Laurin typically send in lungs, trachea, heart, liver, abomasum, ileum and mesenteric lymph nodes on all respiratory cases. The best conformation for a PI calf or chronic TI BVD infection is the mesenteric lymph node with the ileum.
Cultures are typically finalized within three days, but most labs will report if something has grown within the first two days, and a sensitivity can be produced within a day. On calves under 550 pounds, a nasal swab can be utilized as a practical replacement for deep guarded nasal swabs or a tracheal wash. Accuracy is dependent upon technique.
Respiratory PCR Panel (new)
“The lab I most commonly use started offering the respiratory PCR panel this fall,” Laurin says. “It is very sensitive and offers a quick turnaround time.” The panel report includes Mycoplasma bovis, Chlamydia, BVD, BRSV, coronavirus, IBR, and PI3. When one is reported as positive, the lab then reports a cycle count. A ct<30 means higher amounts of virus, and a ct>30 means very low amount of virus present. For certain viruses, it is best to confirm a positive with virus isolation.
VI has a slow turnaround time, with up to 10 days to confirm a report. BRSV cannot be tested this way, and IBR may be gone within the animal too quickly to be tested this way. “Before PCR testing was offered, I would collect blood from three to four animals that appeared clinical for BVD and use virus isolation to confirm BVD infection within a pen,” Laurin notes.
Slow turnaround time makes it hard to utilize Mycoplasma culture for practical recommendations. “I use it after a positive PCR if I think there is clinical evidence of Mycoplasma and want further information,” Laurin says.
It is useful when there are a higher number than expected of realizers or chronics, especially if cattle are not responding and the yard is not utilizing tetracyclines in any treatment protocols.
Virus titers are not very practical in terms of time and allocation of labor, but may be useful as a follow up test to PCR identification of IBR or BRSV.
Respiratory FA Testing
Fluorescent antibody (FA) can be run on fresh lung samples to detect BRSV, PI3 and BVD. It’s not as sensitive as PCR, but the result is not as confounded by vaccination. FA has a fairly quick turnaround time.