Unscrambling The BVD Riddle

Bovine viral diarrhea (BVD). We know it's there and we know it's costing cattle feeders a ton of money. While numerous studies have looked into BVD, the consensus is that previous research has provided the industry with only partial insight into this complex disease. To get a better handle on the disease, feeders need to know more about its prevalence and cost impacts especially in regard to BVD persistent

Bovine viral diarrhea (BVD). We know it's there and we know it's costing cattle feeders a ton of money. While numerous studies have looked into BVD, the consensus is that previous research has provided the industry with only partial insight into this complex disease. To get a better handle on the disease, feeders need to know more about its prevalence and cost impacts — especially in regard to BVD persistent infection (PI).

That's why Cattle Empire Feedyards, LLC, Satanta, KS, entered into a series of multi-year, multi-tier studies designed to dissect this complex disease and address the largely unasked and unanswered questions.

Cattle Empire, in the feeding business since the early 1970s, includes three finishing yards (155,000-head total capacity) and two starter yards with a capacity of 15,000 head. The operation was founded by Paul Brown and his family. Today, son Roy is majority owner and CEO, while Ron Shortridge is a partner and CFO.

“One of the most basic questions yet to be answered relates to the BVD PI prevalence rate,” says Bill Hessman, a Sublette, KS, consulting veterinarian. He and Dave Sjeklocha, DVM, Haskell County Animal Hospital, are partners in Beef Production Management Associates, LLC, a consulting group also consisting of Shaun Sweiger, DVM, Edmond, OK, and Dan Stafford, DVM, Shiner, TX.

“In order to answer the cost question, one first has to know how often a PI animal may occur,” Sjeklocha says. “Also, is there a class of cattle or a region of the country in which PI cattle are more prevalent? Is there a time of year in which PI cattle are more prevalent?”

And, of course, what are the costs associated with having a PI animal in the feedyard? What degree of treatment and prevention measures do these costs warrant?

Shedding more light

Previously, Guy Loneragan of West Texas A&M University (WTAMU) found feedyard PI prevalence to be about 0.17% (1.7 PIs per 1,000 head). In his 6,000 head study, he found pens that included a PI animal had 35% higher morbidity than pens with no apparent exposure to PI animals.

“Even more interesting was the non-PI pens placed adjacent to the pens with a PI animal in them also had 35% higher morbidity,” Sjeklocha says. The landmark WTAMU study also showed 3% of railers and deads are BVD PIs.

Table 1. Performance of persistently infected (PI) and non-PI (NPI) calves
Head count Weight in (lbs.) Weight out (lbs.) Weight gain (lbs.) Days on feed ADG Consump. dry (lbs.) F/G (deads in) Cost of gain (deads in)
NPI 1,731 571 1,051 405 180 2.25 14.02 6.26 .691
PI 553 574 1,040 357 177 2.00 13.75 6.94 .767
p-value .76 .70 .04 .58 .07 .53 .02 .05
Table 2. Health of PI and NPI calves
Head count % Morbidity First relapse rate Second relapse rate Average No. of treatments Med $/Head Med $/Head treated % Mortality % Railers
NPI 1,731 49.52 46.04 55.44 1.72 25.40 52.80 6.96 6.34
PI 553 42.31 43.74 54.84 1.68 23.05 55.41 10.37 6.39
p-value 0.22 0.71 0.93 0.76 0.43 0.24 0.14 0.97

Source: Beef Production Management Associates, LLC

Cattle Empire Feedyard: BVDV PI Prevalence and Performance Study

“This tells us PI cattle are more likely to become chronics or die than non-PI cattle,” he adds. “It also shows the effects of a PI animal will cross the fenceline, and PI animals make up a higher proportion of the deads and railers.”

Such research has stimulated Brown and Shortridge to dig into more questions related to BVD PIs — and the potential for helping their feeding customers become more profitable. In October 2003, they teamed up with Boehringer Ingelheim Vetmedica, Inc., providing 2,284 head of “high-risk” calves. The 572-lb. calves came from the Southeast via five different order buyers.

Upon arrival, the calves were not commingled. They were placed into lots according to load and/or buyer. Each of the 24 study pens ranged from 60-150 head. All calves were ear-notched at initial processing and PI tested using the immunohistochemistry (IHC) test.

Seven PI calves were found in the study group (0.31% or 3.1/1,000 — nearly double the Loneragan study's rates).

“In our trial, five of 24 — or 21% of the test pens — had at least one PI animal,” Hessman says. “Three pens each had one PI and two pens each had two PI calves.”

The PI and non-PI pens were randomly placed throughout the feedyard, with the PI status of adjacent pens unknown. Health and performance parameters were tracked through the finishing period (Tables 1 and 2). Feedyard workers weren't told if pens were PI positive or PI negative.

