With the advent of practical, affordable diagnostic tests, producers have been able to start unraveling the immuno-suppressive impact that cattle persistently infected (PI) with bovine viral diarrhea virus can have in their programs.

Now, the industry is getting an idea about how much PI costs, or how much avoiding it may be worth.

Consider a trial conducted by Bill Hessman, DVM, of Central States Testing and the Haskell County Animal Hospital at Sublette, KS. A feedlot client, Cattle Empire (CE), LLC, was wondering how prevalent the disease and pen-infection rate were in its operation. And to what extent were PI calves impacting their bottom line?

Ouch! According to Hessman, the cost of calves exposed to PI in that operation is $67.49/head, a total average cost across the entire population of $41.17/head.

That's based on 21,743 head across 240 pens.

One out of three pens exposed

The trial began in July 2004 at one of the firm's starter yards (10,000-head capacity) where cattle are limit-fed for 60 days and not implanted. Every animal was tested. PI animals were removed from some pens and left in others so CE owners, Paul and Roy Brown, could get a handle on how PI calves influenced pen health.

They found the prevalence rate of 0.4% was just slightly higher than that found in smaller trials. But at least one PI calf was discovered in 71 of the 240 pens, with a pen-infection rate of 31%. In other words, about one out of three pens had been exposed to a PI calf.

Despite longstanding industry conjecture, Hessman found the infected calves weren't more likely to come from one particular state than another (10 states were represented). What did increase the likelihood, though, was the order buyer.

Of the 15 buyers who bought 300 or more head represented in the study, the PI prevalence rate, by buyer, ranged from 0% to 2%. It turned out buyer behavior contributed to the fact some were more likely to send PI calves. In particular, Hessman said calves bought as singles or doubles through the auction were more likely to be infected.

The resulting pen rate of infection was just as startling. Of buyers purchasing three or more pens, the rate ranged from 0-70%.

The findings mirror those of a smaller trial (2,284 head in 24 pens) in which cattle were tested in CE's finish facilities. Using closeout performance to compare PI- and non-PI pens, CE found a prevalence rate of 0.31% and a pen infection rate of 21%. The economic damage in that trial was $47.43/head in the pens exposed to PI.

Keep in mind the bulk of the damage came from lost performance in cattle exposed to PI animals, not mortality and morbidity among infected animals. Hessman says, while many PI calves die early, some survive to slaughter.

Of those in CE's starter-yard trial, only 25.6% of the calves died during the 60-day starter phase. Of those, 64% of the deaths were due to mucosal disease and 27% to respiratory disease. In the smaller trial in the finish yard, 71% of PI calves survived to harvest.

Marketing PI screening

Though I'm not aware of economic data as extensive as this in other industry segments. I suspect the damage would be at least as significant.

Consequently, Hessman says cow-calf producers and stocker operators may find added marketability for PI-screened calves. Buyers may be willing to pay more for calves already tested.

Using CE's starter-yard trial, Hessman points out the $41.17 cost PI calves levied on the entire population is equivalent to about $8.23/cwt. on a five-weight calf. That's not what cattle feeders would likely be willing to pay, but at least part of that would provide added negotiation power for producers with screened calves or PI-free herds.

That's in addition to the economic advantages of identifying and removing PI animals from the herd to begin with.

It seems this kind of economic impact might make buyers more willing to share in the cost of screening calves they're considering for purchase.

It's already apparent that such major feedyards as CE are trying to wrap their arms around the problem. Judging by conversation at the recent Elanco Professional Stocker Operators Symposium, where Hessman presented this information, at least some of this nation's largest and most cost-progressive stockers also are in the midst of trying to sort out PI calves as early in production as possible.