Effect of time of year, weather, and the pattern of auction market sales on fatal fibrinous pneumonia (shipping fever) in calves in a large feedlot in Alberta (1985-1988).

A total of 58,885 spring-born calves entering a large commercial feedlot in southwestern Alberta were studied to examine the associations between shipping fever mortality and the pattern of calf sales at the auction markets, time of year, and weather. The observational study followed calves purchased from 42 auction markets in the 4 western provinces between September 1 and December 31 in each of the years from 1985 to 1988. Calf sales at the auction markets consistently peaked during the last week of October and the first week of November. Calves entering the feedlot in November had a risk of fatal shipping fever 2 to 8 times greater than calves entering in September or December. The pattern was the same for all 4 years, with maximum risk occurring 2 to 4 weeks after the peak time for calf sales at the markets. A number of factors could have contributed to this pattern, including changes in transport truck availability, changes in the density of calves at the markets, changes in population dynamics at the feedlot that affected feedlot crew efficiency, and weather. The finding that the risk of fatal shipping fever appears to increase significantly as the feedlot fills with calves in the fall deserves the attention of feedlot owners, so they can design their treatment strategies appropriately, and of researchers, who may gain useful knowledge about the natural history of the disease by investigating why this change in risk occurs.