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dc.contributor.authorOspina, Paulaen_US
dc.description.abstractThe 3 weeks pre-partum to 3 weeks post-partum is a challenging time for dairy cows because of both environmental and biological changes taking place in preparation for parturition and lactation. At the animal level, excessive negative energy balance (NEB) can increase the risk of developing displaced abomasa, clinical ketosis, metritis, and/or retained placenta and can negatively affect reproduction and milk production. Non-esterified fatty acids (NEFA) and betahydroxybutyrate (BHBA) are measurable blood metabolites used to estimate the level of NEB. The objectives of herein were to: 1) identify critical concentrations of NEFA and BHBA above which the development of diseases were more likely; 2) describe statistical methods for best evaluating these effects as risk ratios; 3) identify the NEFA and BHBA critical concentrations associated with decreased reproductive performance and milk production; 4) evaluate the herd alarm level, i.e., the association between the proportion of animals sampled that had NEFA and BHBA concentrations above the thresholds and herd-level disease incidence, reproductive, and milk production outcomes; 5) compare the results of pooling samples versus evaluating individual animals that were above a herd alarm level; and 6) evaluate the herd-level sensitivity, specificity, and herd predictive value positive and negative when using individual samples to estimate herd-level risk. Animals with elevated concentrations of pre- and post-partum NEFA (0.3 and 0.7 mEq/L, respectively) and post-partum BHBA (12 mg/dL) were more likely to develop diseases; less likely to get pregnant. The effects of elevated metabolites on milk production at the individual animal level were different between cows and heifers, cows produced less milk while heifers produced more. However, when animals were evaluated at the herd level (i.e., when more than 15-20% of the animals sampled had metabolite concentrations above the critical thresholds) elevated NEFA and BHBA were associated with decreased milk in all groups. When evaluating NEB at the herd-level, pooled samples are not recommended because they have low sensitivity. It is recommended to sample 15 animals to maximize HPVand 20 to maximize HPV+. The information acquired from this research will help improve transition cow monitoring and management strategies.en_US
dc.titleThe Association Between Non-Esterified Fatty Acids And Beta-Hydroxybutyrate During The Transition Period In Holstein Dairy Cows And Negative Downstream Outcomes - Disease Incidence, Milk Production And Reproductionen_US
dc.typedissertation or thesisen_US Science Universityen_US of Philosophy D., Animal Science
dc.contributor.chairNydam, Daryl Vanen_US
dc.contributor.committeeMemberStokol, Tracyen_US
dc.contributor.committeeMemberOverton, Thomas Ren_US
dc.contributor.committeeMemberGuard III, Charles Len_US

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