Bovine Respiratory Disease

Question 1

describe bovine respiratory disease: bronchopneumonia

Answer 1

1. opportunistic disease
2. invasion of pathogenic organisms into lung through bronchial tree
3. characterized by fever, depression, signs of sepsis
4. viral infection of URT precedes bacterial colonization of lung
   -increased bacterial numbers
   -longer duration of shedding
   -increased disease severity

Question 2

describe the viral-bacterial synergy of bovine respiratory disease

Answer 2

1. viral infections affects:
   -mucous
   -mucociliary apparatus
   -immune cell function: reduced macrophage functions, tissue damage secondary to neutrophils
2. viruses: ON EXAM
   -bovine-herpes virus-1 (BHV-1)
   -bovine respiratory syncitial virus (BRSV)
   -bovine viral diarrheal virus (BVDV)
   -parainfluenza 3 virus (PI3)
   -coronavirus
   -influenza D
3. bacteria: ON EXAM
   -mannhemia hemolytica
   -pasturella multicoda
   -histophilus somni
   -mycoplasma bovis

Question 3

describe BRDC bronchopneuomonia clinical signs

Answer 3

little variation between pathogens

1. fever
2. cough
3. anorexia
4. depression
5. increased respiratory rate/effort
6. reduced milk production

Question 4

who is primarily affected by BRDC?

Answer 4

calves!!

dairy: <3 months of age
-big contributor to pre-weaned and weaned calf mortality!!

beef:
-preweaning: <5 months, 1st round of cases seen
-post weaning: 5-8 months, 2nd round of cases seen

Question 5

describe measures to reduce BRD in nursing dairy calves

Answer 5

1. feeding only waste or saleable milk (transition milk)
2. feed >4L of milk per day in calves <21 days of age
3. administration of vaccines to dry cows prior to calving (boost colostral antibody protection)

Question 6

how does BRD emerge in beef cattle?

Answer 6

transfer to feedlot, weaning, new pathogen exposure, comingling, change in diet, and stress cause a disequilibrium of pathogens

shipping fever/BRD is a HUGE cause of morbidity in beef

a multifactorial disease/syndrome with preweaning, postweaning, and feedlot factors

Question 7

describe risk factors for BRD in stocker/feedlot

Answer 7

1. arrival weight of cohort:
   -lower weight = greater risk: 20-35% increase in mortality risk for each hundred weight decrease
2. gender:
   -bulls= greater risk in both morbidity and mortality
3. month of arrival:
   -september-november (colder months = harder to thrive)

Question 8

describe preconditioning of feedlot cattle (4)

Answer 8

1. castrate
2. vaccinate/deworm
3. wean at least 45 days prior to shipping
4. train to eat from a feed bunk and drink from a water trough

all require producers to spend money so may see resistance but convince them of the benefits! (increased average daily gain, decreased morbidity, decreased medical costs once enter feedlot)

Question 9

describe mannheimia hemolytica

Answer 9

1. gram negative facultative anaerobic rod
2. 12 serotypes
   -some pathogenic, others nonpathogenic commensals
   -serotypes A1 and A6 = most common isolated from BRD cases
   -serotype A2: most common serotype in normal cattle
3. lipopolysaccharide
   -causes SIRS, resulting in tachycardia, tachypnea, cool extremities, and dark mucous membranes
4. leukotoxin: essential virulence factor
   -binds to cells via VD18
   -causes death of bovine leukocytes
   -neutrophil lysis and release of digestive enzymes, causes lysis and death of other cells = so much dead lung tissue on necropsy (fibrin coating)

Question 10

describe bronchopneuomia treatment

Answer 10

1. gold standard: antimicrobials
   -tulathromycin, enrofloxacin, danofloxacin, florfenicol commonly used
2. parenteral; 16 compounds registered for use
   -lots of resistance developing as we use them but little evidence to support any other modality

Question 11

describe vaccination against BRD

Answer 11

1. numerous multivalent vx
   -modified live or killed
   -parenteral or intranasal
2. differences in efficacy
   -dairy versus beef
   -weaned versus preweaning

