In spite of advancements in vaccines and antibiotics, bovine respiratory disease (BRD) remains a costly problem for dairies, potentially causing long-term losses in productivity when affected heifers enter the milking herd. The incidence and severity of BRD in dairy cattle varies widely, making economic impacts difficult to quantify. But according to Elanco veterinarian Michael Overton, the overall cost in replacement heifers probably runs higher than most dairy producers realize.
During the recent BRD Symposium in Denver, Overton summarized some existing data and a recent study involving 104,000 heifers from 23 herds where managers consistently collected data on BRD.
The majority of BRD cases in dairy calves occur from birth to 120 days of age, Overton says, and in this data set, 36.6% of heifer calves had one or more cases during that time period. Calf raisers generally see the highest incidence of BRD during the first 30 days of a calf’s life, with another spike in morbidity occurring at and after weaning.
Overton notes that impacts of BRD in heifer calves include decreased rate of gain, a higher culling risk, delayed age at first service, delayed age at first calving and in some cases, lower future milk production.
In this study, the cost of raising a heifer with one or more recorded cases of BRD during the first 120 days exceeded those for healthy heifers by $212 to $237, depending on whether anticipated milk-production differences were considered. Those estimates greatly exceed previously published figures ranging from about $20 to $60 per head in BRD costs.
Overton added that individual herd costs will vary, and could be much higher than the average, depending on initial value of calves, level of BRD, culling practices, accuracy and promptness of diagnosis and treatment and any carryover effects during lactation.
Also during the BRD Symposium, University of California Davis Veterinarian Sharif Aly, BVSc, MPVM, PhD., discussed risk factors for BRD in dairy heifers.
Aly notes that BRD accounts for about 22% of heifer deaths on dairy operations in California. He and his colleagues at UC-Davis recently published results of a intended to determine how management practices on California dairies may be associated with (BRD) in preweaned calves. In this study, researchers visited a convenience sample of 100 dairies throughout California between May 2014 and April 2016, providing a study population of 4,636 calves.
In this study, housing factors positively associated with BRD were:
- Metal hutches compared with wood hutches.
- Calf-to-calf contact in calves greater than 75 days of age.
- Feeding Holstein calves less than 2.84 liters of milk or replacer per day.
- Lagoon water used for flushing manure under hutches compared with no flush.
Several management practices were negatively associated with BRD, including:
- Providing extra shade over hutches.
- Feeding calves at least 90% saleable milk or pasteurized milk.
- Feeding greater than 5.68 liters of milk or replacer per day to Jersey calves.
The UC-Davis team currently is working to release a risk-assessment app to complement their existing app for evaluating BRD prevalence in heifer operations.
Treatment Failure in Dairy Calves
Clinical signs of BRD in young dairy heifers tell only part of the story, and more objective diagnosis could help evaluate treatment success. During the BRD Symposium, University of Wisconsin veterinarian Terri Ollivett, DVM, PHD, outlined how individual and herd-level factors can contribute to treatment failures and how using thoracic ultrasound (TUS) to guide treatment protocols could improve measurement of treatment response and validate dosage regimens for antimicrobial drugs.
Effective treatment, Ollivett says, is a component of prevention and antimicrobial stewardship. However, she adds, many dairies do not measure treatment response, or typical measures based on resolution of clinical signs or records for retreatment rates and average treatments per calf. Using these measures, research suggests that 20 to 35% of treated calves need multiple treatments due to relapse of BRD signs.
Using TUS to detect non-aerated or consolidated lung lesions associated with pneumonia, Ollivett has found a high correlation between the amount of consolidated lung identified on TUS and gross post-mortem exams. Regardless of the clinical picture, she says TUS lung lesions in dairy calves are associated with reduced pre-weaning ADG, increased mortality and less milk production during the first lactation.
Ollivett says that by using a systematic clinical scoring system, such as the Wisconsin Respiratory Score, along with TUS, practitioners can define three BRD subtypes:
- Upper respiratory tract infections
- Clinical pneumonia
- Subclinical pneumonia
“Although the distributions of BRD subtypes will vary from farm to farm, we have found that approximately 1/3 of new cases are subclinical,” she says.
Noting a high incidence of relapse and retreatment, Ollivett hypothesizes that incomplete bacterial killing sets the stage for bacterial replication and relapse or recurrence of consolidation once the antibiotic pressure has been removed. Poor treatment response, coupled with misleading clinical criteria for treatment success puts calves at risk for future clinical disease and prolonged periods of slow growth. Instead of basing resolution of disease on clinical signs, she says, we should use resolution of lung lesions as the expected standard.
Implementing TUS-guided treatment protocols should improve response, resulting in fewer relapses and shorter duration of disease, improving calf welfare and decreasing cost, while ensuring treatments are effective at establishing a bacteriological cure within the lungs.
For more summaries from the BRD Symposium and Academy of Veterinary Consultants Conference, see these articles from BovineVetOnline: