Calcium Dynamics of Periparturient Holsteins in Confinement and in Grazing Systems – Assessment and Mitigation Strategies
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The transition period of the dairy cow is hallmarked with rapidly changing demands and metabolic adaptations to better meet the Ca needs for parturition and lactogenesis. A successful transition period requires the coordination of tissue changes and hormonal signaling to avoid prolonged or deleterious depletion of Ca, irrespective of dairy system type. Though it is generally understood that the prevalence of Ca dysregulation in conventionally housed dairy cows is upwards of 30%, relatively little is known about risk factors or prevalence in grazing systems. Current understanding of dysregulation and imbalances, as well as mitigation strategies, continue to be refined in conventional and grazing systems. The objective of this dissertation was 3-fold: 1) investigate a combination of dietary approaches to modulating Ca dysregulation around the periparturient period, 2) explore the associations of macromineral dysregulation with acute increases of APP, pro-, and anti-inflammatory cytokines, and 3) assess the prevalence of SCH in grazing systems and their relationships with cow performance. Management of DCAD remains a key strategy in conventional systems, particularly targeting a urine pH between 5.5 and 6.0, fed concurrently with a high proportion of Ca (1.5%). This approach is difficult to achieve in high K forages, like those found in many grazing systems. Though precise measures and concentrations may vary between system types, grazing cows appear to have similar proportions of animals experiencing Ca dysregulation in the transition period. Moreover, regulation of inflammatory response seems to be associated with postpartum Ca dynamics and ability of the cow to recover to normal blood Ca concentrations.