Lecture 15: Introduction to Bovine Respiratory Disease

BRD

• leading health problem in feedlots worldwide

• most costly cattle disease

• major driver of antimicrobial use in beef industry

what is BRD?

• multifactorial syndrome

• shipping fever, enzootic pneumonia, BRDC

• syndromic diagnosis rather than single disease

perfect storm model

• stressors → weaning, castration.dehorning, transport, diet change

• pathogen exposure

• host immunity → naive calves, poor colostrum transfer, vaccine gaps

• environmental triggers → cold snaps, dust, mud, heat stress

who is at risk for BRD?

• pre-weaned dairy calves

• weaned/backgrounded beef calves

• auction sourced vs ranch direct calves

• feedlot cattle

what is preconditioning?

• weaning 30-45 days before marketing

• vaccination prior to sale

• castration and dehorning performed and healed pre-transport

• bunk and water training to reduce post-arrival stress

economics of preconditioning

• lowers treatment and death rates

• improved average daily gain and feed efficiency

• may command premiums at sale barns

• costs → feed, labor, facilities at cow-calf level

• profitability = margin between added costs and health gains

feedlot animals

• cattle commingled from multiple sources

• exposed to new pathogens on arrival

• high risk groups = lightweight, long-haul, auction commingled

• low risk groups = ranch-direct, heavier weight, preconditioned

• BRD incidence peaks in first 45 days on feed

BRD host factors

• young calves have immature immunity

• passive transfer status → colostrum critical

• genetic differences in disease susceptibility

• pre-existing disease or chronic stress load

• vaccine history

BRD environment factors

• dust, ammonia, and poor air quality impair defenses

• weather extremes

• mud and poor pen conditions increase stress and energy

• poor ventilation and high stocking density

• seasonal clustering

when are peak BRD outbreaks?

fall

BRD management factors

• transport distance, shrink, rough handling

• auction commingling increases exposure

• stressful arrival processing

• sudden ration changes or poor bunk management

• timing and quality of preventative measures

pathogen risks of BRD

• viruses → impair cilia

• bacteria

• pathogens act synergistically with stress/environment

right bovine lung

cranial, middle, caudal, accessory lobes

bovine left lung

cranial and caudal

tracheal bronchus in bovine supplies

right cranial lobe

which lung is bigger in bovine?

right

borders of lungs in adult cows

• cranial → 1st rib→3rd ICS

• caudal → 11th rib mid-thorax → 9th rib at midline → olecranon

• dorsal → transverse processes

early recognition of BRD

• off-feed, standing apart from pen mates

• droopy ears, dull eyes, rough coat

• reluctance to move, lagging behind herd

• increased lying behavior

• ADR

BRD PE

• temp → fever

• increased RR

• nostril flare, abdominal push, open-mouth breathing

• nasal discharge: serous = viral, mucopurulent = bacterial

• ocular discharge → IBR conjunctivitis vs bacterial pus

• cough quality → moist vs harsh hacking

• dehydration, poor rumen fill, weight loss

examining thorax for BRD

• auscultation in quiet setting preferred

• compare side to side, ventral to dorsal, cranial to caudal

• note both adventitious and absent sounds

• assess symmetry of findings

cranioventral findings on lungs

• crackles and bronchial sounds over CV fields

• harsh inspiratory sounds = consolidation

• dull or absent sounds = severe consolidation or pleural effusion

• lesions concentrate here due to gravity and airway deposition

• classic site for bacterial pneumonia

caudodorsal findings on lungs

• harsh, coarse sounds with expiratory grunts

• diffuse wheezes

• quiet dorsals with severe dyspnea → interstitial edema/emphysema

• acute open-mouth breathing and froth = hallmark of AIP

• common in finishing cattle

bronchopneumonia pathology

CV consolidation, fibrin, suppuration

acute interstitial pneumonia pathology

CD emphysema/edema, interstitial thickening

when lung sounds mislead

• thick chest wall muffles crackles/wheezes

• ambient pen noise can obscure subtle sounds

• subclinical pneumonia often silent

• chronic fibrosis can be silent despite pathology

• always integrate PE with herd history and risk profile

clinical scoring systems

• DART = depression, appetite, respiration, temp

• wisconsin calf resp score

• improves consistency across staff and research projects

• early pull decisions = better outcomes

thoracic ultrasound basics

• detects subpleural consolidation and pleural fluid

• more sensitive than auscultation for parenchymal disease

advanced ultrasound use

• useful in dairy calf operations for early intervention

• less practical in large feedlots

sampling the lower airway

• deep nasal swab → easy but contamination risk

• guarded tracheal wash → better for lower airway pathogens

• BAL

• PCR panels

preconditioning programs

• premiums possible at auction, variable by region

• cost

• payoff

• long-term benefits in welfare and consumer perception

risk triage at arrival

• high risk → auction calves, lightweight, mixed origin, unvaccinated

• medium risk → ranch-direct but no preconditioning

• low-risk → preconditioned, heavier weight, uniform source

vaccination timing

• prefer ranch-based vaccination

• arrival vaccination

• booster timing important

metaphylaxis

• antimicrobial given to group on arrival

• best for high risk cohorts

• improves ADG, reduces death loss

• avoid blanket use in low risk cattle

husbandry and environment

• stocking density → avoid overcrowding

• ventilation

• dust and ammonia control

• bunk management

• water access, clean troughs essential

• nutrition