Stanton PhD Thesis final_docx - Atrium - University of Guelph

months of age. The lower growth rate indicates that calves recover very slowly from BRD, and
that BRD has potentially altered the calves’ physiology or behavior either through decreased
feed efficiency or decreased feed intake. The long-term effects of BRD were further
demonstrated by the lower probability that calves with BRD would survive to first calving, the
greater age at first calving and the higher risk of some level of dystocia at first calving, relative
to calves that did not experience BRD during the 60 days following movement to group housing.
The effect of BRD on milk production was less clear due to a likely healthy worker bias resulting
from the high rate of removal of BRD heifers prior to calving. To avoid this bias, a different
approach may be required in that the animal’s genetic potential for milk production should be
accounted for in the model to determine if BRD decreases milk production. This evaluation
would require a larger sample size than was available in this study since it would require many
daughters sharing the same sire.
The results of these three thesis objectives have demonstrated that a multi-disciplinary
approach to improving management of dairy calf health and the identification of long-term
impacts of disease are beneficial. Future research should continue to address the issues of early
disease identification, risk management and animal health in order to improve the productivity
and welfare of dairy calves.
8.2 FUTURE RESEARCH
Although several management procedures that are associated with reducing the risk of
dairy calf disease, and some behaviors associated with poor growth were investigated in this
thesis, these findings also illustrated many other areas of investigation that need to be considered.
203