What we know (and don’t know) about pneumonia in beef calves prior to weaning

What we know (and don’t know) about pneumonia in beef calves prior to weaning

David R. Smith, DVM, PhD Mississippi State UniversityCollege of Veterinary Medicine

Is pneumonia an emerging disease of pre-weaned beef calves?

Where do emerging diseases come from? System Dynamics• Emergence of a novel agent

• Acquire new virulence factors• Introduction into a new geo-political region

• Emergence of a known, previously controlled, agent• Emergence of a susceptible host (genetic, nutritional …)• Emergence of a production system that favors a

particular pathogenIncreased Awareness• Mitigation of a disease of greater impact• Social interest –everyone’s suddenly talking about it…

Pre-Weaning Pneumonia in

Beef Calves

Pre-Weaning Pneumonia in Beef Calves

Host-pathogen interactions

Population dynamics

Bovine Respiratory Disease• Recent NAHMS surveys confirm that BRD is the leading

cause of mortality in U.S. feedlot cattle, weaned dairy heifers, and nursing beef calves 3 weeks of age or older –all classes of cattle

• BRD deaths alone cost producers over $643 million annually (2010 estimate, USDA NASS)

• Thus BRD has a significant impact on the profitability of cattle operations and on the health and welfare of cattle

Cost of pre-weaning pneumonia 29,000,000 US beef cow inventory24,650,000 85% calves born alive

147,900 0.6% excess death loss due to BRD400 weaned calf lbs

1.90$ price per pound112,404,000$ 760.00$ losses due to excess BRD mortality

1,479,000 6% treated calves36,975,000 25 lbs weaning wt lost from treated calves70,252,500$ losses due to lost weaning wt from BRD22,185,000$ 15.00$ cost to treat a calf for BRD

204,841,500$ Total cost of BRD prior to weaning.

JAVMA, Vol 243, No. 4, August 15, 2013 538-547

Objective—To identify herd-level risk factors for bovine respiratory disease (BRD) in nursing beef calves.Design—Population-based cross-sectional survey.Sample—2,600 US cow-calf producers in 3 Eastern and 3 Plains states.

Results –Bovine respiratory disease had been detected in at least 1 calf in 21% of operations

JAVMA, Vol 243, No. 4, August 15, 2013 538-547

“Detection of BRD in calves was significantly associated with large herd size, detection of BRD in cows, and diarrhea in calves. Calving season length was associated with BRD in calves in Plains states but not Eastern states.

Cumulative incidence of BRD treatment was negatively associated with large herd size and examination of cows to detect pregnancy and positively associated with calving during the winter, introduction of calves from an outside source, offering supplemental feed to calves, and use of an estrous cycle synchronization program for cows.”

AABP Research Summaries, Milwaukee, WI. Sept 19, 2013

A survey of veterinarians in 6 U.S. states regarding their experience with nursing beef calf respiratory diseaseAmelia R. Woolums, Roy D. Berghaus, David R. Smith, Brad J. White, Terry J. Engelken, Max B. Irsik, Darin K. Matlik, A. Lee Jones, Isaiah J. Smith

ResultsRespondents reported that 18% of their cow-calf clients had nursing calf BRD in the previous year, with 5% of their cow-calf clients having 5% or greater incidence, and 14% of their clients having at least one calf die of BRD.

AABP Research Summaries, Milwaukee, WI. Sept 19, 2013

A survey of veterinarians in 6 U.S. states regarding their experience with nursing beef calf respiratory diseaseAmelia R. Woolums, Roy D. Berghaus, David R. Smith, Brad J. White, Terry J. Engelken, Max B. Irsik, Darin K. Matlik, A. Lee Jones, Isaiah J. Smith

ResultsFrom a list of possible risk factors for nursing calf BRD, at least 50% of respondents selected “weather”, “inadequate colostrum consumption”, “introducing new cattle”, “failure to give nursing calves BRD vaccines”, “failure to give cows BRD vaccines”, “calf diarrhea in the herd”, “vitamin/mineral deficiency for cows/calves”, “protein/energy deficiency for cows/calves”, “BVDV PI cattle in the herd”, and “calving cows and/or heifers in confinement” as contributing to nursing calf BRD.

