June 1, 2006
There's no way around it: co-mingling and transporting cattle stress them. And any stress can lose money. Since that's the case, University of Arkansas cattle researchers have been looking at several ways to reduce impacts on the animals.
“Stocker cattle bought from Arkansas market channels are frequently stressed,” says John Richeson, Extension Beef Improvement Program associate. “Without a doubt, that stress negatively affects an animal's ability to respond to vaccines. Stressed cattle have a weaker immune system and lower response rate.”
Researchers studied two groups of high-risk stocker cattle. One group was given a five-way modified live vaccination (MLV) on arrival. For the other group, the vaccination was delayed 14 days — the only difference between the two groups.
“We took 528 crossbred calves out of an Arkansas livestock barn and received them at the station,” said Richeson, who spoke at the recent Livestock and Forestry Branch field day outside Batesville, Ark. “The two treatments were applied to those cattle, which were randomly selected for one of the treatments when they arrived.”
To help monitor performance during the receiving period, the cattle were weighed several times. Fourteen days after arrival, the delayed vaccination calves had greater weight gain. The same was true for the overall 42-day receiving period. This finding was part of a trend showing cattle better handle transport, immunity buildup and acclimation to new surroundings when MLV vaccination is delayed.
“When we give cattle a vaccine, we want them to mount an immune response. What's common is to get a load of cattle and do all the processing, vaccinations and everything else almost immediately. We wanted to see what would happen if we let the cattle come in, rest for a couple of weeks and get over the market stresses and any sickness they already have and then vaccinate.”
Upon arrival, many of the stocker cattle have most likely been exposed naturally to the viral strains contained in a five-way MLV vaccine.
“Another thought behind the study is when you give a vaccine, especially a MLV, to a high-risk, stressed animal, it can have negative effects. That MLV is behaving similarly to the actual virus. While it's modified and isn't as harsh as a real infection, it's still causing cattle's immune systems to respond and develop antibodies.”
Titer levels, which provide an indication of an animal's response to a vaccine, were also looked at.
“We wanted to check IBR Titer levels on the same day post-vaccination. Since one group was given the vaccine when they arrived and the other group on day 14, we compared the Titer levels for the arrival group on day 14 and for the delayed group on day 28. That's an equivalent post-vaccination Titer testing date.”
On day 28, the delayed vaccination cattle showed greater IBR Titer levels.
“If the management situation allows, perhaps it's better to delay vaccination. The combination of greater performance in addition to the overall better response to vaccines later in the feeding period would seem to justify that.”
How about the financial incentive to delay the vaccination versus the threat of contracting a disease? How can those be put on the scales together?
“That's the huge issue. We aren't really saving money on input costs — the vaccine is still being given. But we could be earning dollars through better performance by delaying that vaccine.
“As far as animals contracting BRD during the proposed 14-day delay, high-risk cattle often are previously exposed at the auction barn to the viruses the MLV fights. The BRD viruses — whether IBR, BVD, PI3, or BRSV — are a precursor to bovine respiratory disease.
“What causes cattle to become sick or die from BRD is typically the bacterial infection that comes later. The bacterial infection is secondary, after the cattle try to fight off the initial virus. The pasteurella bacteria — commonly occurring in cattle's nasal areas and lungs at low levels — take advantage when the immune system is compromised by a virus. That allows the bacteria to increase replication and causes major problems with morbidity and mortality.”
While viral vaccines do nothing to fight against bacteria, there are some bacterins on the market. “There's even one for pasteurella that has shown some effectiveness.”
What about response rates?
“Say you bring 100 head of stocker cattle in. Even under the most ideal conditions, if they're low-stressed and low-risk, perhaps only 70 to 80 of the animals will develop the desired immune response to the vaccine.
“In high-risk cattle, only half the cattle may get to the desired immunity level/antibodies needed with one injection. In those cases, you may need to revaccinate and improve on that 50 percent, maybe add another 25 of the animals.”
Many of the questions Richeson takes on the study are in the context of cow-calf operations. “Producers should understand this is strictly for stocker cattle — the phase after the cow-calf segment. It doesn't apply to pre-weaned calves at all. It only applies to calves that are weaned, sold and shipped to the next phase.”
Richeson also fields questions about giving a MLV to cows. MLVs can cause cows to abort and can lead to other problems. However, “there are some new MLV vaccines that can be given to open cows if directions are closely followed.”
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