Calves that are abruptly weaned and then shipped to feedlots are prone to respiratory infections from both viruses and bacteria, say scientists.
However low-cost preconditioning of calves before they are shipped can reduce bovine respiratory disease and death.
Two weeks of feed adjustment after on-farm weaning and before truck transport can cut feedlot deaths from infection by 50 percent.
“The stressful combination of weaning, shipping and introduction to the highly populated feedlot environment can often overwhelm the calf’s immune system, making it more prone to primary infection by viral agents such as BHV-1, PI-3, BRSV and BVDV,” said Reno Pontarollo, a Saskatoon animal science research consultant.
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“By themselves, these viruses are rarely fatal. However, they further compromise the calf’s immune system, enabling co-infecting bacteria such as H. somnus and M. haemolytica to gain the upper hand and deliver the fatal blow of what is called the bovine respiratory disease complex,” he said.
Weaning strategies might have a lot to do with an animal’s resistance to feedlot diseases, said Phillip Griebel of the Vaccine and Infectious Disease Organization.
He told producers attending the Termuende Research Farm field day near Lanigan, Sask., of a VIDO study in which 20 calves from a single herd in southwestern Saskatchewan were split into two groups.
The first group was weaned at the farm and placed on a hay and grain diet. The second was allowed to remain with their cows until just before shipping.
The groups were then reunited for a 31/2 hour trip to Saskatoon. On the day after arrival they were exposed to an aerosol respiratory spray of virulent BHV-1. Four days later the calves were exposed to M. haemolytica bacteria, known as one of the causes of shipping fever.
The resulting combination of virus and bacteria created a typical double pneumonia infection.
Eight of the calves that were abruptly weaned and shipped began to die, beginning 21/2 days after the second infection. Only four of the preconditioned calves died of the infection.
Griebel said the second infection acted, “almost too rapidly,” in the abruptly weaned calves.
“They were checked regularly. A calf that was fine at 9 would be dead at 11. Producers often tell us that this is happening, especially if someone gets into a wreck.”
Griebel said autopsies showed that the level of damage and swelling in the lungs of the abruptly weaned calves was not sufficient to cause death.
“It appears they died of septic shock. Treatment with antibiotics at the feedlot level might even have hastened their deaths,” he said.
Septic shock occurs when the immune system overreacts to a disease threat.
The preconditioned calves that died were killed by the damage the bacteria inflicted on the lungs.
Preconditioning is one of the keys to resisting BRD. But this is an old problem that needs more study, said Griebel.
Pontarollo said prior vaccination and preventive antibiotic treatment of calves upon feedlot entry are standard in North America.
“However, 20 percent of entrants still develop BRD-like symptoms and require further handling and antibiotic treatment. Some of these animals develop chronic pneumonia polyarthritis syndrome, never recover, and are lost in production,” he said.
Paul Himmelsbach and his family at Goodsoil, Sask., calve about 1,000 cows annually. They use both a modified live vaccination system that incorporates a cow vaccination and a fall calf booster and calf preconditioning process.
“I think all producers should be forced to retain ownership in at least 15 percent of their calves. They’d pretty quick cut out this dumping the animals off at the lowest cost of production they can. They’d be making sure they ship the best prepared calves the best they can,” he said.
Himmelsbach said producers “seem to forget that any losses in the system get passed back down the supply chain to the farmer’s price.”
Griebel said additional research is needed to determine the effects of abrupt weaning on feeder calves.
Pontarollo said it is possible that management techniques that target the virus and bacterial agents have reached their limit in economic
return.
“Perhaps now is the time to focus more on the animal and its environment. The concept of preconditioning calves is not new, but it maybe is time to reanalyze old ideas with the new technologies of genomics, proteomics and bioinformatics,” he said.
