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 Unit
ed States during 1994 through 1999.
Procedures-Yearly and monthly mortality ratios were calculated. Numbers of
deaths were modeled by use of Poisson regression methods for repeated measu
res. Relative risks of death over time and by animal type were estimated.
Results-Ave raged over time, the mortality ratio was 12.6 deaths/1,000 catt
le 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 dy
ing of respiratory tract disorders, compared with cattle that entered durin
g 1994, and respiratory tract disorders accounted for 57.1% of all deaths.
Dairy cattle had a significantly increased risk of death of any cause, comp
ared with beef steers. Beef heifers had a significantly increased risk of d
ying 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 du
ring most years, compared with risk of death during 1994. The increased rat
es of fatal respiratory tract disorders may also reflect increased rates of
non-fatal respiratory tract disorders, which would be expected to have adv
erse production effects in surviving animals.