A path model of factors influencing morbidity and mortality in Ontario feedlot calves.

The principles of path analysis and causal modelling are discussed. Path analysis was applied to three data sets to assess the relationship between group characteristics (number per group and "mixing" subgroups of cattle, feeding-management of the group and processing factors (vaccination and prophylactic antimicrobials) and subsequent morbidity and mortality in feedlot cattle. The major findings agree with previously reported results but the timing and pathways of the effects are elaborated. In general, morbidity in week 1 was correlated with morbidity in week 2, which was correlated with morbidity in weeks 3-5. The same was generally true for mortality. In general, morbidity was not strongly correlated with mortality. Lots (unmixed groups) did not arrive in better condition, but experienced fewer subsequent health problems than mixed groups. (Silage-fed lots appeared to do poorly, however this was apparently due to the positive association between lots and vaccination, the latter being detrimental to mortality rates.) The more cattle per group, the greater the health problems in weeks 3-5 postarrival. Prophylactic antimicrobials in the water supply on arrival lead to increased health problems in the three to five week postarrival period. Antibiotic containing starter rations had a beneficial effect on health status in this period. This effect appeared to be partly due to delaying making silage the major ration component in silage-fed cattle receiving antimicrobial containing starter rations. Vaccination against respiratory disease in either of the first two weeks postarrival had detrimental direct and indirect effects on subsequent health status. Vaccination during weeks 3-5 postarrival was not significantly related to health status in that period.