspection.

Figure 1. Calf with signs of depression: the calf is isolated, with its head bowed, and pays little attention to its environment. This is the primary sign of disease.

3

Main clinical signs that point towards a presumptive diagnosis of respiratory disease ■■

■■

■■

■■

■■

General: depression, sunken flanks, and loss of body condition (Figs. 1-3).

Fever: elevated rectal temperature (> 40 °C) (Fig. 4) and coarse hair.

Respiratory signs: rhinorrhoea (rhinitis), epiphora (conjunctivitis), cough, shortness of breath or difficulty breathing, polypnoea or increased respiratory rate (> 40 bpm), mucopurulent nasal discharge, orthopnoeic positions, etc. (Figs. 5-10).

Weakness: leg dragging, flexion (“knuckling”) of the fetlock joint, and lordosis (Figs. 11-13).

Other signs: arthritis, otitis, encephalitis, abdominal distension and bloating (Figs. 14-18).

Figure 2. Sunken flanks are indicative of a poor appetite and an early sign of disease.

Figure 3. The loss of body condition does not occur from one day to the next: it is a sign of a chronic condition.

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Figure 4. Rectal temperature is often the only objective clinical sign of BRD.

Figure 5. Rhinorrhoea (serous nasal secretion).

Figure 6. Epiphora (persistent serous ocular discharge).

Figure 7. Cough.

Figure 8. Calf with dyspnoea (alteration of the normal characteristics of respiration due to breathing difficulties).

Figure 9. In cases of bacterial complications, nasal secretions become mucopurulent.

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Diagnosis

Figure 10. Animals with respiratory failure adopt orthopnoeic positions to facilitate breathing: abducted elbows, extended neck, bowed head, etc.

Clinical diagnosis of BRD

Figure 11. Sick animals show signs of weakness and often drag their limbs when walking.

3 Figure 12. Calf showing flexion of the fetlock of the right hindlimb. This is also a sign of weakness.

Figure 13. Downward curvature of the spine (lordosis) is a sign of weakness.

Figure 14. Inflammation of the right carpus, indicative of arthritis.

Figure 15. Drooping of the ear is a clinical sign of otitis media; in this case, the calf may be suffering from otitis media of the right ear.

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Examination of the respiratory tract and findings associated with the main respiratory diseases

Figure 16. Inclination of the head and abnormal behaviour are signs of encephalitis.

Traditional methods of BRD diagnosis in feedlots do not facilitate accurate diagnosis of the disease (case definition). While the thermometer is the most objective tool, its greatest diagnostic value is in establishing “undetermined fever”, which is of little predictive value. The presence of fever, combined with the analysis of clinical scorecards, can improve the predictive value of the diagnosis. However, conventional medicine attempts to reach a more accurate diagnosis through examination of the respiratory system using tools and techniques such as inspection, palpation, olfaction, auscultation, and percussion (Table 1).

■■

Figure 17. Side view of an animal with chronic ruminal distension. Chronic respiratory disorders are frequently accompanied by chronic ruminal distension caused by difficulties in belching and altered ruminal motility.

■■

■■

■■

Inspection: a detailed examination of the nostrils, conjunctiva, and mouth allows detection of mucosal lesions (Fig. 19). The pattern of lung ventilation of the animal and the rate and type of respiration can also be evaluated. The normal respiratory rate at rest and neutral temperature is 15 to 40 bpm in calves and 10 to 30 bpm in adults.

Palpation: the use of touch to identify the presence of pain or subcutaneous emphysema.

Olfaction: the odour of the breath can provide additional information. Foul-smelling breath may be associated with diseases or the presence of certain bacteria (Fig. 20).

Auscultation: this should be performed in as calm and quiet an environment as possible, taking care to avoid exciting the animal (Figs. 21-25). The entire projection area of

Figure 18. Rear view of a calf with chronic ruminal distension.

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Diagnosis

Clinical diagnosis of BRD

Table 1. Main pathological findings on examination of the respiratory system of cattle.

InspecTIon

The identification of vesicular lesions, lumps, or ulcers in the mucosa can orient the diagnosis towards different diseases. Lesions associated with IBR, mucosal disease, and bovine pseudocowpox are particularly characteristic.

palpaTIon

This technique allows the easy identification of pain (associated with rib fractures) or subcutaneous emphysema.

olFacTIon

Calf diphtheria and gangrenous pneumonia are diagnosed based on the exhalation of foul-smelling air.

Mild disorders with normal respiratory rate.

ausculTaTIon

Alterations that appear erratically.

Increased inspiratory effort.

Increased lung sounds on inspiration due to narrowing of the glottis or trachea, or due to the presence of pulmonary consolidation or atelectasis, which enhances the transmission of bronchial sounds.

Increased expiratory effort.

Increased expiratory sounds due to narrowing of the bronchi, as occurs in bronchopneumonia.

Decreased breathing sounds.

Associated with emphysema due to impaired transmission of sound through the air.

Total absence of breathing sounds.

Associated with pleural effusions and pneumothorax.

Crepitation.

Continuous musical sound typical of chronic atypical interstitial pneumonia and allergic processes that narrow the airway.

Wheezing.

Interrupted bubbling sounds associated with pulmonary oedema and the movement of pus in the bronchi.

Tracheal stridor.

Caused by diphtheria in calves.

Pleural friction rub.

Very rare in cattle.

Tympanic sound.

Associated with pulmonary emphysema and most evident in pneumothorax.

Flat sound.

Occurs in pulmonary congestion, consolidation, atelectasis, and pleural effusion.

percussIon

the two lungs and the trachea and glottis should be auscultated. The phonendoscope should be pressed firmly against on the chest wall. Avoid generating friction against either the bell or the disc as this can interfere with auscultation. It is important to learn to differentiate between superimposed cardiac

3

and digestive sounds. Normal respiratory sounds are at maximum intensity in the glottis and trachea, decreasing in the lung area in cranial-to-caudal and ventral-to-dorsal directions. The two lungs should always be fully auscultated. The absence of sound is a pathological sign. However, sounds may be 83

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bovine respiratory disease

Figure 19. Lesion in the nasal mucosa caused by bovine herpesvirus 1.

Figure 20. How to smell the air exhaled by the animal.

Figure 21. Auscultation of the ventral region of the right lung.

Figure 22. Auscultation of the middle region of the right lung.

Figure 23. Auscultation of the dorsal region of the right lung.

Figure 24. Auscultation of the trachea.

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