Stanton PhD Thesis final_docx - Atrium - University of Guelph

of calves with BRD60 survived to first calving and 84% (931/1105) of calves without BRD60
survived to first calving. Survival to first calving was 83% (559/676) and 79% (530/667) for
TUL and TET calves, respectively. Of the 237 calves with BRD60, 73% (64/88) of the TUL
calves survived to first calving and 62% (93/149) of the TET calves survived to first calving.
Survival to first calving was affected by BRD60 and antimicrobial treatment with a
significant interaction between antimicrobial treatment and BRD60, P < 0.03. For TET and TUL
calves, calves without BRD60 were 3.4 (2.2-5.2) and 1.7 (1.0-2.9) times more likely to survive to
first calving compared to BRD60 calves, respectively. Calves treated for BRD60 were 2.0 (95%
CI: 1.1-3.6) times more likely to survive to first calving if they had received TUL at movement
to group housing compared to TET. Antimicrobial treatment did not have an effect on the
probability of non-BRD60 calves surviving to first calving, (OR: 1.0; CI: 0.7-1.5, P = 0.80).
Survival to first calving by source farm is reported in Table 7.5. There was no interaction of farm
with the effect of BRD60 on survival.
7.4.5 Culling and mortality prior to first calving
Of the 255 heifers that did not survive to first calving, 36% (93/255) died and 64%
(162/255) were culled. The primary reason for mortality was BRD, with 47% (44/93) of all
deaths attributed this disease (Table 7.6). For the deaths attributed to BRD, 61% (27/44) were
treated for BRD in the 60 days following movement to group housing with 34% (15/44) and 66%
(29/44) of deaths due to BRD in the TUL and TET groups, respectively (P = 0.04). Poor
reproduction was the primary reason for culling of heifers (Table 7.7).
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