Question 12

describe metastatic pneumonia

Answer 12

1. septic embolization of lungs from other foci in the body
   -sequelae to rumen acidosis and liver abscessation
2. cattle feed rations are high in rapidly fermentable carbohydrates
   -rumen acidosis
   -rumenitis
3. leads to liver abscessation
4. leads to thrombosis of vena cava
   -spread of emboli from septic thrombi in caudal vena cava

Question 13

describe the 2 presentations of metastatic pneumonia

Answer 13

1. chronic weight loss and coughing, intermittent fever
2. hemoptysis and epistaxis
   -tachycardia, tachypnea, coughing, heart murmurs

diagnostic clue: dilated caudal vena cava

Question 14

describe treatment and prognosis of metastatic pneumonia

Answer 14

1. prognosis is poor:
   -therapeutics generally unrewarding
   -antimicrobials and other supportive care: T. pyogenes, F. necrophorum, E. coli
   -gram negative, anaerobia spectrum
2. control conditions that precipitate disease
   -nutritional management to reduce occurrence of acidosis

Question 15

describe necrotic layngitis

Answer 15

1. infection of laryngeal mucosa and cartilage
   -acute or chronic
2. laryngeal contact ulcers essential to development of disease
   -invasion of tissue by respiratory commensals: fusobacterium necrophorum!
3. clinical signs:
   -calves: 3-18 months of age
   -feedlots or overcrowded conditions
   -moist painful cough
   -inspiratory dyspnea with stertor: head and neck extended
   -ptyalism/hypersalivation
4. diagnosis:
   -clinical signs usually sufficient
   -endoscopy or radiographs (rarely done)
   -ultrasound
5. treatment:
   -antimicrobials: florfenicol
   -corticosteroids: dexamethasone
   -tracheostomy: allows airway to rest, which accelerates healing, and allows them to breathe enough to eat

Question 16

describe interstitial pneumonias

Answer 16

1. interstitial reaction to ingestion or inhalation of toxins or allergens
   -viral respiratory tract infection
2. idiopathic form of acute lung injury characterized by:
   -bilateral lung infiltrates
   -diffuse alveolar damage
3. pathologic definition confirmed by microscopic analysis of lung tissue from animal with characteristic history and clinical signs

Question 17

describe acute respiratory distress syndrome as relates to interstitial pneumonia

Answer 17

1. acute onset of progressive dyspnea, tachypnea, and hypoxemia
2. pulmonary/extrapulmonary insult causes release of inflammatory mediators
   -neutrophil accumulation
   -pulmonary edema, hyaline membrane formation
   -decreased lung compliance

Question 18

describe known causes of interstitial pneumonia

Answer 18

1. viral infection: BRSV; naive or immunocompromised animals
2. feedborne pneumotoxins:
   - 3-methyl indole/fog fever
   -perilla mint ketone
   - 4-ipomeanol (moldy sweet potato)

Question 19

describe interstitial pneumonia fog fever

Answer 19

1. adult cattle: >2 years of age
2. associated with ration changes
   -dry, sparse winter forage to lush green pastures in spring
   -conversion of L-tryptophan to 3-methylindole (3MI) by rumen microbes (rest is FYI of pathogenesis)
   -3MI is metabolized by cytochrome P450 enzymes in clara cells and type I alveolar epithelial cells
   -production of more toxic metabolites that bind cellular macromolecules
   -damage and death of clara cells, type I cells, endothelial cells
   -leakage of proteinaceous fluid into alveoli (hyaline membranes) cause emphysema, edema, and hemorrhage
   -proliferation of type II alveolar epithelial cells, micxd inflammatory cell infiltrate
3. within 2 weeks of pasture change to lush pasture:
   -acute onset of dyspnea with loud expiratory grunt
   -frothing at mouth
   -mouth breathing
   -tachypnea
4. treatment:
   -none specific
   -careful removing from offending pastures
   -if attempted: diuretics, corticosteroids