EFFECT OF PRETRANSIT MIXING ON FATAL FIBRINOUS PNEUMONIA IN CALVES

A retrospective, epidemiologic study was performed to quantify the mix ing of calves from various sources at auction markets, and to determin e whether mixing at the markets and the risk of fatal fibrinous pneumo nia (FFP) at the feedlot were associated. In this study, 32,646 spring -born steer calves that entered a single large feedlot during the fall seasons between 1985 and 1988 were traced back to their originating a uction market, and sales tickets were used to measure the number of fa rm sources that contributed to each truckload of calves. Individual co w/calf producers conrributed a median of only 2 calves/truckload arriv ing at the feedlot in this study. An average truckload of 60 steers co mprised calves from as many as 20 to 30 farms. The degree of mixing va ried little over time and could not, therefore, be used to explain the large variations in FFP risk during different months and different ye ars of the study. However, variation in the degree of mixing of calves from various sources at the markets evidently was responsible for dif ferences in FFP risk among truckloads assembled by different buyers. W hen truckloads were grouped by buyer, FFP risk and mean number of calv es per source were negatively correlated in 1986 (r = -0.67, P = 0.099 ), and in 1987 (r = -0.90, P = 0.002). These variables also were negat ively con-elated in 1988 (r = -0.56), although the correlation was not significant. The positive linear relationship between mixing of calve s in truckloads supplied by different buyers and subsequent FFP risk s uggested that veterinarians and feedlot owners should more aggressivel y observe and treat calves from truckloads that were highly mixed. How ever, the finding that mixing was constant over time, while FFP risk v aried significantly within find between years, indicated other importa nt factors also were responsible for the variation in disease prevalen ce.