Jessica Laurin, DVM, Animal Health Center of Marion Co., Inc., Marion, Kan., has many stocker/backgrounder clients in her area on the edge of the Kansas Flint Hills. Speaking at the 2011 Annual Western Veterinary Conference, Laurin says, “Stocker/backgrounders in my area will purchase calves between 350-650 pounds to sell between 800-950 pounds, depending upon the market. Each year brings a new set of expectations and challenges.” Because of that, Laurin uses a variety of diagnostic tools and approaches for working with stocker/backgrounder clients.
“We utilize ear-notching for BVD at processing on arrival for purchased cattle,” Laurin says. “My producers and I discuss and choose cattle to test based on size, origin, and whether cattle are purchased at the sale barn as singles, less than five head per farm, or over five head per farm, and quality or price.” The first test offered is immunohistochemistry (IHC), where ear-notches are placed in formalin, stained, and read. IHC is a highly accurate gold standard test, and has a two day turnaround. Another test is the ELISA which has high accuracy, but a higher chance of false positives vs. IHC, but very quick turnaround time. “The cost of the ELISA test depends upon the supplier to the diagnostic lab, so this test is shopped around for cost as well as turnaround time,” Laurin explains.
The newest offering is real-time PCR which offers high accuracy, a higher chance of false positives vs. IHC, and fairly quick turnaround time. There are also labs that offer pooled PCR in groups of up to 50 ear-notches per pool, and then a positive pool is broken down and tested individually. Producer concerns are that it is labor intense, if lab reports are reported quick enough to be effective, and the logistics to make turnaround time practical. “This test can also be utilized in face of an outbreak if not run at the time of initial processing,” Laurin says. “Some order buyers offer to ear-notch test before the cattle are shipped. A BVD-positive test should be confirmed in two weeks with a repeated test to verify the animal is PI vs. TI (transient infection).”
It is important that on every respiratory case that organs other than the respiratory system are also examined. Laurin says to examine the abomasum, liver, kidneys, small intestines, cecum, mesenteric lymph nodes, if not more. “With respiratory deads, I check for abomasal ulcers, parasitic nodules, infection involving the intestines and mesenteric lymph nodes, and open the cecum to check for coccidiosis,” she says.
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.