Because of the low prevalence of PI animals, not all producers can justify whole-herd PI screening. However, if ranch history, a significant breech in biosecurity or changes in production practices increase the risk of PI cattle being present, a protocol to screen the herd can be defended based on the likelihood of economic return.

A new effort of the Montana Beef Quality Assurance program is the Montana BVD-PI Herd Screening Project. This past year, the project funded through the Montana Beef Network, has overseen the screening of nearly 35,000 head of cattle from 65 Montana operations. Of those, about 80% were calves sampled at spring branding. The remainders were replacement heifers (10%), weaned calves (5%) and breeding bulls and dams of PIs.

Only 24 PI cattle were found — with one rare “PI-pair” (a first-calf heifer and her calf). But project managers understand the 2006 Montana project didn't represent a statistically valid sampling of the state's cattle population.

Interestingly, the majority of PI calves (62%) were born from first-calf heifers. Conventional wisdom dictates that because BVD virus impinges on reproductive function, it's less likely a rancher will find an older PI cow. Over time, late-breeding cows or those that fail to breed are usually culled from cow herds; therefore, ranchers, through common-sense management, tend to rid PI cows from their herds.

This is one reason why buyers of older cows — especially “put together” cows — should be concerned about bringing disease onto their operations.

The Montana project contracted with Animal Profiling International (API), Portland, OR, as its laboratory collaborator. API promises “next business day” screening results.

API is using “pooled” polymerase chain reaction (PCR) analysis. Their lab pools samples from multiple animals (usually 28 or less) in a strategy that takes advantage of the high sensitivity of the assay while reducing the cost per animal tested.

This screening technique is a “sensitive and specific method of screening cattle for persistent infection with BVDV,” confirms James A. Kennedy, DVM, MS, in the November 2006 Journal of the American Veterinary Medical Association. Kennedy is head of the CSU Veterinary Diagnostic Laboratory, Rocky Ford Branch, and a pioneer in statewide BVD-PI screening programs.

Given recent advances in BVD-PI diagnostic techniques and reduced screening costs, some cattle feeders are screening all calves coming into their feedyards for PI status. Some feeders are asking ranchers to screen their herds before or at weaning.

Calves, heifers and bulls are also showing up on video sale listings, market Web sites and sale literature as being “BVD-PI-screened” or “BVD-PI-free.”

Most observers believe it's a misnomer, however, to advertise cattle as being “BVD-Free” — as it's nearly impossible to guarantee any animal or herd is free of transient BVD virus. In fact, care should be taken when guaranteeing cattle are “BVD-PI-free,” as no sampling protocol or analytical procedure is immune from error and can be considered 100% perfect.

Nevertheless, Montana project managers have had calls from out-of-state cattle feeders asking for a list of ranchers who have participated in the screening project. They understand the risk of receiving PI cattle from screened herds is nearly nil, for all practical purposes.

It's highly recommended that all ranchers — both seedstock and commercial — who market breeding cattle, screen for PI status prior to sale. If the animals' health management history is unknown, buyers have every right to ask for PI-status screening prior to delivery.

Montana project managers don't necessarily recommend perpetual or annual whole-herd PI screening on a cow-calf operation. They suggest ranchers who whole-herd screen and don't find a PI animal can be “reasonably assured” of minimal PI-risk given the following basic management:

• Vaccination protocol based on veterinary advice.

• A sound biosecurity program that includes screening all herd additions before they enter the operation.

• A firm understanding of the BVD virus and disease transmission.