In 2008, the Wisconsin Veterinary Diagnostic Laboratory (WVDL) validated a simple non-invasive technique to sample calves and cows for bovine respiratory disease (BRD).

The method uses a double-guarded mare uterine swab that travels through the bottom of the nose and samples the back of the throat in the pharyngeal tonsillar region.

Two swabs are collected from each animal with one swab placed in bacterial transport media (Amies with charcoal) and a second swab placed in viral, chlamydia, ureaplasma and mycoplasma transport media.

The samples are sent chilled overnight delivery to the laboratory and are tested (WVDL bovine respiratory disease panel) by real-time PCR for bovine respiratory syncytial virus (BRSV), bovine herpes virus-1 (BHV-1), bovine respiratory corona virus (BCoV), bovine virus diarrhea virus (BVDV) and Mycoplasma bovis.

The samples also are streaked on selective media and cultured in a 5 percent CO2 incubator for BRD bacteria, which includes Mannheimia haemolytica, Pasteurella multocida, Bibersteinia trehalosi, Histophilus somni and Truperella pyogenes.

Pharyngeal swabs work extremely well provided the animals are sampled when they first break with BRD (acute disease) and a sufficient number of animals (minimum of four) are tested so producers and veterinarians can get a snapshot of what BRD pathogens are involved in the respiratory disease outbreak. The technique is not satisfactory when subacute to chronic cases of BRD are sampled. The turnaround time is fairly rapid (one to three working days).

When pharyngeal swabs are coupled with antimicrobial susceptibility testing, the herd veterinarian can make an informed decision on which BRD vaccines and antimicrobial drugs should be used in their clients’ herds.

In many cases, the protocols already in place do not need to change, but the veterinarians have confirmation that their vaccination and treatment protocols are scientifically sound.

Material and methods

In 2010, the WVDL in collaboration with Merck Animal Health did a study on BRD in U.S. dairy calves. Veterinarians in the major dairy-producing states, which included the West (California, Idaho, Washington), Midwest (Michigan, Ohio, Indiana, Wisconsin), Northeast (New York, Pennsylvania, Vermont) and the South (Texas, Florida) were sent WVDL pharyngeal swab kits.

Veterinarians were instructed to sample Holstein dairy calves younger than 6 months old with BRD that had been sick for less than five days and had not been treated with antimicrobial drugs or received an intranasal or systemic BRD vaccine within 21 days of becoming ill.

Veterinarians were trained by Merck Animal Health technical veterinarians on the proper method to identify animals using the BRD scoring system developed by Sheila McGuirk at the University of Wisconsin – Madison.

Samples and the fully completed WVDL submission form, which included the age of the animals sampled, were sent chilled overnight delivery to the WVDL with a sufficient number of ice packs to ensure the samples remained cold during transport to the laboratory. Five to six calves were sampled from each premise experiencing respiratory disease. The diagnostic samples were tested using the WVDL respiratory panel.

Results

One hundred and ninety Holstein dairy calves from 32 different premises and 12 different states had pharyngeal swabs collected and sent to the WVDL for testing. There was no difference in the prevalence of respiratory disease pathogens found among the four different regions of the country, and there was no difference in the median age of the calves (7.8 weeks) when they were first affected with respiratory disease.

BCoV virus was found in 99 of 190 (52.1 percent) calves tested, and it was found in 25 of 32 (78.1 percent) herds. BRSV was found in 24 of 190 (12.6 percent) calves and 11 of 32 (34.4 percent) herds tested. BHV-1 was found in one calf, and BVDV was found in two calves.

There was no statistical difference in the prevalence of BHV-1 and BVDV, but there was a statically higher prevalence of BRSV and BCoV when compared to BHV-1 and BVDV (p less than 0.05). The prevalence of BCoV was statistically higher than the prevalence of BRSV (p less than 0.05).

Mycoplasma bovis was found in 101 of 190 (53.2 percent) calves tested and in 28 of 32 (87.5 percent) of the herds; Pasteurella multocida was found in 86 of 190 (45.3 percent) calves tested and in 29 of 32 (90.6 percent) herds.

Histophilus somni was found in nine of 190 (4.7 percent) calves, Mannheimia haemolytica in 22 of 190 (11.6 percent) calves and Bibersteinia trehalosi in one of 190 (0.5 percent) calves tested and five of 32 (15.6 percent), 13 of 32 (40.6 percent) and one of 32 (3.1 percent) of the herds tested, respectively.

There was no statistical difference between the prevalence of Mycoplasma bovis and Pasteurella multocida, but they were both found at a higher prevalence (p less than 0.05) than the other respiratory bacteria.

Possible associations between respiratory viruses and an increase or decrease in the recovery rate of respiratory bacteria were examined. There was no association between finding a respiratory virus and an increase or decrease in respiratory bacteria detection except for BCoV and Mycoplasma bovis.

Calves that were real-time PCR positive for BCoV were more likely to also be pharyngeal swab positive for Mycoplasma bovis (p less than 0.05).

Conclusions

BRD is a significant problem affecting calves in U.S. dairy operations. The results of this study found no difference in the prevalence of respiratory viruses and bacteria in four different regions of the U.S. BCoV, BRSV, Mycoplasma bovis and Pasteurella multocida, either alone or in combination, account for greater than 90 percent of the respiratory pathogens in Holstein dairy calves younger than 6 months old.

While the importance of BCoV as a primary pathogen in bovine respiratory disease is open to debate at this time, there is no denying that the virus is very common in U.S. dairy calf operations.  PD

Kathy Toohey-Kurth, Ph.D., Ogi E. Okwumabua, Ph.D., and Jennifer Godhardt-Cooper, MS, are with the Wisconsin Veterinary Diagnostic Laboratory, University of Wisconsin – Madison. Kathy Toohey-Kurth and Ogi E. Okwumabua are also with Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin – Madison.

• D.C. Sockett

• Wisconsin Veterinary Diagnostic Laboratory
• University of Wisconsin – Madison
• Email D.C. Sockett