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Simple Summary: The effect of Scalarpin 2 (STC2) on chicken hepatic lipid metabolism is still unknown. In this study, we found that genetic variation rs9949205 occurring in the STC2 was significantly associated with chicken body weight at different weeks and carcass traits. The inhibitory effect of STC2 on lipid synthesis in LMH cells was observed, and its expression level in muscle showed a significant association with 176 lipids, predominantly enriched in essential omega-3 and omega-6 fatty acids. The evidence suggests that STC2 involved growth and development, as well as lipid metabolism in chickens. Stanniocalcin 2 (STC2) is a secreted glycoprotein involved in multiple biological processes. To systemically study the biological role of STC2 in chickens, phylogenetic tree analysis and conservation analysis were conducted. Association analysis between variations in the STC2 gene and the economic traits of Gushi-Anka F2 was conducted. The tissue expression patterns of STC2 expression in different chicken tissues and liver at different stages were detected. The biological role of STC2 in chicken liver was investigated through overexpression and interfering methods in the LMH cell line. Correlation analyses between STC2 expression and lipid components were conducted. (1) The phylogenetic tree displayed that chicken STC2 is most closely related with Japanese quail and most distantly related with Xenopus tropicalis. STC2 has the same identical conserved motifs as other species. (2) rs9949205 (T > C) found in STC2 intron was highly significantly correlated with chicken body weight at 0, 2, 4, 6, 8, 10 and 12 weeks (p < 0.01). Extremely significant correlations of rs9949205 with semi-evisceration weight (SEW), evisceration weight (EW), breast muscle weight (BMW), leg muscle weight (LMW), liver weight and abdominal fat weight (AFW) were revealed (p < 0.01). Significant associations between rs9949205 and abdominal fat percentage, liver weight rate, breast muscle weight rate and leg muscle weight rate were also found (p < 0.05). Individuals with TT or TC genotypes had significantly lower abdominal fat percentage and liver weight rate compared to those with the CC genotype, while their body weight and other carcass traits were higher. (3) STC2 showed a high expression level in chicken liver tissue, which significantly increased with the progression of age (p < 0.05). STC2 was observed to inhibit the content of lipid droplets, triglycerides (TG) and cholesterol (TC), as well the expression level of genes related to lipid metabolism in LMH cells. (4) Correlation analysis showed that the STC2 gene was significantly correlated with 176 lipids in the breast muscle (p < 0.05) and mainly enriched in omega-3 and omega-6 unsaturated fatty acids. In conclusion, the STC2 gene in chicken might potentially play a crucial role in chicken growth and development, as well as liver lipid metabolism and muscle lipid deposition. This study provides a scientific foundation for further investigation into the regulatory mechanism of the STC2 gene on lipid metabolism and deposition in chicken liver. [ABSTRACT FROM AUTHOR]

Simple Summary: The production of artificially farmed bullfrogs in China is limited by the low metamorphosis rate of tadpoles. This study investigated the effects of different doses (0 g/kg, 1.5 g/kg, 3 g/kg, 4.5 g/kg, and 6 g/kg) of thyroid powder added to the diets on the metamorphosis and growth of bullfrog tadpoles. The results showed that 4.5 g/kg of thyroid powder could significantly increase the metamorphosis rate and weight gain rate of tadpoles, while adding 6 g/kg of thyroid powder could increase the average weight of tadpoles during metamorphosis. In addition, both doses of thyroid powder could promote the fat breakdown metabolism of tadpoles and alter the intestinal microbiota composition (increasing the abundance of beneficial bacteria, especially Akkermansia). In summary, appropriate doses of thyroid powder could promote the metamorphosis and growth of tadpoles, and might be used to solve the problem of the low metamorphosis rate of bullfrogs. A low metamorphosis rate of amphibian larvae, commonly known as tadpoles, limits the farming production of bullfrogs (Lithobates catesbeiana). This study aimed to examine the effects of processed thyroid powder as a feed additive on tadpole metamorphosis, lipid metabolism, and gut microbiota. Five groups of tadpoles were fed with diets containing 0 g/kg (TH0), 1.5 g/kg (TH1.5), 3 g/kg (TH3), 4.5 g/kg (TH4.5), and 6 g/kg (TH6) thyroid powder for 70 days. The results showed that TH increased the average weight of tadpoles during metamorphosis, with the TH6 group having the highest values. The TH4.5 group had the highest metamorphosis rate (p < 0.05). Biochemical tests and Oil Red O staining showed that the lipid (triglyceride) content in the liver decreased after TH supplementation, especially at doses higher than 1.5 g/kg. RT-qPCR revealed that TH at doses higher than 4.5 g/kg significantly up-regulated the transcriptional expression of the pparα, accb, fas, fadd6, acadl, and lcat genes, which are related to lipid metabolism (p < 0.05). These results showed that TH seems to simultaneously promote the synthesis and decomposition of lipid and fatty acids, but ultimately show a decrease in lipids. As for the gut microbiota, it is noteworthy that Verrucomicrobia increased significantly in the TH4.5 and TH6 groups, and the Akkermansia (classified as Verrucomicrobia) was the corresponding genus, which is related to lipid metabolism. Specifically, the metabolic pathways of the gut microbiota were mainly enriched in metabolic-related functions (such as lipid metabolism), and there were significant differences in metabolic and immune pathways between the TH4.5 and TH0 groups (p < 0.05). In summary, TH may enhance lipid metabolism by modulating the gut microbiota (especially Akkermansia), thereby promoting the growth of tadpoles. Consequently, a supplementation of 4.5 g/kg or 6 g/kg of TH is recommended for promoting the metamorphosis and growth of tadpoles. [ABSTRACT FROM AUTHOR]

Simple Summary: In this study, we investigated the effects of adding soybean oligosaccharides (SBOS) to growing–finishing pig diets on growth performance, carcass traits, meat quality, and fat deposition. SBOS are considered to be one of the causes of diarrhea in piglets. However, their impact on growing and fattening pigs has not been reported. The results of this study showed that adding 0.8% SBOS to the diet of growing–finishing pigs can increase the average daily weight gain. Hindgut fermentation of SBOS, which alters the composition of short-chain fatty acids, was the mechanism behind the reduction in fat deposition in growing–finishing pigs. One hundred and twenty-eight boars and gilts of the Duroc × Landrace × Yorkshire variety with an initial body weight (BW) of 52.49 ± 0.48 kg were used in a randomized complete block design for a 63-day experiment. The four treatment groups were: control diet (CON), CON + 0.2% soybean oligosaccharides (SBOS), CON + 0.4% SBOS, and CON + 0.8% SBOS. The results showed that the average daily weight gain (ADG) was significantly higher in the 0.8% SBOS group than in the CON group on days 0–63 (p < 0.05). Compared with the CON group, adding 0.8% SBOS to the diet significantly increased the carcass weight, dressing percentage, and carcass lean percentage, but decreased the average backfat depth of growing–finishing pigs (p < 0.05). Adding different concentrations (0.2%, 0.4%, and 0.8%) of SBOS to the diet can significantly increase the concentrations of acetate, propionate, and butyrate in feces (p < 0.05). The activities of malic enzyme and fatty acid synthase in the 0.8% group were significantly lower than those in the 0.2% and CON groups (p < 0.05). In summary, 0.8% SBOS supplementation to growing–finishing pigs' diets can reduce lipid deposition and increase ADG. [ABSTRACT FROM AUTHOR]

Simple Summary: Palm oil is currently the most widely used fat source for food production, but palm oil production is associated with severe environmental problems. Insect fat from Hermetia illucens larvae might be a suitable alternative fat source, because its production is more sustainable and less harmful to the environment. Thus, the present study investigated the effect of Hermetia fat, as compared to palm oil and soybean oil, on the hepatic lipid metabolism and the plasma metabolome of healthy rats, which were fed diets containing either soybean oil, palm oil, or Hermetia fat for 4 weeks. Growth performance, liver and plasma lipid concentrations, and the expression of hepatic genes involved in lipid metabolism and inflammation did not differ between groups. Plasma metabolomics revealed a clear separation of the plasma metabolomes of the soybean oil group and the other two groups, but not of those of the palm oil and the Hermetia fat group. The present study shows that Hermetia fat exerts no adverse effects on lipid metabolism and inflammatory gene expression in the liver of healthy rats compared to palm oil or soybean oil. Thus, the present findings indicate that Hermetia fat is a safe alternative fat source to palm oil for food production. Palm oil (PO) is currently the most widely used fat source for food production, but insect fat from Hermetia illucens larvae (HF) might be a suitable alternative fat source, because its production is less harmful to the environment. The present study investigated the effect of HF, as compared to PO and soybean oil (SO), on the hepatic lipid metabolism and the plasma metabolome of healthy rats, which were randomly assigned to three groups (n = 10 rats/group), and fed three different semi-synthetic