Bovine Respiratory Disease Overview

Bovine Respiratory Disease (BRD)

• BRD is a significant disease complex affecting cattle, with varied presentations.
• Learning objectives include describing classifications, identifying infectious agents (viral and bacterial), and discussing risk factors, clinical signs, and treatments for various forms of BRD in different cattle groups (nursing dairy calves, stockers, feedlots).

Bronchopneumonia (BP)

• BP is characterized by the invasion of pathogenic organisms into the lungs through the bronchial tree.
• Clinical signs of BP typically involve fever, depression, and indications of sepsis.

Bronchointerstitial Pneumonia (BIP)

• BIP is a complication of bronchopneumonia, characterized by interstitial lung disease.

Metastatic Pneumonia

• This form of pneumonia results from septic embolisms originating from other body locations.
• Rumen acidosis and liver abscessation are associated sequelae.
• Cattle rations high in rapidly fermentable carbohydrates trigger rumen acidosis and rumenitis. This leads to liver abscessation, and thrombosis of the vena cava.
• Septic thrombi form and spread, potentially impacting the caudal vena cava.

Interstitial Pneumonia (AIP)

• AIP results from an interstitial reaction, potentially caused by ingestion or inhalation of toxins or allergens, or viral respiratory tract infections.
• It is characterized by bilateral lung infiltrates and diffuse alveolar damage.
• Viral infection (BRSV, naïve or immunocompromised animals) and feedborne pneumotoxins (3-Methyl Indole, "Fog fever", Perilla Mint ketone, 4-ipomeanol (moldy sweet potato)) are known causes.

Bovine Respiratory Disease: Bronchopneumonia

• Viral infection of the upper respiratory tract (URT) often precedes bacterial colonization of the lungs in bronchopneumonia.
• This leads to increased bacterial numbers, prolonged shedding periods, and more severe disease outcomes.

Viral-Bacterial Synergy

• Viral infections affect the mucocilliary apparatus and immune cell function (macrophages) in cattle.
• This results in altered mucus, decreased mucociliary velocity, impaired immune responses, and tissue damage.
• Bacterial colonization further impacts the immune response in compromised animals via the altered TLR pathways—increasing neutrophil death and dysfunction.

Bovine Respiratory Disease Complex: Bronchopneumonia

• Viruses associated with BRD include Bovine Herpes Virus-1 (BHV-1), Bovine Respiratory Syncytial Virus (BRSV), Bovine Viral Diarrhea Virus (BVDV), Parainfluenza 3 Virus (P13), Coronavirus, and Influenza D.
• Bacterial pathogens include Mannheimia haemolytica, Pasturella multocida, Histophilus somni, and Mycoplasma bovis.

BRDC Bronchopneumonia - Clinical Signs

• Clinical signs of BRD bronchopneumonia show little variation between pathogens.
• Typical signs include fever, cough, anorexia, depression, increased respiratory rate, and reduced milk production

BRDC - Primarily in Calves

• Dairy calves are affected mostly before the age of 3 months.
• Beef calves are affected during the preweaning and post-weaning phases (under five months and 5 to 8 months respectively).

Nursing Dairy Calves

• Incidence data (1991–2007) illustrate that respiratory diseases are a significant source of calf mortality in both pre-weaned and weaned calves, encompassing percentages of 8.4–10.8% and 2.2–2.8% respectively.

Pathogens Associated With Nursing Dairy Calf Disease

• Data shows Mycoplasma bovis is a significant pathogen in nursing dairy calves, comprising 50% of total isolates.

Measures to Reduce BRD Risk in Nursing Dairy Calves

• Feeding only waste or saleable milk (transition milk) while providing more than 4 liters of milk per day to calves less than 21 days old.
• Vaccinating dry cows prior to calving.

Stocker/Feedlot Cattle

• Factors triggering BRD in this group include weaning, comingling, transportation, new environments, compromised host immune function, and nutrition.

Common Causes of Morbidity in Stockers/Feedlots

• This section compiles data on morbidity and mortality rates associated with various cattle conditions and feedlot capacities.

Stocker/Feedlot Multifactorial Disease Syndrome

• Preweaning factors, including prenatal nutrition, colostrum intake and BVD persistence also influence immune function.
• Postweaning factors, including receiving period management, stress, and nutrition also affect cattle susceptibility.

