EFFECT OF TIME OF YEAR, WEATHER, AND THE PATTERN OF AUCTION MARKET SALES ON FATAL FIBRINOUS PNEUMONIA (SHIPPING FEVER) IN CALVES IN A LARGEFEEDLOT IN ALBERTA (1985-1988)

A total of 58 885 spring-born calves entering a large commercial feedl ot in southwestern Alberta were studied to examine the associations be tween shipping fever mortality and the pattern of calf sales at the au ction markets, time of year, and weather. The observational study foll owed calves purchased from 42 auction markets in the 4 western provinc es 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 enteri ng the feedlot in November had a risk of fatal shipping fever 2 to 8 t imes greater than calves entering in September or December. The patter n was the same for all 4 years, with maximum risk occurring 2 to 4 wee ks after the peak time for calf sales at the markets. A number of fact ors could have contributed to this pattern, including changes in trans port truck availability, changes in the density of calves at the marke ts, changes in population dynamics at the feedlot that affected feedlo t crew efficiency, and weather. The finding that the risk of fatal shi pping fever appears to increase significantly as the feedlot fills wit h calves in the fall deserves the attention of feedlot owners, so they can design their treatment strategies appropriately, and of researche rs, who may gain useful knowledge about the natural history of the dis ease by investigating why this change in risk occurs.