Invited review: Ketone biology-The shifting paradigm of ketones and ketosis in the dairy cow.

Ketosis is currently regarded as a major metabolic disorder of dairy cows, reflective of the animal's efforts to adapt to energy deficit while transitioning into lactation. Currently viewed as a pathology by some, ketosis is associatively implicated in milk production losses and peripartal health complications that increase the risk of early removal of cows from the herd, thus carrying economic losses for dairy farmers and jeopardizing the sustainability of the dairy industry. Despite decades of intense research in the mitigation of ketosis and its sequelae, our ability to lessen its purported effects remains limited. Moreover, the association of ketosis to reduced milk production and peripartal disease is often erratic and likely mired by concurrent potential confounders. In this review, we discuss the potential reasons for these apparent paradoxes in the light of currently available evidence, with a focus on the limitations of observational research and the necessary steps to unambiguously identify the effects of ketosis on cow health and performance via controlled randomized experimentation. A nuanced perspective is proposed that considers the dissociation of ketosis-as a disease-from healthy hyperketonemia. Furthermore, in consideration of a growing body of evidence that highlights positive roles of ketones in the mitigation of metabolic dysfunction and chronic diseases, we consider the hypothetical functions of ketones as health-promoting metabolites and ponder on their potential usefulness to enhance dairy cow health and productivity.

Intravenous trimethylamine N-oxide infusion does not modify circulating markers of liver health, glucose tolerance, and milk production in early-lactation cows.

In rodents and humans, the gut bacteria-derived metabolite trimethylamine N-oxide (TMAO) has been implicated in the progression of cardiovascular disease, chronic kidney disease, fatty liver, and insulin resistance; however, the effects of TMAO on dairy cattle health and milk production have not been defined. We aimed to determine whether intravenous TMAO infusion modifies measures of liver health, glucose tolerance, and milk production in early-lactation cows. Eight early-lactation Holstein cows (30.4 ± 6.41 d in milk; 2.88 ± 0.83 lactations) were enrolled in a study with a replicated 4 × 4 Latin square design. Cows were intravenously infused TMAO at 0 (control), 20, 40, or 60 g/d for 6 d. Washout periods lasted 9 d. Intravenous glucose tolerance tests (GTT) occurred on d 5. Blood was collected daily. Milk was collected on d -1, 0, 5, and 6. Urine was collected on d -1 and 6. Circulating metabolites, milk components, and TMAO concentrations in milk, urine, and plasma were quantified. Data were analyzed using a mixed model that included the fixed effects of treatment. Concentrations of TMAO in plasma, milk, and urine increased linearly with increasing dose. Dry matter intake and milk production were not modified by treatment. Daily plasma triacylglycerol, fatty acid (FA), and glucose concentrations were not modified. Serum albumin, total protein, globulin, total bilirubin, direct bilirubin, aspartate aminotransferase, γ-glutamyl transferase, and glutamate dehydrogenase concentrations were also not modified by treatment. Serum GTT glucose, FA, and insulin concentrations were not modified by treatment. Plasma total, reduced, and oxidized glutathione concentrations were also not modified by treatment. We conclude that a 6-d intravenous infusion of TMAO does not influence measures of liver health, glucose tolerance, or milk production in early-lactation dairy cows.

Flaxseed Oil or n-7 Fatty Acid-Enhanced Fish Oil Supplementation Alters Fatty Acid Composition, Plasma Insulin and Serum Ceramide Concentrations, and Gene Expression in Lambs.

The objective of this study was to examine the effects of flaxseed (FLAX) oil or 16-carbon n-7 fatty acid -enhanced fish oil (Provinal; POA) supplementation on serum, liver and skeletal muscle fatty acid concentrations, serum ceramide and plasma insulin concentrations, and gene expression. Lambs [n = 18; 42 ± 5.6 kg body weight (BW); 7 months] were individually fed one of the three treatments: (1) control (CON), no oil supplement, (2) FLAX; at 0.1% of BW, or (3) POA at 0.1% of BW for 60 days. Daily feed intake and weight gain were decreased by 21% and 34%, respectively, for POA than FLAX. Liver and skeletal muscle concentrations of palmitoleic acid were greater by 396% and 87%, respectively, for POA than FLAX; whereas, liver and skeletal muscle α-linolenic acid concentrations were greater by 199% and 118%, respectively, for FLAX. Supplementation with POA also had greater serum and tissue concentrations of eicosapentaenoic and docosahexaenoic acids. Serum glucose and plasma insulin concentrations were elevated with FLAX supplementation at the end of the study. Supplementation with POA altered serum ceramide concentrations compared to CON or FLAX. Oil supplementation, both FLAX and POA, downregulated expression of unesterified fatty acid receptors (FFAR) 1 and FFAR4 in the liver; however, oil supplementation upregulated expression of FFAR1 in muscle. Interleukin-6 (IL6) and tumor necrosis factor-α (TNFA) expression were downregulated with oil supplementation in the liver; however, FLAX upregulated TNFA in muscle. These results show that oil supplementation can enhance uptake and deposition of unique fatty acids that alter ceramide concentrations and gene expression in tissues.