Component causes!

Component causes• Disease is not observed until the sum of

component causes complete a sufficient cause

• The agent may be necessary for disease• The agent alone may not be sufficient to cause

disease

Mannh. hemol.

BVDV

Cold

D

E

BVDV

Dust

X

ZMannh. hemol.

Mannh. hemol.

PI3

Dust

N

O

Sufficient cause 1 Sufficient cause 2 Sufficient cause 3…

• Infection is common but disease is rare • Until something makes the system “unstable” –

then an apparent disease outbreak• Complete a sufficient cause

• Introduce a new risk factor• e.g. Bovine respiratory disease complex• e.g. Salmonella

• Loss of herd immunity• Age (e.g. neonatal calf diarrhea)• Immunosuppression• Remove antigenic challenge (e.g. stop vaccinating)

Disease control programs may create naïve subpopulations –susceptible to outbreaks! eg. BVDV

Component Causes Explain Endemic Stability

Time dependent factors of the production system affect pathogen exposure and the immune response

• Passive immunity

• Age• Pathogen

survival• Pathogen

exposure• Stressors• Nutrition• Parasitism• Pregnancy

Weaning

Surgery

Mud

Heat

Cold

Nutrition, Genetics…

Commingling

Immunity

Exposure

Time

Exposure and immunity as a function of time

BRD in Pre-weaned Calves: When and Why?

Agents

Imm

unity

Active immune response

Passive Acquired

Antibodies from colostrum

Age

Immunity

Passive

Antibodies from colostrum

Age

T1/2 of antibodies from colostrum is 16 daysRoth. 2009. Current Vet Therapy Food Anim Pract

0 30 60 90 120 150 1800%

20%

40%

60%

80%

100%

ImmunityAntibodies from colostrum

Age

T1/2 of antibodies from colostrum is 16 daysRoth. 2009. Current Vet Therapy Food Anim Pract

2048512128

Initial antibody titer

Imm

unity

Active immune response

Age

The immune system is functional, but unprimed, at birth

Prior to 5-8 months of age the immune response is weaker, slower, and easier to overcome.Cortese. 2009. Vet Clin NA, 25(1)221-227

Kirkpatrick JAVMA, Vol 233, No. 1, July 1, 2008

Kirkpatrick et al. JAVMA, Vol 233, No. 1, July 1, 2008Early: 67d, 190d Late: 167d, 190d

Kirkpatrick et al. JAVMA, Vol 233, No. 1, July 1, 2008 Early: 67d, 190d Late: 167d, 190d

Age and immunity to BRD

Incidence of BRD by age• 14 years• Pre-weaning data• 14,792 steer calves• Surviving to

feedlot finish

Smith DR. 2013. Unpublished

Pre-weaning BRDHerd 1

• Age distribution of 87 pneumonia cases from among 296 pre-weaned calves from a Nebraska ranch

• 29% cumulative incidence


• Age distribution of 49 pneumonia cases from among 255 pre-weaned calves from a Nebraska ranch



• Age distribution of 96 summer pneumonia cases from 2,065 calves born over a 4 year period.



• Age distribution of 138 summer pneumonia cases from 630 calves born in 2012


110,412 calves20 years

“…there seem to be two periods of increasing BRD transmission rate (0 to 20, and 70 to 100 d of age)…. Epidemiological studies of these phases may lead to management alternatives to decrease BRD incidence.”Snowder et al. 2005. J Anim Sci


“The greater incidence between 75 and 170 d of age may be partially attributed to increased commingling of animals during the breeding season when cows were frequently gathered for AI.”Snowder et al. 2005. J Anim Sci


Herd immunity

• Transmission is hindered because a majority of animals are immune –inefficient transmission means the pathogen may “die out” (R0 <1) before everyone is exposed

• Results in protection of susceptible animals within the group• Better to be the susceptible calf within a pen of

well-immunized cattle, than the only one vaccinated

• For this reason successful vaccine programs are “group-based”

BRSV SN titers179 calves serially sampled

As calves in the population age the distribution of titers shifts to the left

Leaving a smaller proportion of calves protected and a larger proportion of calves susceptible

Data provide by A Woolums

Epidemic CurveHerd 1

• Epidemic curve of BRD in Herd 1.