diets containing either SO, PO, or HF as the main fat source for 4 weeks. Feed intake, body weight gain, liver and plasma lipid concentrations, and the hepatic mRNA levels of genes involved in lipid metabolism and inflammation did not differ between groups. Targeted plasma metabolomics revealed 294 out of 630 metabolites analyzed to be different between groups. Principal component analysis showed a clear separation of the plasma metabolomes of the SO group and the other two groups, but no separation of those of the PO and the HF groups. The present study shows that HF exerts no adverse metabolic effects in healthy rats, compared to PO or SO, indicating that HF is a safe alternative fat source to PO for food production. [ABSTRACT FROM AUTHOR]

Simple Summary: Pharmaceuticals used to treat abnormal cholesterol levels in the blood are known as lipid regulators (fibrates and statins), and their use is in constant growth. Treatment plants are usually unable to efficiently remove these compounds from wastewater, where their degradation rate is considerably slow, making them an emerging concern for aquatic systems. The present work reviews previously published research concerning the effects of these pharmaceuticals on several finfish species worldwide. Results suggest that both short- and long-term exposure to lipid regulators may have negative effects on fish health, affecting their metabolism and immune system and causing reproductive and developmental disorders. However, the information on these compounds in the available literature is still limited, and additional research is needed to fully understand the threat that their presence in aquatic systems may pose to the production of finfish by the aquaculture industry. The most documented fibrates are gemfibrozil, clofibrate and bezafibrate, while for statins, the majority of the published literature focuses on atorvastatin and simvastatin. The present work reviews previously published research concerning the effects of these hypocholesterolaemic pharmaceuticals on fish, with a particular focus on commercially important species, commonly produced by the European aquaculture industry, specifically in recirculated aquaculture systems (RAS). Overall, results suggest that both acute and chronic exposures to lipid-lowering compounds may have adverse effects on fish, disrupting their capacity to excrete exogenous substances, as well as both lipid metabolism and homeostasis, causing severe ontogenetic and endocrinological abnormalities, leading to hampered reproductive success (e.g., gametogenesis, fecundity), and skeletal or muscular malformations, having serious repercussions on fish health and welfare. Nonetheless, the available literature focusing on the effects of statins or fibrates on commonly farmed fish is still limited, and further research is required to understand the implications of this matter on aquaculture production, global food security and, ultimately, human health. [ABSTRACT FROM AUTHOR]

Simple Summary: Tea tree oil (TTO) plays an important role in regulating lipid metabolism and has anti-inflammatory properties. However, the effects of TTO in postpartum dairy cows remain to be investigated. The experimental results show that dry matter intake (DMI) tended to increase (p = 0.07) in the 0.01% TTO group relative to that in the control group. Remarkably, the levels of globulin (GLO) and immunoglobulin G (IgG) were elevated (p < 0.05) in the TMR diet supplemented with 0.02% TTO compared to those in the control. In addition, 0.02% TTO increased (p < 0.05) serum glucose levels. In conclusion, these results suggest that TTO could improve lipid metabolism and enhance immunity in postpartum dairy cows. TTO may be a novel resolution strategy for body condition recovery and milk performance improvement. Tea tree oil (TTO) plays an important role in regulating lipid metabolism and has anti-inflammatory properties. In postpartum dairy cows, dry matter intake (DMI) is dramatically decreased, resulting in lipid metabolism disorder and the systemic pro-inflammatory response. However, the effects of TTO on glucolipid metabolism and immunity in postpartum dairy cows remain uninvestigated. Therefore, this study aimed to evaluate the effects of TTO on production performance, serum biochemical indicators, and immunity in postpartum dairy cows. Our results demonstrate that DMI tended to increase (p = 0.07) in the total mixed ration (TMR) diets supplemented with 0.01% TTO/dry matter (DM) basis relative to that in the control group. The 4% fat-corrected milk (FCM) content in the 0.01% and 0.02% TTO groups showed an increase (p = 0.09) compared with that in the control. Remarkably, the levels of globulin (GLO) and immunoglobulin G (IgG) were elevated (p < 0.05) in the TMR diet supplemented with 0.02% TTO compared to those in the control group. The TTO caused no profound changes in cholesterol (CHO), triglyceride (TG), high-density lipoprotein (HDL), or low-density lipoprotein (LDL). Notably, 0.02% TTO increased (p < 0.05) the serum glucose concentration relative to that in the control group. In conclusion, our results demonstrate that TTO could improve glucolipid metabolism and enhance immunity in postpartum dairy cows. It may be a novel resolution strategy for body condition recovery and the improvement of milk performance. [ABSTRACT FROM AUTHOR]

