Study supports saline for T. foetus RT-rtPCR transport

A noninferiority study published recently in the Journal of Veterinary Diagnostic Investigation suggests that 0.9% sterile saline can perform comparably to PBS as a transport medium for Tritrichomonas foetus RT-rtPCR testing. Using bovine preputial wash samples spiked at high, moderate, and low organism concentrations, the researchers found that saline’s normalized mean Ct was noninferior to PBS, with a mean difference of 0.19 Ct and a one-sided p value of 0.037. In short, the assay signal held up even when samples were submitted in a medium that’s far more familiar in day-to-day bovine practice. (pmc.ncbi.nlm.nih.gov)

That question matters because direct RT-rtPCR for T. foetus has been gaining traction as a faster, simpler alternative to culture-based workflows. Earlier work showed the assay could detect as little as one parasite per extraction in PBS and that PBS was not significantly different from TF transport media under several storage conditions. The appeal has been clear: no incubation, lower cost, and improved workflow. But PBS is more of a laboratory staple than a truck-box staple, so the field practicality of saline has been an open question. (pmc.ncbi.nlm.nih.gov)

In the new study, investigators collected preputial washings weekly for 10 weeks from bulls confirmed negative for T. foetus, pooled and processed the samples, then split them into PBS and saline preparations before inoculating them with T. foetus at 100, 10, and 1 organism per 100 µL. Mean Ct values differed by organism concentration, as expected, but not by transport medium. At the lowest concentration, mean Ct values were 30.2 for PBS and 30.7 for saline; overall, the upper bound of the confidence interval stayed below the prespecified noninferiority margin of 1.0 Ct. The authors concluded that veterinarians could reasonably expect similar Ct results when submitting preputial wash samples in saline versus PBS for this RT-rtPCR assay. (pmc.ncbi.nlm.nih.gov)

The broader laboratory landscape suggests the finding fits with practice patterns already emerging in parts of the U.S. The Nevada Department of Agriculture announced in February 2024 that its Animal Disease Laboratory would offer direct T. foetus RT-rtPCR on samples collected in PBS or saline, citing improved sensitivity, lower turnaround time, and lower collection-device costs. Wisconsin’s Veterinary Diagnostic Laboratory says samples submitted for T. foetus PCR can be sent in saline or lactated Ringer’s solution, while the California Animal Health and Food Safety Laboratory lists RT-qPCR options for samples received in PBS or lactated Ringer’s solution. Those policies don’t replace peer-reviewed validation, but they do show that laboratories have been moving toward more flexible submission media. (agri.nv.gov)

Industry messaging has also been pushing on the same operational problem. A 2024 Biomed Diagnostics announcement tied to AAVLD highlighted ongoing work on transport media for T. foetus PCR and framed specimen stability during field transport as a diagnostic bottleneck, particularly at low organism concentrations. That’s not independent expert commentary, and it should be read as company positioning, but it underscores how much attention transport media and sample integrity are getting in bovine reproductive diagnostics. (prnewswire.com)

Why it matters: For veterinarians and diagnostic teams, this is less about a marginal Ct shift and more about reducing friction in surveillance and regulatory testing. T. foetus remains a consequential cause of infertility and embryonic loss in cattle, and testing protocols can influence whether samples are collected correctly, shipped promptly, and accepted by the lab. If saline is validated more broadly, clinics may be able to rely on a more readily available collection medium without compromising assay performance, especially in ambulatory or rural settings where PBS may not be routinely stocked. Still, submission requirements remain lab-specific, so practitioners should follow the destination laboratory’s current instructions rather than assume interchangeability across all programs. (pmc.ncbi.nlm.nih.gov)

What to watch: The next step is external validation in routine field conditions, including shipping variability, pooled samples, and mixed regulatory environments, followed by updates to laboratory submission guidance if the evidence base continues to support saline as an equivalent option. (pmc.ncbi.nlm.nih.gov)