What is in this article?:
The prevalence of cattle persistently infected with Bovine Viral Diarrhea (BVD) virus continues unabated in the feedlot and stocker pasture.
Performance Is The Chief PI-BVDV Thief
“Our study was the first to look at performance, trying to understand the process of how BVDV works in the background robbing the metabolic process,” Hessman says.
He’s talking about 15,438 head of high-risk, sale-barn calves assembled in the Southeast and delivered to a starter yard in Kansas. They comprised 167 lots and were allocated among 172 pens for 66 days of backgrounding. For the record, 21,743 head arrived at the yard initially, but lots with fatalities prior to processing, or from which samples were not obtained, were excluded from the final analysis. Testing revealed 82 PI-BVDV animals in 70 lots for a prevalence rate of 0.50%.
The BVDV thievery revealed by the study is stunning.
“This study revealed that there is a detrimental impact from exposure to PI-BVDV cattle in a feedlot,” Hessman says. “Economically, this amounted to $93.52/animal in this study population at this feedlot. The largest segment of this loss was the result of performance losses of $88.26/ animal, and the balance of $5.26/animal resulted from an increase in the fatality percentage.”
Hessman explains that, though significant, the level of impact was reduced when disregarding outliers that had the most devastating effect. In the real world, unfortunately, removing outliers is not an option.
Hessman also points out the economic impact stems from the fact that BVDV infection is often subclinical – as much as 70-90% by some estimates. Animals persistently or acutely infected rob dollars through inferior performance, but you never know it.
In his study, Hessman says, “Feed efficiency or feed conversion may have provided the greatest impact to the economic outcomes because unexposed cattle had converted feed into body weight 55% more efficiently than did cattle with direct exposure.”
Hessman points out the cattle were not implanted and were limit-fed a moderate NEg ration.
“The effect on feed conversion likely represented the maximum difference, because this study represented only the first 66 days of the feeding period, and there would likely be some compensatory gains in the remainder of the feeding period,” Hessman explains. “On the other hand, there is no compensation for fatalities (deads-in calculation), and differences in fatality percentages among the exposure groups may have increased throughout the entire feeding period.”
Moreover, Hessman says, “A great number of animals exposed to PIs outperformed the mean of non-exposed cattle … The variability among PI animals can lend itself to misleading outcomes.”
For that matter, Hessman says some folks look at statistical significance and miss the point. He remembers another BVDV pioneer, Robert Fulton at Oklahoma State University, explaining the differences between statistical significance and biological significance.
In Hessman’s study for instance, the cost of gain for cattle exposed to PI animals (PI animals in lot on arrival and not removed; adjacent pens contained PI and non-PI cattle) was $6.31/kg, compared to $2.09/kg for cattle in pens where there were no PI animals in the lot on arrival, or in adjacent pens on arrival. Weight gain of the PI-exposed cattle was 34 kg compared to 50 kg compared to the unexposed ones (Table 1).
|Average treatment #||1.79||1.77||1.72||1.58||1.66|
Treatment Groups shown in Table 1:
PI – PI cattle in lot on arrival and allowed to remain in lot throughout the study; adjacent pens contained a mixture of PI cattle and non-PI cattle.
PIR– PI cattle were in the lot at arrival, but removed from the lot within 72 hour after arrival; adjacent pens contained a mixture of cattle from lots with no PI cattle at arrival or from which the PI cattle were removed within 72 hours after arrival.
NPIE– Non-PI exposed cattle in which there were no PI cattle in the lot at arrival but cattle were exposed because an adjacent pen or pens contained 1 or more PI animals.
NPIER– Non-PI exposed cattle in which there were no PI cattle in the lot at arrival but cattle were exposed because an adjacent pen or pens contained cattle from which the PI cattle were removed within 72 hours after arrival.
NPIU– Non-PI unexposed cattle in which there were no PI cattle in the lot at arrival and adjacent pens contained cattle from lots in which there were no PI cattle at arrival.
“This comparison shows the PI cost in the feedyard, to a yard that does not have any PIs on arrival – essentially the true cost of PI animals in the yard,” Hessman says.
Though it’s always a fool’s errand to infer results between studies or classes of cattle, Hessman says logic suggests that the prevalence of PI-BVDV is greater in the stocker sector than in feedlots simply because lighter, younger cattle are most likely to die from persistent BVDV infection.
“Prevalence is higher in younger animals because PIs have a greater mortality rate and tend to die out of the population over time; therefore, PI rate tends to decrease with age,” Hessman explains. “You’ll see the most PIs in a group at birth. Over time, as some PIs die, the prevalence will decrease.”
Spun another way, Hessman says, “There’s almost a linear reduction in PI prevalence as cattle weights increase.”
As an example, the prevalence among 2-weight calves was 0.64%; it was 0.38% for 5-weights, and .25% for 7-weights.
Plus, Hessman explains, younger, lighter cattle are more susceptible to infection and more likely to be commingled, another major factor associated with BVDV infection.