Bovine respiratory disease (BRD), also known as shipping fever or pneumonia, is a significant problem for dairy replacement heifers. According to reports from the National Animal Health Monitoring System (NAHMS), 18.1% of pre-weaned dairy heifers experienced respiratory disease (USDA 2012), but respiratory problems accounted for 22.5% of deaths in unweaned heifers and 46.5% in weaned heifers (USDA 2010). That means respiratory disease is the single greatest cause of heifer deaths after weaning. Long term effects on performance include decreased probability of survival to first calving, decreased growth, delayed age at first calving, increased probability of having a difficult delivery at first calving, premature culling, and reduced lifetime profit (Heinrichs et al 2005, Guliksen et al 2009, Stanton et al 2012, Bach 2011).
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Early detection and treatment of sick animals is important regardless of cause. Often there are multiple causes such as a combination of viral and bacterial infections along with various management and environmental stressors. Among a group of animals, individuals may be observed with varying severity and stage of disease. Diagnostic tests can be expensive, so care takers should be trained to consistently assess an animal’s health status. BRD scoring systems present a way to standardize diagnosis across a large number of animals.
Simple and Useful Tool to Assess Respiratory Disease
The usefulness of a disease scoring system for dairy farms is limited by the logistics and practicalities of on-site implementation. A new on-farm bovine respiratory disease (BRD) scoring system has recently been created in an effort to provide an easy and accurate way to diagnose BRD in pre-weaned dairy calves (Love et al. 2014).
Five’s the Limit
This simplified scoring system assesses six clinical signs. When present, a specific number of points are assigned for each sign. A total score of 5 or higher classifies an individual as a BRD case.
- Cough = 2 points
- Eye discharge = 2 points
- Fever (> 39.2oC) = 2 points
- Abnormal respiration = 2 points
- Nasal discharge = 4 points
- Ear droop or head tilt = 5 points
One of the advantages of this system is that a rectal temperature is not needed for every calf; it is only needed if the total score for the visible signs is 4. A temperature could then tip the score over the cutoff of 5.
Please see Figure 1 for a detailed outline of the scoring. A printable version of the scoring system (in English and Spanish) can be found at: http://www.vmtrc.ucdavis.edu/laboratories/epilab/scoringsystem.pdf.
Figure 1. Scoring matrix for the simplified scoring system. (http://www.vmtrc.ucdavis.edu/laboratories/epilab/scoringsystem.pdf)
Simple and Accurate
Validation of the simplified scoring system was performed by scoring 500 hutch-raised calves in parallel on both the new system and the Wisconsin system. The Wisconsin system uses five clinical signs scored by level of severity (http://www.vetmed.wisc.edu/dms/fapm/fapmtools/8calf/calf_respiratory_scoring_chart.pdf). In addition to scoring with both systems, the calves were evaluated for pneumonia using a stethoscope and ultrasound of the lungs. Sensitivity and specificity were determined for each system (Table 1) (Aly et al. 2014). Sensitivity is a measure of the proportion of true positives among all of the positive results (i.e., the number of actually diseased animals, as determined by clinical signs in combination with microbiological testing and abnormal lung sounds or abnormal ultrasound, which return a positive test result – the rest are false positives). Specificity measures the opposite, the proportion of true negatives among all of the negative results (i.e., the number of healthy animals that return a negative test result – the rest are false negatives).
Table 1. Sensitivity and specificity of each scoring system performed on the same 500 calves.
|
System |
Sensitivity |
Specificity |
|
Simplified system |
72.3% |
89.9% |
|
Wisconsin system |
70.8% |
93.1% |
*The difference in sensitivity is not statistically significant (P=0.695). The difference in
specificity is statistically significant (P=0.041), but the implications of this are currently unknown.
Table 1 shows that both systems result in comparable sensitivity and specificity.
Further research on the diagnostic performance of BRD scoring systems in entire populations, as well as the development of a customizable risk assessment tool, are underway.
Benefits of Respiratory Scoring
At the end of the day, the best scoring system for a particular farm is the one that will actually be used on a regular basis to determine which animals are sick. A simplified system that is easy to implement allows for the identification of sick animals more efficiently, thereby allowing them to be treated in a timelier manner. This has positive implications not only for the individual calf, but overall for animal welfare improvement.
To view a presentation about the simplified scoring system, please visit: https://www.youtube.com/watch?v=4r0CQOZ1s9Y.
To view a presentation about the Wisconsin system, please visit: https://www.youtube.com/watch?v=uGOCn2NcAOo.
Author Information
Amy Young
Staff Research Associate, UC Davis
References
Bach A. 2011. Associations between several aspects of heifer development and dairy cow survivability to second lactation. Journal of Dairy Science 94: 1052-1057.
Guliksen SM, Lie, KI, Loken T, Osteras O. 2009. Calf mortality in Norwegian dairy herds. Journal of Dairy Science 92: 2782-2795.
Heinrichs AJ, Heinrichs BS, Harel O, et al 2005. A Prospective Study of Calf Factors Affecting Age, Body Size, and Body Condition Score at First Calving of Holstein Dairy Heifers. Journal of Dairy Science 88:2828-2835.
Love WJ, Lehenbauer TW, Kass PH, et al. 2014. Development of a novel clinical scoring system for on-farm diagnosis of bovine respiratory disease in pre-weaned dairy calves. PeerJ 2:e238. https://peerj.com/articles/238/
Stanton AL, Felton, DF, LeBlanc SJ, et al. 2012. The effect of respiratory disease and a preventative antibiotic treatment on growth, survival, age at first calving, and milk production of dairy heifers. Journal of Dairy Science 95:4950-4960.
USDA 2010. Dairy 2007, Heifer Calf Health and Management Practices on US Dairy Operations, 2007, USDA-APHIS-VS, CEAH, Fort Collins, CO. #550.0110 http://www.aphis.usda.gov/animal_health/nahms/dairy/downloads/dairy07/Dairy07_ir_CalfHealth.pdf
USDA. 2012. Dairy Heifer Raiser, 2011. USDA-APHIS-VS, CEAH, National Animal Health Monitoring System (NAHMS), Fort Collins, CO. #613.2012 http://www.aphis.usda.gov/animal_health/nahms/dairy/downloads/dairyheifer11/HeiferRaiser.pdf
Acknowledgements
The “Integrated Program for Reducing Bovine Respiratory Disease Complex (BRDC) in Beef and Dairy Cattle” Coordinated Agricultural Project is supported by Agriculture and Food Research Initiative Competitive Grant no. 2011-68004-30367 from the USDA National Institute of Food and Agriculture.