歷年畢業論文

Negative energy balance (NEB) is a common metabolic regulating status in transition dairy cows. In severe NEB status, it leads to increased mobilization of body fat, resulting in elevated non-esterified fatty acids (NEFA) and β-hydroxybutyric acid (BHBA), which negatively affect physiological balance, health status, and productivity of dairy cows. This study investigated the effects of these lipid metabolites on immune regulation, reproductive disorder risk, and productive performance. At first, to investigate the effects of NEFA and BHBA on peripheral leukocytes, a primary immune cell culture model was introduced to examine the impacts of high levels of NEFA and BHBA at NEB status. High levels of NEFA upregulated pro-inflammatory cytokine (PIC) expression in both peripheral blood mononuclear cells (PBMC) and polymorphonuclear leukocytes (PMN), while BHBA only affected PIC expression in PBMC. In combination with LPS to simulate pathogen infection, only NEFA further enhanced LPS-induced PIC changes, identifying NEFA as the principal lipid metabolite influencing immune function. NEFA-induced oxidative stress was only observed in PBMC, which was alleviated by vitamin E pretreatment. Furthermore, vitamin E also partially inhibited NEFA-induced PIC upregulation. Secondly, the relationship between blood NEFA and BHBA concentrations and the incidence of postpartum reproductive disorders was analyzed. Elevated lipid metabolite concentrations significantly increased the risk of postpartum reproductive problems: multiparous cows with high serum NEFA of 0.45 mM above on the calving day show a 25-fold higher risk of subclinical endometritis, and primiparous cows with the serum BHBA of 0.73 mM above on postpartum day 2 had a 35-fold higher risk of anovulation. Cows with higher lipid metabolite levels have higher neutrophil-to-lymphocyte ratios (NLR), indicating increased systemic inflammation and reproductive risk. Finally, the effects of NEFA and BHBA on behaviors were assessed, and milking parameters recorded by the automatic milking system (AMS) were analyzed. Cows with higher serum levels of lipid metabolites on the calving day showed shorter eating and total feeding times, lower milking flow rates (in primiparous cows), and greater variability in milking intervals, especially with increased NEFA levels. Cows with higher NLR (1.17 above), which suggested an inflammatory status, showed reduced feeding time and milking frequency. In summary, elevated serum lipid metabolites of NEFA and BHBA during the transition period negatively impact health, behaviors, and milking performance of dairy cows and are associated with inflammation. NEFA is a better blood biomarker than BHBA for assessing these outcomes. Furthermore, control of serum NEFA may help to improve health conditions and productivity in transition dairy cows.
 
Keywords: transition period, non-esterified fatty acids, β-hydroxybutyric acid, reproduction, behavior, inflammation, automatic milking system