Cattle that survived the October blizzard in western South Dakota may face many health problems in the weeks ahead, says South Dakota State University Extension Veterinarian, Russ Daly
Prolonged stress placed on animals, especially younger animals, due to weather events results in increased cortisol levels in the animals' bloodstream, which can have profound effects on the immune system, he says.
"Long-term stress can have the effect of shifting the immune system towards production of antibodies and away from cell-mediated responses. In practical terms, this means that the body has less of an ability to respond to diseases caused by viruses," Daly says.
In growing cattle, respiratory diseases are often caused or started by Infectious Bovine Rhinotracheitis (IBR, or "red-nose", Bovine Respiratory Syncytial Virus (BRSV), and Bovine Viral Diarrhea Virus (BVDV).
"Respiratory diseases in cattle generally have an "incubation period" of 7-14 days. Therefore, ranchers might expect that cattle affected by the blizzard could break with these illnesses over the next two weeks."
Weaned calves may be more susceptible to coccidiosis as well.
"This condition will present as bloody stools, along with dehydration and depression in more severely affected calves. Prompt identification of affected calves and treatment with individual or feed-based medications is important," he says.
Daly advises ranchers to consult with their veterinarians whether feed- or water-grade antibiotics, especially in weaned calves, would be appropriate for any of these conditions.
"In spring calving herds, the storm hit in the midst of ranchers' normal preparations for weaning. Herds were in various stages of the process, anywhere from having calves weaned already to calves having their first pre-weaning vaccination, to calves that had not had pre-weaning vaccinations at all," he says.
Long-term stress has the effect of inhibiting the immune system against infectious diseases, but it also inhibits the body's response to vaccines.
"It's best that calves have seven to 14 days following the blizzard event for their immune system to recover from the stress before they receive initial or booster doses of vaccines. Vaccinations will be less effective in cattle that are still under the influence of cortisol due to stress," he says.
In cattle, it is generally considered that the effect of stresses on the body are additive. Any sort of transportation, processing, or weaning will add to the stresses already encountered by cows and calves going through the blizzard, or faced with moving through snowbanks or muddy lots.
SDSU Extension Cow-Calf Field Specialist Warren Rusche suggests that, if at all possible, ranchers should consider delaying marketing until the calves have had time to recover from the added stress load.
"Feedlots or backgrounders who purchase calves who have undergone these conditions should do all they can to minimize stress and provide as much T-L-C as possible. Feeders should consult with their veterinarian concerning timing of arrival vaccinations and possible preventative strategies," he says.