Simple Summary: Several features of periparturient mares' physiology have been investigated; however, the possible linkage between HPA axis, leptin, and lipid metabolism in periparturient mares has received little attention. Therefore, the present study aimed to investigate the dynamic changes of adrenocorticotrophic hormone, cortisol, leptin, UCP1, lipids and liproteins levels in mares during late pregnancy and the postpartum period. The findings obtained in the current survey showed a dynamic modulation of studied parameters, namely the response to hormonal and metabolic adaptations, occurring during the peripartum period in mares. This study suggests an interaction of the HPA axis with lipid metabolism in mares, probably to deal with the metabolic load occurring during pregnancy and with lactation energy supplies. This study aimed to investigate the dynamic change of adrenocorticotrophic hormone (ACTH), cortisol, leptin, mitochondrial uncoupling protein 1 (UCP1), lipids and lipoproteins in mares during late pregnancy and the postpartum period. A total of 20 mares (10 pregnant mares, monitored from 14 ± 2 days before expected foaling until 14 days after foaling, Group A; 10 non-pregnant and non-lactating mares, Group B) were enrolled in the study. Body Condition Score (BCS) and body weight (BW) values were recorded from each animal. In Group A, blood samples were collected on days 14 ± 2 and 7 ± 2 before foaling (T−14; T−7), and on days 7 and 14 after foaling (T+7; T+14). From mares of Group B, blood samples were collected at the beginning of the study. The levels of ACTH, cortisol, leptin, UCP1, non-esterified fatty acids (NEFAs), total cholesterol, high-density lipoproteins (HDLs), low-density lipoproteins (LDLs), triglycerides and very-low-density lipoproteins (VLDLs) were investigated. While BCS showed no statistical change throughout the monitoring period (p > 0.05), all the other studied parameters displayed statistically significant variations in Group A over the peripartum period (p < 0.0001). A significant effect of pregnancy was found on all studied parameters (p < 0.001). The ACTH and cortisol levels measured in mares belonged to Group A showed a significant positive correlation with the values of leptin, LDLs, triglycerides and VLDLs, whereas they were negatively correlated with the serum UCP1 and NEFAs values. Together, the findings gathered in this study highlight a dynamic change of serum leptin, UCP1 and lipid parameters in peripartum mares and suggest an interaction of the HPA axis with lipid metabolism and mobilization in mares during the peripartum period in order to deal with metabolic and energy demand and maintain energy homeostasis. [ABSTRACT FROM AUTHOR]

Simple Summary: Fat differentiation affects lipid deposition and is a complex metabolic process. It has been previously reported that multiple transcription factors regulate adipocyte formation. With the in-depth study of epigenetics, in recent years it has been reported that long noncoding RNA (lncRNA) can effectively affect the formation of lipid droplets and thus regulate fat deposition. lncRNA can regulate cell function through a variety of mechanisms, the most studied is the mechanism of action of lncRNA as a miRNA molecular sponge. The purpose of this article is to explore the role of transforming growth factor-beta (TGF-β1) mediated lncRNA in the formation of porcine adipocytes, from the perspective of lncRNA to reveal the effect of TGF-β1 on the differentiation of porcine adipocytes, and provide a new way to improve the quality of pork. Adipocyte differentiation and lipid metabolism have important regulatory effects on the quality of meat from livestock. A variety of transcription factors regulate preadipocyte differentiation. Several studies have revealed that transforming growth factor-beta (TGF-β1) may play a key role in epithelial–mesenchymal transition (EMT); however, little is known about the effects of TGF-β1 treatment on porcine preadipocytes. To explore the role of TGF-β1 in porcine adipocyte differentiation, porcine preadipocytes were treated with 10 ng/mL TGF-β1, and two libraries were constructed for RNA-seq. We chose an abundant and differentially expressed long noncoding RNA (lncRNA), which we named fat deposition-associated long noncoding RNA1 (FDNCR1), for further study. RT-qPCR was used to detect mRNA levels of genes related to adipocyte differentiation. Triglyceride assay kits were used to detect lipid droplet deposition. TGF-β1 significantly suppressed porcine preadipocyte differentiation. We identified 8158 lncRNAs in total and 39 differentially expressed lncRNAs. After transfection with FDNCR1 siRNA, the mRNA expression of aP2, C/EBPα, and PPARγ and triglyceride levels significantly increased. Transfection with FDNCR1 siRNA significantly decreased protein levels of p-Smad2/Smad2 and p-Smad3/Smad3. These results demonstrate that FDNCR1 suppresses porcine preadipocyte differentiation via the TGF-β signaling pathway. [ABSTRACT FROM AUTHOR]