Stocker/Feedlot Risk Factors

• Arrival weight of the cohort is a risk factor. Lower weight correlates to a higher risk of morbidity and mortality.
• Gender (bulls) shows a greater risk of morbidity and mortality compared to heifers.
• Arrival month (September-November) is a factor linked to increased risks

Feedlot Cattle Prep Conditioning

• Procedures include castration and deworming; weaning at least 45 days before shipping; training to eat from a feed bunk and drink from a water trough.

Stocker/Feedlot Importance of Preconditioning

• Preconditioning positively affects average daily gain (ADG), morbidity rates, treatment requirements, chronic disease frequency, and medical costs.

Mannheimia haemolytica Highlight

• Mannheimia haemolytica is a Gram-negative, facultative anaerobic rod.
• Various serotypes exist, with some being pathogenic and others nonpathogenic commensals.
• Serotype A1 and A6 are commonly implicated in BRD cases, while serotype A2 is more frequently found in healthy cattle.

Mannheimia haemolytica: Lipopolysaccharide

• A systemic inflammatory response syndrome (SIRS) response is noted upon infection.
• Clinical signs include tachycardia, tachypnea, cool extremities, and dark mucous membranes.

Mannheimia haemolytica: Leukotoxin

• Leukotoxin is an essential virulence factor.
• It binds to cells via CD18, causing the death of bovine leukocytes.
• This factor leads to neutrophil lysis and the release of digestive enzymes.

Metastatic Pneumonia: Two Presentations

• Chronic weight loss and intermittent fever, coupled with coughing are common symptoms.
• Second presentation involves hemoptysis, epistaxis, tachycardia, tachypnea, and coughing accompanied by heart murmurs.

Metastatic Pneumonia: Clinical Findings

• Clinical signs of pneumonia can include bloody discharges or abnormal heart sounds.

Metastatic Pneumonia: Ultrasound

• Findings could include dilated caudal vena cava.

Metastatic Pneumonia Treatment

• Prognosis is typically poor; treatment mostly focuses on supportive care.
• Antimicrobials target specific bacteria (e.g., T. pyogenes, F. necrophorum, E. coli)
• Nutritional and management changes address acidosis as the condition's root cause.

Necrotic Laryngitis

• This is an infection of laryngeal mucosa and cartilage.
• Acute or chronic laryngeal contact ulcers are essential for illness progression.
• Invasive respiratory commensals often cause the condition, with Fusobacterium necrophorum being a major contributor.

Necrotic Laryngitis: Clinical Signs

• Calves between 3 – 18 months of age are affected by overcrowded or feedlot conditions.
• Clinical signs involve increased respiratory distress, moist, painful cough, inspiratory dyspnea with stertor and an extended head/neck posture and ptyalism (drooling).

Necrotic Laryngitis: Diagnosis

• Usually, diagnosis relies on clinical signs.
• Endoscopy and radiographic methods also aid in the diagnosis.
• Ultrasound can support diagnosis.

Necrotic Laryngitis: Treatment

• Antimicrobials—Florfenicol (20 mg/kg IM q48 hr or 40 mg/kg SQ once).
• Corticosteroids —Dexamethasone (0.1 mg/kg IV/IM for 2-3 days).

Interstitial Pneumonias

• Interstitial pneumonia is an idiopathic form of acute lung injury characterized by bilateral lung infiltrates and diffuse alveolar damage.

Interstitial Pneumonia (ARDS):

• Acute Respiratory Distress Syndrome (ARDS) is noted as acute progressive dyspnea and tachypnea with hypoxemia.

Interstitial Pneumonias: Known Causes

• Viral Infection (BRSV naïve or immunocompromised animals).
• Feedborne pneumotoxins (e.g., 3-Methyl Indole, "Fog fever", Perilla Mint ketone, 4-ipomeanol (moldy sweet potato)).

Interstitial Pneumonia: Fog Fever

• Primarily affecting adult cattle over 2 years of age, the condition is linked to the change in grazing patterns from sparse winter forage to lush spring pastures triggering the conversion and production of 3-methylindole.

Interstitial Pneumonia: Fog Fever: Clinical Signs

• The onset is typically noticed within two weeks of changing pastures.
• Clinical signs consist of sudden dyspnea with a loud expiratory grunt, frothing/accumulation of secretions in the mouth, open-mouthed breathing and rapid breathing rate.

Interstitial Pneumonia: Treatment

• Specific treatment for interstitial pneumonia is lacking.
• Prognosis for treatment varies according to the condition extent.
• Affected animals may be moved to calmer pastures, supportive care, and if possible, diuretics and corticosteroids may be considered.