Study supports saline for Tritrichomonas foetus RT-rtPCR transport

A new Journal of Veterinary Diagnostic Investigation paper adds evidence that 0.9% sterile saline can stand in for PBS when veterinarians collect bovine preputial wash samples for Tritrichomonas foetus direct RT-rtPCR. The authors reported that saline was noninferior to PBS based on cycle threshold values across high, moderate, and low organism concentrations, including the assay’s lower-end detection range. In practical terms, that gives field veterinarians more flexibility in how they collect and ship samples for a disease that still carries reproductive and economic consequences for cow-calf operations. (pmc.ncbi.nlm.nih.gov)

The background here is important. Direct RT-rtPCR for T. foetus has gained traction because it can be run on preputial washings without prior culture and has been reported to offer strong sensitivity and specificity, with a limit of detection down to one organism per extraction in validated conditions. PBS became the standard collection medium for that workflow, but it’s more of a laboratory staple than a truck-stock item for many bovine practitioners. The study authors framed saline as an obvious candidate because it’s already widely available in ambulatory practice and is less burdensome to source in the field. (pmc.ncbi.nlm.nih.gov)

In the new trial, transport tubes containing either PBS or saline plus preputial washing material were inoculated with T. foetus at three concentrations over multiple weekly replicates. Mean Ct values differed by organism concentration, as expected, but not by transport medium, and the mean difference between PBS and saline was just 0.19 Ct, within the study’s noninferiority margin of 1.0 Ct. The authors concluded that using saline should not meaningfully affect RT-rtPCR Ct results. That’s a narrow technical finding, but it’s the kind that can remove friction from everyday testing workflows. (pmc.ncbi.nlm.nih.gov)

The broader literature points in the same direction, while also underscoring why transport conditions still matter. A 2025 study evaluating shipment conditions found that PBS and sterile saline were both important holding media for preserving T. foetus samples, and emphasized that RNA degradation during transit can increase the risk of false negatives. Earlier work on direct RT-qPCR also found no meaningful detection differences in PBS and TF transport media over short incubation periods and reaffirmed a limit of detection of one parasite per extraction. Taken together, the evidence suggests the medium choice may be more flexible than previously assumed, provided collection and shipping protocols are followed carefully. (pmc.ncbi.nlm.nih.gov)

There’s also a regulatory and industry angle. Nevada’s Department of Agriculture announced in February 2024 that its Animal Disease Laboratory would offer direct RT-rtPCR on samples collected in either PBS or saline, highlighting improved sensitivity, faster turnaround, and lower collection-device costs. Other laboratories and state-facing programs have likewise published guidance accepting saline, PBS, or other approved media depending on the jurisdiction and test purpose. At the same time, industry messaging is not uniform: Biomed Diagnostics highlighted separate AAVLD 2024 poster data suggesting its proprietary TF transport medium outperformed PBS for DNA preservation at low cell concentrations during transport. That doesn’t directly contradict the new saline-versus-PBS RT-rtPCR paper, but it does suggest that performance can vary depending on assay design, target analyte, transport interval, and whether the comparison is being made against a proprietary medium rather than another simple fluid. (agri.nv.gov)

Why it matters: For veterinary professionals, especially those serving beef clients, the study supports a more practical sample collection option without obvious loss of analytical performance. If saline is already on hand, clinics may be able to reduce delays, avoid special ordering of PBS, and standardize collection more easily across technicians and field teams. That said, the paper doesn’t mean every lab or every official state program will treat saline and PBS identically tomorrow. Trichomoniasis testing remains state-specific in many regulatory contexts, and accepted media, shipping windows, refrigeration requirements, and whether results count as official can differ by laboratory and jurisdiction. Veterinary teams will still need to match collection protocols to the destination lab’s current rules. (pmc.ncbi.nlm.nih.gov)

What to watch: The next step is whether more diagnostic labs, state animal health agencies, and interstate movement programs explicitly codify saline as an equivalent collection medium for direct T. foetus RT-rtPCR, and whether follow-on studies test that equivalence under real-world shipping stress, pooled sampling workflows, and official regulatory use cases. (pmc.ncbi.nlm.nih.gov)