29-30. bovine respiratory disease I & II

consequences of dairy calf pneumonia

associated with

• death

• poor growth

• dystocia

• poor adult performance

classic clinical signs associated with BRD

• fever

• depression

• inappetence

• ocular / nasal discharge

• cough → most reliable indicator of pneumonia, but cannot r/o pneumonia if absent

• droopy ears

• dyspnea

**note: subclinical disease exists; severity of lung disease is NOT well correlated to severity of clinical signs

bronchopneumonia — gross & histologic lesions

• gross lesions: cranioventral consolidation (firm to hard)

• histologic lesions: neutrophils & fibrin fill alveoli & bronchioles

  • neutrophilic infiltrate into the airways

  • respiratory epithelium typically unaffected (unlike viral/toxic disease)

bronchopneumonia — commonly isolated bacteria(-like) pathogens

pasteurella multocida ≥ mycoplasma (mycoplasmopsis) bovis > mannheimia hemolytica

bronchopneumonia — less commonly isolated bacteria

• histophilus somnus (also pleuritis)

• bibersteinia trehalosi

• trueperella pyogenes

what type of pneumonia does salmonella dublin cause?

interstitial pneumonia, not bronchopneumonia

• significant problem in SOME herds

what finding is pathognomonic for M. bovis?

caseous necrosis (but not always present)

common causative agents of viral pneumonia (airway disease / injury)

• BRSV

• BHV-1

• PI₃

• BVDV — impairs host resistance

• possibly: coronavirus (adenovirus, bovine rhinovirus)

pathophysiology / pathologic findings of viral airway disease

• respiratory epithelial injury

  • inflammation & necrosis of bronchiolar epithelium

• infiltrates around airway

• obstruction of airway with debris & atelectasis

• bronchoconstriction

• does not result in consolidation associated with bronchopneumonia

lesion associated with BHV-1 (infectious bovine rhinotracheitis)

erosions / ulcerations in trachea

• r/o expectorated exudate from lung → easily wiped off with a finger, whereas IBR lesion is ulcerated and cannot be removed

BRD risk factors

• failure of passive transfer

• commingling

• concurrent disease

• poor ventilation

• extended transport time

• exposure to wet / cold or wide temp swings

• stressful processing procedures

• recent weaning

• poor vaccination history

• nutritional problems / deficiencies

  • copper, selenium, zinc, manganese, iron, vitamin A & E particularly important due to their involvement with the immune system

BRD protective factors

• supervised calvings

• IgG >800 g/dL

• individual housing

• solid barriers between individual calf pens

• bedding deep enough to cover legs (nesting)

• decreased total bacterial counts in pen air

negative prognostic indicators

• distress in the face of multiple previous treatments

• small stature or poor body condition

• lung abscesses / necrosis

• caudal lung lobe involvement

**discuss euthanasia!

signs of distress

• persistent open mouth breathing

• stretched head and neck

• labored breathing

• prolonged inappetence or recumbency

must discuss and encourage euthanasia; supportive care (NSAIDs, fluids) to make comfortable while deciding

what should be done with chronically ill but not distressed animals?

monitor closely for QOL; separate from group to minimize competition; cull once drug withdrawal periods have elapse

what methods of diagnosing BRD have low sensitivity or are unreliable?

• producer diagnosis (56% sensitivity)

  • gold standard: necropsy

• stethoscope (6% sensitivity)

  • gold standard: ultrasound lesions

• unreliable

  • rectal temperature

  • respiratory rate

  • WBC counts

what strategy should producers use to find acutely sick calves?

check for acute, severe disease 2x/day

• off feed

• abnormal behavior

• constant cough

• copious nasal discharge

• depression

how should producers define respiratory disease for sick individual calves?

2 or more of the following:

• fever (T: ≥ 103°F)

• moderate nasal discharge

• multiple inducible coughs

  • or spontaneous

• moderate ocular discharge

• droopy ear(s)

diagnostic strategies for BRD

• identify agent

• test affected but untreated calves

• culture & sensitivity

  • nasal swabs

    • only useful to identify susceptibility patterns

  • deep nasal pharyngeal swabs (sample from back of throat)

    • help identify causative organism

    • test 6 animals (2 swabs per calf)

  • trans-tracheal fluid

  • BAL fluid

  • lung tissue samples

• molecular methods

  • PCR on swabs/fluid

    • complete bovine respiratory panel — PCR for bacterial & viral pathogens, bacterial C&S

what family of antibiotics accumulate within the lung tissue?

macrolides

which class of antibiotics is not effective for mycoplasma (M. bovis or dispar)?

beta-lactams