Objective—To evaluate trends in feedlot cattle mortality
ratios over time, by primary body system affected,
and by type of animal.
Design—Retrospective cohort study.
Animals—Approximately 21.8 million cattle entering
121 feedlots in the United States during 1994 through
Procedures—Yearly and monthly mortality ratios
were calculated. Numbers of deaths were modeled
by use of Poisson regression methods for repeated
measures. Relative risks of death over time and by
animal type were estimated.
Results—Averaged over time, the mortality ratio
was 12.6 deaths/1,000 cattle entering the feedlots.
The mortality ratio increased from 10.3
deaths/1,000 cattle in 1994 to 14.2 deaths/1,000
cattle in 1999, but this difference was not statistically
significant (P = 0.09). Cattle entering the feedlots
during 1999 had a significantly increased risk
(relative risk, 1.46) of dying of respiratory tract disorders,
compared with cattle that entered during
1994, and respiratory tract disorders accounted for
57.1% of all deaths. Dairy cattle had a significantly
increased risk of death of any cause, compared with
beef steers. Beef heifers had a significantly
increased risk of dying of respiratory tract disorders,
compared with beef steers.
Conclusions and Clinical Relevance—Results suggested
that although overall yearly mortality ratio did
not significantly increase during the study, the risk of
death attributable to respiratory tract disorders was
increased during most years, compared with risk of
death during 1994. The increased rates of fatal respiratory
tract disorders may also reflect increased rates
of non-fatal respiratory tract disorders, which would
be expected to have adverse production effects in
surviving animals. (J Am Vet Med Assoc 2001;219:1122–1127)