By Gary DiGiuseppe
New feed, new weather, new pens and new herdmates all add up to stocker calf stress. Timely vaccinations will help.
T he older a calf is, the better it is at handling stress. And that's a good thing because, as Mark Spire, D.V.M. points out, once they leave the farm, calves are in for a lot of stress.
Spire, who is technical services manager for Merck Animal Health, says the stress associated with weaning for a newly-weaned calf is a one-time event. Once that traumatic event has taken place, the calf starts physiologically responding to it.
"If they don't get additional stressors placed on them, their little ‘ship of life' will right itself pretty much in 5 to 7 days," Spire says. They'll then be better able to handle the pathogens that come their way and the inoculations they receive to protect them from those bugs.
The stocker calf is older, hardier and better able to respond to life's challenges. Those challenges will include being passed from a ranch or from a backgrounding operation to new owners via the sale barn, with handling every step of the way.
Spire says, "We've taken them from a single ration into a period where they may or may not get good groceries. Water's limited and there's crowding. They have to adapt to a new feed, new weather, new pens and new herdmates. We just keep stacking stuff on those calves, and stress just compounds and compounds."
So while the weaned calf will typically respond quickly to the single stress separation from its mother, the stress piles up on the stocker calf. Spire says the inflammatory proteins in its system increase, its electrolytes become unbalanced and the beneficial bacteria in its rumen turn over as it tries to adapt to the new environment. The animal also has to re-adapt to a new social structure.
"Cattle are herd animals. Every group is going to have a social structure in it and they have to re-establish that social structure," Spire says. "All those together create an environment where it's rich for bacteria or viruses to proliferate."
Sharing among stockers
Although the vast majority of the cattle will not already be harboring pathogens upon entering the environment, studies show 12 to 15 percent of the calves will come in carrying various pathogens. When the calves are mixed, the number of calves carrying those organisms increases. In about a month's time, the vast majority of them will have a new set of pathogens that they may not have had at arrival. Among the bacteria they'll "share" are Mannheimia haemolytica, Pasteurella multocida and/or Histophilus somni, and the viruses include IBR, BVD or bovine respiratory corona, and Mycoplasma bovis.
While most loads of cattle that arrive have few or minor issues, Spire says 2 to 3 percent of load lots of cattle will experience death loss of as much as 40 percent. It's not because a particular vaccine failed to protect the animals. In many cases, they are persistently infected (PI) animals that are already harboring deadly diseases, such as BVD, that they contracted in the womb.
Spire says he tested about 1,200 calves that were collected by Merck over a 6-month period and about 1 percent were persistently infected with BVD.
"That's a significant number," he says, "because that virus sheds out of that calf and goes to all the rest of them. We found BVD in load after load of cattle. It shifts our death loss up and shifts our sickness levels up and makes it tougher for crews on the other end to manage stocker calves in those situations."
"The nose of the calf," says Spire, "is a crowded place." A recent study conducted by Merck Animal Health examined high-risk calves that were collected from at least 20 operations in Tennessee, processed at an auction market and then shipped to a Nebraska feedlot. The calves had samples taken from their noses to check for M. haemolytica, P. multocida, H. somni and M. bovis, first at the sale barn and then upon arrival in Nebraska, and again 7, 14, 28 and 42 days after arrival.
The calves were not given any antibiotic upon arrival at the feed lot. The rate of spread varies with the organism. Few calves had either M. bovis or M. haemolytica in their nasal passages in Tennessee. The number of M. bovis-positive calves increased 2 weeks after arrival at the feedlot and peaked after a month.
On the other hand, the calves carrying M. haemolytica increased from the initial mixing of the cattle and peaked at 14 days. This coincided with the number of sick calves observed at the feedlot.
The number of calves found to carry P. multocida also rose steadily after arrival and peaked at 28 days, when 51 percent of the calves were positive.
H. somni-positive calves rose more slowly than the other 3 organisms, peaking at day 42 with 53 percent of the calves positive.
Spire says this shows organisms frequently associated with pneumonia are present in the nasal passages of calves and notes it's easy for the pathogens to migrate from the upper respiratory tract deeper into the animals' lungs following periods of stress or viral infection, or when the calf's immune system is compromised.
He says, "Setting up a treatment program is a lot more difficult because of the differences in rates and timing of spread of these organisms from one calf to another. In the case of Mannheimia, you would want to select a drug that is highly effective and delivered at arrival or shortly after receiving a group of calves. For Mycoplasma or Pasteurella, a drug used up front would be of limited value due to the low and slow spread of these 2 potential pathogens. Delivery of products to aid in controlling Histophilus might be targeted to even later in a receiving program."