Assessing the costs

The study's outcomes show there was a statistical difference in the weight gain, feed conversion (F/G) and cost of gain (COG) categories. Average daily gain (ADG) was very close to statistical (a p-value of 0.07 — see sidebar on page BF4). The NPI treatment group gained 405 lbs. through the feeding period.

Total difference in the COG between PI and non-PI (NPI) pens was $7.60/cwt. gained. Therefore, cattle that did not have a PI animal in their pen had a $30.78/head cost advantage (405 lbs. gained, $.076/lb. advantage) over cattle with a PI animal in their pen.

Hessman says it's important to note that because the spatial association of the adjacent pens' effects on the control group (NPI pens) was not known, this cost per head would most likely be a conservative figure.

The PI animal causes a distinct increase in mortality in the PI pen — with the majority of the mortality increase occurring in the first 30 days on feed, he says. Based on these data, it's apparent there's a substantial benefit to feeding cattle that are PI free, Hessman adds.

Questions yet to ask

Increased costs associated with PIs occurred in part from increased mortalities, but mostly from poorer feed conversion, Hessman explains.

“Pens with PI animals converted 11% less efficiently than NPI pens and the COG in PI pens was 11% greater,” he says. “Other studies have shown an increased morbidity associated with PI animals, but in our study we only saw a numerical increase in morbidity in the NPI pens.”

The Cattle Empire study also showed more treatments in the NPI group, which is different than what has been reported in other studies.

As a progressive cattle feeder, Brown is anxious to make the management changes needed to whip BVD in his feedyards. He's working to gain answers to the additional questions the initial phases of this study stimulated.

For instance, Brown says, “since there's a substantial financial advantage to feeding PI-free cattle, where can a steady supply of PI-free cattle be found?”

Also, he asks, since it's been shown the BVD virus can be spread across the fence to adjacent pens, does that mean feedyards need to develop PI-free zones in the yard?

“How serious is the threat when a calf from a PI-free pen spends time in the hospital with a PI calf?” Brown asks. “Is the virus spread more readily across the fence or through a fenceline water tank?”

Since it's difficult to locate a steady supply of PI-free cattle, he wonders if it's cost-effective to test and remove PI cattle upon feedyard arrival.

Second-phase underway

Upon completion of the Boehringer Ingelheim-sponsored study, Hessman presented the data to Brown and Shortridge, asking them to provide 20,000 head of cattle for further experimentation.

“Brown and Shortridge could see the potential for helping their feeding customers become more profitable. With the help of Fort Dodge Animal Health, they readily agreed to finance Hessman's experiment,” Sjeklocha says.

That two-phase, 20,000-head study began last August. It was designed and developed by the Beef Production Management Associates group along with Tim Murphy, nutrition consultant for Cattle Empire. It includes a starter phase and a finishing phase using more high-risk Southeast calves.

At considerable expense, Hessman set up his own laboratory for the study. He's using the Antigen Capture ELISA (ACE) test — as this test allows for a quicker return of the test results than the IHC test (which takes 7-10 days for results). The ACE test provides results in less than 24 hours. Hessman's use of the ACE test in this study has validated it for this type of use.

The study allows Hessman to compare health and performance parameters associated with having a PI animal in the pen with:

  • Pens in which the PI animals were removed.

  • Pens in which there was no apparent BVD-PI exposure.

“It also allows him to track the effects of having previously unexposed pens adjacent to pens in which the PI animal is still present and pens in which the PI animal is removed,” Sjeklocha adds.

Further, Hessman will be able to assess any differences that may occur due to fenceline and water tank contact vs. strictly fenceline contact. He can also track the effects of sending a PI animal through the hospital system.

As of this writing, the starter phase of this trial is completed and the data is under evaluation. The finish phase of the trial should be complete by August with plans to publish the results in BEEF magazine next fall.

For more information, contact Bill Hessman, DVM, Haskell County Animal Hospital, 620/675-8180 or e-mail him at hcah@wbsnet.org; or call Cattle Empire Feedyards, LLC at 620/649-2235.

Consider the numbers…

For readers not familiar with statistical analysis, Dave Sjeklocha, DVM and feedyard consulting veterinarian from Sublette, KS, says scientists generally require a “p” value of 0.05 or less for a difference to be considered significant.

Taking this into consideration, it's somewhat surprising to see in the Cattle Empire BVD-PI study that none of the health parameters had a significant (true) difference, even though there is a numerical difference.

“It's plausible that had this trial included more cattle than the 2,284 head, the health parameters may have shown a significant difference,” Sjeklocha says. “However, there are some significant differences in the performance data.”

Weight gain, conversion and cost of gain are all statistically significant, favoring pens with no PI cattle in them. Average daily gain is very close to being statistically significant.

Sjeklocha wrote an article for BEEF in August 2003 called “Question Everything.” It explained statistics and their application to cattle production.