THE STUDY OF ENERGY METABOLISM IN THE PERIPARTURIENT DAIRY COW: INVESTIGATING THE ROLE OF KETONES AND NAD+

Abstract

Dairy cows typically experience increased energy demands during the transition from gestation to lactation, and a myriad of metabolic adaptations are set in place to facilitate this transition. This thesis integrates findings from two experiments exploring energy metabolism during this critical phase. In the first experiment, the effects of hyperketonemia on dairy cow health and productivity were investigated. Eight Holstein cows (19.62 ± 5.44 days postpartum) were intravenously infused with either Na-BHB (KET) or NaCl (CON) for 48 hours. The study aimed to assess the impact of elevated beta-hydroxybutyrate (BHB) levels on blood biomarkers and immune response. Despite no significant differences in dry matter intake or overall milk yield, KET cows exhibited lower milk yield post-immune challenge (LPS bolus) and higher plasma NEFA levels. While plasma glucose concentrations remained unchanged, but BHB concentrations were significantly higher in the KET group (P < 0.001). The second experiment focused on the role of Nicotinamide Adenine Dinucleotide (NAD) coenzymes in energy metabolism during the transition from gestation to lactation. Twenty-six peripartal dairy cows were enrolled in an observational study to examine the NAD metabolome in liver, blood, and milk. Liver biopsies were performed 21 days before and 7 days after parturition, and blood samples were collected weekly. The study hypothesized that hepatic NAD levels deplete while blood and milk NAD pools increase postpartum, with a possible influence of residual feed intake (RFI). Measurements of plasma glucose, free fatty acids, BHB, and insulin, along with comprehensive NAD metabolome profiling using HPLC coupled to mass spectrometry, aimed to elucidate the relationship between NAD metabolism, metabolic biomarkers, and production performance. After calving, animals showed decreased glucose and insulin levels, and increased NEFA and BHB levels, with no significant group differences (P = 0.53). Oxidative stress markers (protein carbonyl, 8-OHdG) and total antioxidant capacity were measured on plasma. The DNA and protein oxidative stress markers remained unchanged relative to parturition, but the Low-RFI group tended to display higher antioxidant capacity (P = 0.08). NAD metabolites increased, and NAD precursor concentrations decreased in the liver. Nicotinamide Mononucleotide was higher in the High-RFI group (P = 0.04) and tended to decrease post-calving (P = 0.06). The liver NAD metabolome remained stable (P = 0.83). Both studies underscore the complexity of energy metabolism during the peripartum period in dairy cows. Collectively, our findings expand our understanding of novel aspects of energy metabolism, with potential implications for health, productivity, and disease resilience in dairy cows. Further research is essential to fully understand these mechanisms and improve management strategies for dairy cows during this critical period.