Simple Summary: Yak, which is the predominant and semi-domesticated livestock on the Qinghai-Tibet Plateau, suffers severe starvation and body weight reduction in the cold season because of the harsh highland environment. Lipids are important energy sources to starvation animals. β-hydroxybutyrate (BHBA) that is derived from lipid decomposition as the primary ketone body is with the function not only to provide energy for animals as energy materials, but also regulate lipid metabolism as signaling molecular. However, the effects of starvation and BHBA on lipid metabolism and its mechanism are still unclear for ruminant animals. Herein, we investigated the effects of starvation and intravenous infusion of BHBA solution on Yak growth, serum biochemistry, hormones, subcutaneous adipocyte morphology, fatty acid composition, activity of enzymes related to lipid metabolism, and signal pathway. The results showed that starvation promoted lipid catabolism and BHBA infusion up-regulated the mRNA expression of receptor GPR109A in subcutaneous adipose tissue, inhibited the Cyclic adenosine monophosphate(cAMP)/Protein kinase A (PKA)/cAMP-responsive element binding protein (CREB) signaling pathway, and inhibited lipolysis. Our study was beneficial for enriching the nutrition regulation theory of yaks and improving their growth potential. Lipid is the chief energy source for starved animals. β-hydroxybutyrate (BHBA) is the main ketone body produced by lipid decomposition. In Chinese hamster ovary (CHO) cell experiment, it was found that BHBA could be used not only as an energy substance, but also as a ligand of GPR109A for regulating lipid metabolism. However, whether BHBA can regulate lipid metabolism of yaks, and its effective concentration and signal pathway are not clear. This study investigated the effects and mechanism of starvation and BHBA on the lipid metabolism of yak. Eighteen male Jiulong yaks were selected and then randomly divided into three groups: normal feeding group (NG), starvation group (SG), and starvation with BHBA infusion group (SBG). The yaks in the NG group were freely fed during the trial, while the yaks in the SG and SBG groups fasted; from 7th to 9th days of the experiment, the NG and SG were infused continuous with 0.9% normal saline and SBG was infused 1.7 mmol/L BHBA solution respectively. The blood samples were collected on the 0th, 1st, 3rd, 5th, 7th, and 9th day of experiment. The subcutaneous adipose tissue of all the yaks in this study were taken from live bodies after infusion. Serum glucose, lipid metabolites, hormone concentrations, and mRNA and protein expressions of key factors of lipid metabolism and signaling pathway in subcutaneous adipose tissue were measured. The results showed that, as compared with NG, starvation significantly reduced the body weight of yak in SG, and significantly increased the concentration of BHBA in serum and the mRNA expression of PKA and CREB1 in subcutaneous adipose tissue, while the mRNA expression of MEK, PKC, ERK1/2, the area of adipocytes, and the proportion of saturated fatty acid were decreased. Whereas, further increase of BHBA concentration through infusion promoted the mRNA expression of GPR109A receptor in the subcutaneous adipose tissue of SBG, inhibited the mRNA expression of AC and PKA, and decreased the phosphorylation protein abundance of CREB1, and significantly increased the diameter and area of adipocytes. These findings suggest that starvation led to enhanced lipid catabolism in yaks. An increasing BHBA concentration could increase the mRNA expression of GPR109A receptor in subcutaneous adipose tissue and inhibit the cAMP/PKA/CREB signaling pathway and lipid decomposition. [ABSTRACT FROM AUTHOR]