Spire suggests producers select the antibiotic that offers the longest persistence in the animal's tissues. He says stocker calves will receive what's called "metaphylaxis," the timely mass medication of a group of animals to eliminate or minimize an expected outbreak of disease. "We'll treat them right at arrival," he says. "There's no guarantee that you're going to sterilize the nasal passage on these calves. You'll reduce the numbers, but they tend to spring back."
He also says all drugs may not work against all bugs. Of the 12 to 15 percent of calves that will be positive at arrival for M. haemolytica, around one quarter of them — 4 percent of the overall herd — are carrying organisms that are resistant to 2 or more antibiotics.
"That's a concern," says Spire, "because if that multidrug resistant bug becomes the dominant pathogen that's going through a set of calves, we don't have effective antibiotics for them."
But while you don't want to overtreat the animal so the resistant bugs will be selected out, "you don't want to kill them with kindness, either," he says. "In some cases we have producers that will rehandle cattle after a week or 10 days to vaccinate them again because they didn't feel like they got vaccinated up front, or they didn't take those vaccines."
That adds yet another stressor to the already-stressed animals by reshuffling their social order and changing their intake for several days. It may also increase injury or bruising in those animals. All these things may create a more inflammatory environment and a potential for more issues.
Stressors cause a biological reaction that magnifies the impact of the pathogens that are present. The stress causes the release of reactive proteins in the body called proinflammatory cytokines and, says Spire, "We've found viruses and bacteria like those in their environment. It's almost like putting them on steroids and we can see the viruses and bacteria change. They replicate, and in some cases we can see the pathogenicity change, so we actually start making a tougher bug."
The timing for additional vaccinations is up for debate. Spire says some research shows the ideal time for stocker calves to receive them is right up front. Other studies indicate if the booster is delayed, there's no difference in the number of sick or dead calves. But given the uncertainty, he's in the first camp, saying, "My preference is to allow that calf to start responding to our vaccines right up front when we get them, because in the majority of cases we don't know the vaccination history in stocker calves, so we're going to bring them into conformity with what we know works in a particular operation."
Weather, food and parasite stress
Another source of stress is the weather. Fall-weaned calves have to deal with cold nights and warm days, and if a chilly afternoon is coupled with rain, the animals can't take in enough energy and may not respond as well to vaccines or treatment.
Some pathogens also appear to proliferate in cold weather, such as coronavirus. "It'll be kind of like the common cold," says Spire. "For about 10 days while there's an infection, it'll suppress the immune system and allow something else to happen." He says it's present in about 20 percent of cases where producers are experiencing other health problems in cattle. There's no vaccine for it, so management is key.
An additional environment-related factor is nutrition. "Droughty cattle won't have the protein levels or the energy levels in them" when they arrive at the feedyard, Spire says. "A lot of times, they're in a marginal state of metabolism, where they're just holding on. We see trace minerals decrease."
It takes time for minerals to accumulate in the bodies of the cattle. A shot only provides temporary respite. It also takes 9 to 10 days for the rumen bacteria to adapt to new rations, and if the ration is not well balanced, there could be further adjustment problems.
Spire says, "If I do things that are going to disrupt the intake pattern of those animals — that's rehandling those cattle, dumping new cattle in, irregularities on the time I feed cattle — all those things can end up taking longer to get those cattle adapted. When they're adapting they tend to be on a negative energy balance. When that happens, we don't have the immune system functioning at its fullest, and the calf is just not going to respond."
And there will also be a side effect produced by parasite control. Spire says following deworming, it takes the immune system of a stocker calf 10 days to 2 weeks to adjust to the reduced parasite load. Think of it as a set of scales, he says. "If it's off balance, it's got to reset itself to where it's able to respond to viruses and vaccines better."
Says Spire, "Many factors contribute to poor health responses in newly weaned or received calves. Many are simple management errors that can be avoided. If management errors such as introducing persistently infected BVD calves, mixing cattle shortly after arrival, feeding irregularities and/or inappropriate vaccine use are added as additional stressors, the chances increase that populations of bacteria, viruses and mycoplasma that come in through and often reside in the noses of cattle can start to proliferate, resulting in a health wreck. Think about management from the calf's perspective. How would you like to be managed?"