Ruminant Resp Disease Epidemiology and Economics

Bovine Respiratory Disease Complex (BRDC)

Clinical syndrome of undifferentiated fever with respiratory signs, not a single causal agent

Multifactorial BRD triad

Disease requires the convergence of host susceptibility, pathogen exposure, and environmental stress

What are the components of shipping fever?

Occurs in recently transported/received feedlot calves, days to a month after arrival

Acute fibrinonecrotic pleuropneumonia

Classically Mannheimia haemolytica

What are the components of enzootic pneumonia?

In pre-weaned dairy and veal calves

Endemic bronchopneumonia

Viral initiation with bacterial and mycoplasma involvement

What are the components of acute interstitial pneumonia?

In late feeding period feedlot cattle

Distinct syndrome that is not classic BRD, it has a separate pathogenesis

What constitutes subclinical BRD?

Ultrasound screened calves of any sector

Lung consolidation without detectable clinical signs

Aerogenous bacterial bronchopneumonia distribution

Cranioventral distribution

Acute interstitial pneumonia distribution

Diffuse caudodorsal distribution

Bovine lung collateral ventilation

Poor collateral ventilation due to complete lobular septa

What is a key purchasing consideration for feedlot clients when it comes to BRD risk?

Lighter weight cattle at placement carry a substantially higher risk

How does the cow-calf sector compare to the feedlot?

Lower incidence than the feedlot but still a leading cause of death

This sector determines feedlot risk

WHERE PREVENTION LEVERAGE IS GREATEST

Why do cattle who have "recovered" from BRD never truly recover?

Alveolar architecture does not regenerate - heals by fibrosis

Exudate causes fixed obstruction and affected lobules remain atelectic

Reduced aerobic capacity for metabolic demands

When does BRD occur?

At transport and weaning

Peak BRD risk period in feedlots

Within the first 7 to 27 days after arrival

How does later onset BRD compare to the early onset (those that occur shortly after feedlot arrival)

Has different risk factors and worse outcomes

Overlaps with acute interstitial pneumonia

When should we vaccinate to prevent BRD?

2-3 weeks before the stressful event

What risk factor does the producer have the most control over in relation to BRD?

Weaning, which is the first major stressor for calves

Why does weaning increase BRD risk?

Abrupt maternal separation produce stress

Dietary transition reduces intake when energy demands rise

Loss of maternal Abs

Cortisol elevation impairs immune system

Frequently bundled with castration, dehorning, transport

Is BRD heritable?

Is it a very low heritability but yes

BRD has the highest incidence around what time of year?

Fall

What are the 2 distinct risk windows for dairy cattle to get BRD?

Pre weaned calf (0-8 weeks)

Weaned heifer

Characteristics of BRD in pre-weaned dairy calves

Morbidity incidence peaks in weeks 3-6 of life

Frequently subclinical

Dominant risk factors for pre-weaned dairy calves obtaining BRD

Serum IgG concentration (passive transfer)

Birth weight

Ventilation type

Temperature humidity index

Consequences of BRD in pre-weaned dairy calves

Reduced ADG

Reduced first lactation yield

Altered reproductive performance

Risks for BRD in weaned heifers

Stocking density

Ventilation

Air quality

Pen mixing and regrouping

Why are weaned heifers prone to BRD?

Timing coincides with loss of maternal antibodies and grouping of previously individually housed calves

What is the most modifiable risk factor for BRD in the pre-weaned dairy calf?

Transfer of passive immunity

Excellent passive transfer threshold (serum IgG)

≥15.0 mg/dL (serum total protein ≥5.4 g/dL)

Failure of passive transfer threshold (serum IgG)

Herd level target for passive transfer

At least 90% of calves should exceed the excellent transfer threshold

Why are additional treatments so detrimental to economic loss?

The relationship is non linear, the economic penalty of a second treatment is much larger than the first