Simple Summary: Nutrition is one of the main causes of thyroid response and energetic metabolism. Presently, there is a lack of information on the physiological effect of moderate activities in canines, particularly in guide dogs. Aim was to compare the effect of diet on thyroid and lipid status in guide dogs, during a 12-weeks training, fed two commercial diets, one, HPF, characterized by low-carbohydrate/high-protein/high-fat (29:39:19% as fed) and the other, LPF, characterized by high-carbohydrate/low-protein/low-fat (50:24:12% as fed) content. Our hypothesis was that the intake of a diet rich in fat and protein would have given a better response than the carbohydrate-rich diet for thyroid and lipid homeostasis to cope with the increased energy demands of dogs subjected to the training period. Results evidenced that the consumption of a diet rich in fat and protein appears the nutritional plan most suitable to support moderate exercise for guide dogs during the training work; this diet supports maintenance of body weight, Body Condition Score (BCS), and serum baseline thyroid and lipid profiles, offering potential improvements in dogs' performances. However, the chronic ingestion of diets that are extreme in their composition of either fat or carbohydrate should be always approached with caution. Nutrition plays a leading role that most influences thyroid response and energetic metabolism. Aim was to compare the effect of diet on thyroid and lipid status in guide dogs during a 12-weeks training period. Eight Labrador Retrievers were divided into two groups homogeneous for sex, age, body weight, and Body Condition Score (BCS) and fed two commercial diets one, HPF, characterized by low-carbohydrate/high-protein/high-fat (29%:39%:19% as-fed) and the other, LPF, by high-carbohydrate/low-protein/low-fat (50%:24%:12% as-fed) content. The serum thriiodothyronine (T3), thyroxine (T4), cholesterol (CHOL), triglycerides (TAGs) and non-esterified fatty acids (NEFA) were determined at Day 0, 28, 56, and 84, before the daily training. Statistical model included the effects of Diet (HPF vs. LPF) and Time (Day 0 to Day 84), and their interaction. In the HPF group, Diet significantly (p < 0.01) increased T4, CHOL, and TAGs and decreased NEFA. In both groups, Time significantly (p < 0.05) increased T4 and TAGs, CHOL at Day 28, and NEFA at Day 56. The interaction did not influence serum hormones and lipid pattern. The adjustments in thyroid and lipid responses to moderate exercise in HPF group were driven mainly by the nutrient composition of the diet in relation to the involvement of metabolic homeostasis. [ABSTRACT FROM AUTHOR]

Simple Summary: Dairy ewes, just like cows, suffer from the low-fat milk syndrome, also known as milk fat depression (MFD), when marine lipids are added to their diet to modulate milk fatty acid (FA) profile. Alterations in the ruminal metabolism of dietary unsaturated FA seem to be at the core of this MFD but its causative agent has not yet been confirmed. Although some alterations may derive from shifts in oleic acid metabolism, methodological constraints represent a major challenge: the fact that oleic and other dietary FA (e.g., linoleic and linolenic acids) have common intermediates hampers the identification of those metabolites deriving specifically from each one. Thus, we conducted an in vitro trial combining an isotopic tracer approach with the use of rumen inoculum from ewes fed a diet supplemented or not with fish oil (which is known to cause MFD in dairy animals), to provide new insights into shifts in oleic acid metabolism. Fish oil altered the relative contribution of specific pathways, with relevant increments in oxygenated FA, including a major candidate milk fat inhibitor (10-oxo-18:0). Changes in the concentration of trans 18:1 intermediates were also observed. Results are discussed in the context of their potential association with milk fat depression. Shifts in ruminal oleic acid (OA) metabolism have received little research attention but recent studies have suggested their association with marine lipid-induced milk fat depression (MFD) in ewes and cows. Measurement of specific products of OA within the complex mixture of digesta lipids is however challenging. Therefore, this in vitro trial combined the isotopic labelling technique with the use of rumen inoculum from cannulated sheep fed a diet supplemented or not with 2% of fish oil (which has been demonstrated to cause MFD in dairy ruminants) to characterize the metabolism of OA in response to ruminal alterations associated with MFD. The products of 13C-OA after 24 h of incubation were analysed by gas chromatography-combustion isotope ratio mass spectrometry (GC-C-IRMS). Numerous 13C-labeled 18:1 intermediates and oxygenated FA were detected and no elongation or desaturation of 13OA occurred. Diet supplementation with fish oil (i.e., MFD conditions) resulted in no unique metabolites of 13OA but in relevant changes in the relative contribution of specific metabolic pathways. The inhibition of 18:0 saturation caused by this treatment appeared largely attributable to increased oxygenated FA proportion, in particular the candidate milk fat inhibitor 10-oxo-18:0, and warrants further research on the association between MFD and oxygenated FA. Changes in the concentration of 13C-labeled trans 18:1 intermediates but not in cis 18:1, were also observed. [ABSTRACT FROM AUTHOR]