The current study aims to confirm the positive effects of dietary nano-Se on nutrients deposition and muscle fibre formation in grass carp fed with high-fat diet (HFD) before overwintering and to reveal its possible molecular mechanism. The lipid deposition, protein synthesis and muscle fibre formation in grass carp fed with regular diet (RD), HFD or HFD supplemented with nano-Se (0·3 or 0·6 mg/kg) for 60 d were tested. Results show that nano-Se significantly reduced lipid content, dripping loss and fibre diameter (P < 0·05), but increased protein content, post-mortem pH24 h and muscle fibre density (P < 0·05) in muscle of grass carp fed with HFD. Notably, dietary nano-Se decreased lipid deposition in the muscle by regulating amp-activated protein kinase activity and increased protein synthesis and fibre formation in muscle by activating target of rapamycin and myogenic determining factors pathways. In summary, dietary nano-Se can regulate the nutrients deposition and muscle fibre formation in grass carp fed with HFD, which exhibit potential benefit for improving flesh quality of grass carp fed with HFD.

The increasing use of unconventional feedstuffs in chicken’s diets results in the substitution of starch by lipids as the main dietary energy source. To evaluate the responses of genetically fat or lean chickens to these diets, males of two experimental lines divergently selected for abdominal fat content were fed isocaloric, isonitrogenous diets with either high lipid (80 g/kg), high fiber (64 g/kg) contents (HL), or low lipid (20 g/kg), low fiber (21 g/kg) contents (LL) from 22 to 63 days of age. The diet had no effect on growth performance and did not affect body composition evaluated at 63 days of age. Glycolytic and oxidative energy metabolisms in the liver and glycogen storage in liver and Sartorius muscle at 63 days of age were greater in chicken fed LL diet compared with chicken fed HL diet. In Pectoralis major (PM) muscle, energy metabolisms and glycogen content were not different between diets. There were no dietary-associated differences in lipid contents of the liver, muscles and abdominal fat. However, the percentages of saturated (SFA) and monounsaturated fatty acids (MUFA) in tissue lipids were generally higher, whereas percentages of polyunsaturated fatty acids (PUFA) were lower for diet LL than for diet HL. The fat line had a greater feed intake and average daily gain, but gain to feed ratio was lower in that line compared with the lean line. Fat chickens were heavier than lean chickens at 63 days of age. Their carcass fatness was higher and their muscle yield was lower than those of lean chickens. The oxidative enzyme activities in the liver were lower in the fat line than in the lean line, but line did not affect energy metabolism in muscles. The hepatic glycogen content was not different between lines, whereas glycogen content and glycolytic potential were higher in the PM muscle of fat chickens compared with lean chickens. Lipid contents in the liver, muscles and abdominal fat did not differ between lines, but fat chickens stored less MUFA and more PUFA in abdominal fat and muscles than lean chickens. Except for the fatty acid composition of liver and abdominal fat, no interaction between line and diet was observed. In conclusion, the amount of lipids stored in muscles and fatty tissues by lean or fat chickens did not depend on the dietary energy source.

Carnitine has been reported to improve growth performance and reduce body lipid content in fish. Thus, we hypothesised that carnitine supplementation can improve growth performance and reduce lipid content in the liver and muscle of yellow catfish (Pelteobagrus fulvidraco), a commonly cultured freshwater fish in inland China, and tested this hypothesis in the present study. Diets containing l-carnitine at three different concentrations of 47 mg/kg (control, without extra carnitine addition), 331 mg/kg (low carnitine) and 3495 mg/kg (high carnitine) diet were fed to yellow catfish for 8 weeks. The low-carnitine diet significantly improved weight gain (WG) and reduced the feed conversion ratio (FCR). In contrast, the high-carnitine diet did not affect WG and FCR. Compared with the control diet, the low-carnitine and high-carnitine diets increased lipid and carnitine contents in the liver and muscle. The increased lipid content in the liver could be attributed to the up-regulation of the mRNA levels of SREBP, PPARγ, fatty acid synthase (FAS) and ACCa and the increased activities of lipogenic enzymes (such as FAS, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and malic enzyme) and to the down-regulation of the mRNA levels of the lipolytic gene CPT1A. The increased lipid content in muscle could be attributed to the down-regulation of the mRNA levels of the lipolytic genes CPT1A and ATGL and the increased activity of lipoprotein lipase. In conclusion, in contrast to our hypothesis, dietary carnitine supplementation increased body lipid content in yellow catfish.

Predicting aspects of pork quality becomes increasingly important from both a nutritional and technological point of view. The aim of the present study was to provide quantitative information on the relation between nutrient intake and whole-body fatty acid (FA) deposition. This information is essential to develop mechanistic models predicting the FA content of tissues. A serial slaughter study was carried out in which thirty pigs were slaughtered between 90 and 150 kg. The diet included 15 g/kg soyabean oil and contained 44 g/kg fat. Only 0·31 and 0·40 of the digested n-6 and n-3 FA were deposited, respectively. Approximately one-third of the n-3 supply that was deposited resulted from the conversion of 18 : 3 to other metabolites (i.e. EPA, docosapentaenoic acid and DHA). This proportion was affected by the pig genotype. De novo-synthesised FA represented 0·86 of the total non-essential FA deposition, and its average composition corresponded to 0·017, 0·286, 0·025, 0·217 and 0·454 for 14 : 0, 16 : 0, 16 : 1, 18 : 0 and 18 : 1, respectively. Although the average whole-body FA composition was relatively constant during the finishing period, this was not so for the tissues. In the carcass (without backfat), the content of 18 : 1 increased during the finishing period, whereas that of 16 : 0 and 18 : 0 decreased. Backfat captured a proportionally greater fraction of 18 : 2 than did the carcass or the residual tissues. In contrast, a proportionally greater fraction of the dietary 18 : 3 supply was deposited in the carcass compared to other tissues.

Predicting aspects of pork quality becomes increasingly important from both a nutritional and a technological point of view. Little information is, however, available concerning the quantitative relation between nutrient intake and fatty acid (FA) deposition at the whole-animal level. In this study, eight blocks of five littermate barrows were used in a comparative slaughter trial. At 24 kg body weight (BW), one pig from each litter was slaughtered to determine the initial FA composition. The other littermates were assigned to one of four feeding levels (ranging from 70 % to 100 % of intake ad libitum) and were given a diet containing 0·36 g/kg lipid and 0·22 g/kg FA. The temperature for each block was maintained at either 23 or 30°C. At 65 kg, the pigs were slaughtered and the body lipid and FA composition was determined. Seventy per cent of the digested n-6 FA and 50 % of the n-3 FA were deposited. The average composition of de novo synthesised FA corresponded to 1·7, 30·3, 2·4, 19·7 and 45·9 % for 14: , 16: , 16: 1, 18: and 18: 1 FA, respectively. At 23°C and for feeding ad libitum, 33 % of 16: FA was deposited, 1·7 % shortened to 14: , 63 % elongated to 18: and 2·8 % unsaturated to 16: 1. Twenty-eight per cent of 18: FA was deposited and 72 % unsaturated to 18: 1. At 30°C, 18: FA desaturation was reduced by 3·5 %. Feed intake and temperature independently affected the elongation of 16: FA. A reduction in feed intake increased the elongation rate, whereas the increase in temperature reduced the elongation rate.