While we generally think of bovine respiratory disease (BRD) as a problem associated with shipped stocker and feeder calves, about 20 percent of ranches experience some incidence BRD in pre-weaned calves on their home pastures. During the recent American Association of Bovine Practitioners (AABP) conference in New Orleans, Mississippi State University veterinarians Dave Smith, DVM, PhD, DACVPM, and Amelia Woolums, DVM, MVSc, PhD, ACVIM, ACVM, outlined research into risk factors associated with BRD in pre-weaned calves.
BRD is the leading cause of death in calves three weeks of age or older, Wollums says. Smith adds that economic data indicate that losses due to BRD on ranches add up to around $200 to $300 million in the U.S. each year, or about $7 to $ 10 per cow overall and $35 to 50 per cow in affected herds.
Data from multiple studies show that BRD tends to break out in calves at two times. Sporadic outbreaks occur in young calves, typically at around 20 to 30 days, with the sickness likely related to failure of passive transfer from the dam. Larger outbreaks occur later, typically peaking at around 120 days, during the gap between the decline in passive immunity and full development of the active immune system, leading to a loss of herd immunity.
In a large survey of 2,600 US cow-calf producers in three Eastern and three Plains states, researchers found detection of BRD in calves was significantly associated with large herd size, detection of BRD in cows, and diarrhea in calves. Calving season length was associated with BRD in calves in Plains states but not Eastern states. Incidence of BRD treatment was positively associated with calving during the winter, introduction of calves from an outside source, offering supplemental feed to calves, and use of an estrous cycle synchronization program for cows.
Other studies have shown associations between several factors and BRD incidence, including:
· Year of birth – Incidence can vary widely year-to-year on the same ranch.
· Location of calf on the operation – Some areas could provide more opportunity for exposure to pathogens.
· Sex of the calf – Male calves appear more likely to experience BRD than female calves.
· Dam age – Calves born to heifer dams seem more likely to experience BRD, and experience it earlier in life, than those born to older cows.
In another large survey of producers, at least 50 percent of respondents selected “weather”, “inadequate colostrum consumption”, “introducing new cattle”, “failure to give nursing calves BRD vaccines”, “failure to give cows BRD vaccines”, “calf diarrhea in the herd”, “vitamin/mineral deficiency for cows/calves”, “protein/energy deficiency for cows/calves”, “BVDV PI cattle in the herd”, and “calving cows and/or heifers in confinement” as contributing to nursing calf BRD.