Intravenous Triacylglycerol Infusion Promotes Ceramide Accumulation and Hepatic Steatosis in Dairy Cows.

Background: Increased plasma free fatty acids (FFAs) impair insulin sensitivity in dairy cows via unknown mechanisms. In nonruminants, saturated FFAs upregulate the hepatic synthesis and secretion of ceramide, which inhibits insulin action. Objective: We aimed to determine whether an increase in plasma FFAs promotes hepatic and plasma ceramide accumulation in dairy cows. Methods: Six nonpregnant, nonlactating Holstein cows were used in a study with a crossover design and treatments consisting of intravenous infusion of either saline (control) or triacylglycerol emulsion (TG; 20 g/h) for 16 h. The feeding level was set at 120% of energy requirements. Blood was collected at regular intervals and liver was biopsied at 16 h. Ceramides, monohexosylceramides (Glc/Gal-Cer), lactosylceramides (LacCer), and sphingomyelins (SMs) in plasma and liver were profiled. Hepatic expression of ceramide synthases was determined. Data were analyzed with the use of mixed models, regressions, and Spearman rank correlations. Results: After 16 h of infusion, plasma FFA concentrations were >5-fold and liver triacylglycerol concentrations were 4-fold greater in TG cows, relative to control. Plasma total and very long-chain ceramide (e.g., C24:0-ceramide) concentrations increased ∼4-fold in TG over control by hour 16 of infusion, while C16:0-ceramide were not modified by TG. Infusion of TG increased plasma Glc/Gal-Cer (e.g., C16:0-Glc/Gal-Cer, 4-fold by hour 16) relative to control, but did not alter LacCer or SM concentrations. Hepatic ceramide concentrations increased with TG relative to control (e.g., C24:0-ceramide by 1.7-fold). Hepatic expression of ceramide synthase 2 was 60% greater after TG infusion compared with the control. Circulating ceramides were related to circulating FFA and hepatic triacylglycerol concentrations (e.g., C24:0-ceramide, ρ = 0.73 and 0.80, respectively; P < 0.001). Conclusion: Hepatic ceramide synthesis is associated with elevations in circulating FFAs and hepatic triacylglycerol during the induction of hyperlipidemia in dairy cows. This work supports the emerging evidence for the role of ceramide during hepatic steatosis and insulin antagonism in cows.

Temporal changes in sphingolipids and systemic insulin sensitivity during the transition from gestation to lactation.

Reduced insulin action develops naturally during the peripartum to ensure maternal nutrient delivery to the fetus and neonate. However, increased insulin resistance can facilitate excessive lipolysis which in turn promotes metabolic disease in overweight dairy cattle. Increased fatty acid availability favors the accumulation of the sphingolipid ceramide and is implicated in the pathogenesis of insulin resistance, however, the relationship between sphingolipid metabolism and insulin resistance during the peripartum remains largely unknown. Our objectives were to characterize temporal responses in plasma and tissue sphingolipids in lean and overweight peripartal cows and to establish the relationships between sphingolipid supply and lipolysis, hepatic lipid deposition, and systemic insulin action. Twenty-one multiparous lean and overweight Holstein cows were enrolled in a longitudinal study spanning the transition from gestation to lactation (d -21 to 21, relative to parturition). Plasma, liver, and skeletal muscle samples were obtained, and sphingolipids were profiled using LC/MS/MS. Insulin sensitivity was assessed utilizing intravenous insulin and glucose challenges. Our results demonstrated the following: first, insulin resistance develops postpartum concurrently with increased lipolysis and hepatic lipid accumulation; second, ceramides and glycosylated ceramides accumulate during the transition from gestation to lactation and are further elevated in overweight cows; third, ceramide accrual is associated with lipolysis and liver lipid accumulation, and C16:0- and C24:0-ceramide are inversely associated with systemic insulin sensitivity postpartum; fourth, plasma sphingomyelin, a potential source of ceramides reaches a nadir at parturition and is closely associated with feed intake; fifth, select sphingomyelins are lower in the plasma of overweight cows during the peripartal period. Our results demonstrate that dynamic changes occur in peripartal sphingolipids that are influenced by adiposity, and are associated with the onset of peripartal insulin resistance. These observations are in agreement with a putative potential role for sphingolipids in facilitating the physiological adaptations of peripartum.