• Lines represent the proportion of calves at least 100 or 120 days of age each week.


• Epidemic curve of BRD in Herd 2.

• Lines represent the proportion of calves at least 100 or 120 days of age each week.


• Epidemic curve of BRD in Herd 4. • Lines represent the proportion of

calves at least 100 or 120 days of age each week.

Age and immunity to BRD

Incidence of BRD by age• 14 years• Pre-weaning data• 14,792 steer calves• Surviving to

feedlot finish


Age and BRD by year

Mean days of age at BRD treatment = 89.4Median = 91.4

• 14 years• Pre-weaning data• 14,792 steer calves• Surviving to feedlot

finish• Error bars = 1 stdev


BRD by year• 14 years• Pre-weaning data• 14,792 steer calves• Surviving to feedlot

finish• Significant

differences by year in BRD cumulative incidence


Ranch vs Feedlot BRD

Incidence of BRD on the ranch appeared unrelated to incidence of feedlot BRD


Line of equivalence

Ranch incidence greater

Feedlot incidence greater

Ranch vs Feedlot BRD

Some years calves with BRD on the ranch were at greater risk for BRD in the feedlot, some years it was the opposite.


Calf gender is associated with BRD risk

5,078 calf records from 4 ranches and 20 management groups.

Adjusting for age of the dam, heifer calves were less likely (OR = 0.83) and bull calves more likely (OR = 1.46) than steers to develop BRD prior to weaning (p=0.01)

Age of the dam is associated with BRD risk

5,078 calf records from 4 ranches and 20 management groups. Adjusting for gender, compared to calves born to cows 4 years or older, calves with two year old dams and 3 year old dams had 1.67 and 1.11 times greater odds for BRD (p=0.0004)

Conclusions from ranch BRD outbreak investigations

Calf level characteristics:• Age of the dam affects BRD risk• Gender of the calf may affect BRD risk

Herd level characteristics:• Two patterns of occurrence of pneumonia

• sporadically in young calves • large sudden outbreaks in older calves


The explanation of these two patterns may be:

• failure of passive transfer resulting in more sporadic cases in very young calves

• Loss of herd immunity resulting in outbreaks of pneumonia in older calves.


• Herd immunity (or lack of it) may play an important role in the occurrence of pneumonia in ranch calves.• Increased incidence of BRD in calves ~90-150 days of age• Sudden outbreaks of BRD when a large portion of the herd is in this age

range• Lose endemic stability• Susceptible = potentially infective resulting in overwhelming exposure

• Other time related environmental/management factors may affect pathogen exposure and host susceptibility

Acknowledgements• Amelia Woolums, UGA• Dale Grotelueschen, UNL GPVEC• Suzanne Genova, MSU• Russ Daly, SDSU• Gerald Stokka, NDSU• Al Doster, Dustin Loy, Bruce Brodersen UNL VDC• Many ranchers and veterinarians throughout the US

A contribution of the Beef Cattle Population Health Program at Mississippi State University. Supported by the Mikell and Mary Cheek Hall Davis Endowment for Beef Cattle Health and Reproduction.Supported in part by a grant from Zoetis

David R. Smith, DVM, PhD

Dipl. ACVPM (Epidemiology)

Mikell and Mary Cheek Hall Davis Endowed Professor

Beef Program Leader

[email protected]

Dept. of Pathobiology and Population Medicine

PO Box 6100, 240 Wise Center Drive, Rm A1204

Mississippi State, MS 39762

What we know (and don’t know) about pneumonia in beef calves prior to weaning

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