As the only nutritional source for newborn piglets, porcine colostrum and milk contain critical nutritional and immunological components including carbohydrates, lipids, and proteins (immunoglobulins). However, porcine milk composition is more complex than these three components. Recently, scientists identified additional and novel components of sow colostrum and milk, including exosomes, oligosaccharides, and bacteria, which possibly act as biological signals and modulate the intestinal environment and immune status in piglets and later in life. Evaluation of these nutritional and non-nutritional components in porcine milk will help better understand the nutritional and biological function of porcine colostrum and milk. Furthermore, some important functions of the porcine mammary gland have been reported in recent published literature. These preliminary studies hypothesized how glucose, amino acids, and fatty acids are transported from maternal blood to the porcine mammary gland for milk synthesis. Therefore, we summarized recent reports on sow milk composition and porcine mammary gland function in this review, with particular emphasis on macronutrient transfer and synthesis mechanisms, which might offer a possible approach for regulation of milk synthesis in the future.Electronic supplementary materialThe online version of this article (10.1186/s40104-018-0291-8) contains supplementary material, which is available to authorized users.

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Branched chain amino acids (BCAAs) modulate the intestinal CCK secretion through the T1R1/ T1R3 amino acid receptor.

It is known that heat stress induces various physiological challenges in livestock production including changes in lipid metabolism. However, the molecular mechanism of how heat stress regulates lipid metabolism at the mRNA level is still largely unknown. N 6 -methyl-adenosine (m 6 A) is the most common and abundant modification on RNA molecules present in eukaryotes, which affects almost all aspects of RNA metabolism and thus gives us the hint that it may participate in changes of gene expression of lipid metabolism during heat stress. Therefore, the purpose of the present study was to investigate the effect of heat stress on fat metabolism in 21-day Large White × Landrace piglets from sows challenged by heat stress from day 85 of gestation until day 21 of lactation. We measured the expression of heat shock proteins (HSPs), genes associated with lipid metabolism, m 6 A-related enzymes, and m 6 A levels in abdominal fat and liver of offspring piglets. Our results showed that high ambient temperature significantly increased the expression of HSP70 (P < 0.01) in both liver and abdominal fat and upregulated HSP27 in the liver (P < 0.05). Additionally, genes involved in fat metabolism such as ACACA, FASN, DGAT1, PPAR-γ, SREBP-1c, and FABP4 were upregulated in abdominal fat in the experimental group challenged by high ambient temperature. In the liver, heat stress increased the mRNA expression of DGAT1, SREBP-1c, and CD36 and decreased ATGL and CPT1A expression (P < 0.05). The m 6 A level was higher in the heat stress group compared with the control group in the liver and abdominal fat of offspring piglets (P < 0.01). Notably, heat stress also increased gene expression of METTL14, WTAP, FTO, and YTHDF2 (P < 0.05) in both abdominal fat and liver. The protein abundances of METTL3, METTL14, and FTO were upregulated after heat stress in abdominal fat (P < 0.05) but not in the liver. Although there was no difference in the protein abundance of YTHDF2 in abdominal fat, its level was increased in the liver (P < 0.05). In conclusion, our findings showed that heat stress increased expression of genes involved in lipogenesis, which provided scientific evidence to the observation of increased fatness in pigs under heat stress. We also demonstrated a possible mechanism that m 6 A RNA modification may be associated with these changes in lipid metabolism upon heat stress.

Background: Fat percentage and distribution in pigs are associated with their productive efficiency and meat quality. Dietary branched-chain amino acids (BCAA) regulate fat metabolism in weanling piglets with unknown mechanism. It is reported that N6-methyl-adenosine (m 6 A) is involved in fat metabolism in mice. The current study was designed to investigate the relationship between dietary branched-chain amino acids and fat metabolism through N6-methyl-adenosine (m 6 A) in weanling piglets. Methods: A total of 18 healthy crossbred weaned piglets (Duroc × Landrace × Large White, 10.45 ± 0.41 kg) were divided into 3 treatments and were fed the low BCAA dose diet (L-BCAA), the normal dose BCAA diet (N-BCAA), or the high dose BCAA (H-BCAA) diet for 3 weeks. Results: Our results show that compared with the N-BCAA group, the L-BCAA group had higher concentration of serum leptin (P < 0.05), while the H-BCAA group had lower concentration of serum adiponectin (P < 0.05). Fatty acid synthesis in pigs from the H-BCAA group was lower than those from the N-BCAA group with the down-regulation of lipogenic genes (ACACA, FASN, PPAR-r, SREBP-1c in ventral and dorsal fat, SREBP-1c in liver) and up-regulation of lipolysis genes (HSL, ATGL, CPT-1A, FABP4 in ventral fat, HSL in liver) (P < 0.05). Similarly, fatty acid synthesis in pigs from the L-BCAA group was also lower than those from the N-BCAA group with the decrease of lipogenic genes (ACACA in ventral, ACACA and FASN in dorsal fat, ACACA, FASN, SREBP-1c in liver) and the increase of lipolysis genes (ATGL, CPT-1A CD36, FABP4 in ventral fat and HSL, ATGL, CPT-1A in dorsal fat, CPT-1A) (P < 0.05). Feeding H-BCAA diet significantly reduced total m 6 A levels in ventral and dorsal fat and liver tissues (P < 0.05). The decrease of total m 6 A is associated with down-regulation of METTL3, METTL14 and FTO in dorsal fat and METTL3 and FTO in liver (P < 0.05). Decreased m 6 A modification of ACACA and FASN in ventral and dorsal adipose tissues was observed in pig fed with excessive BCAA. Conclusion: These results suggest that insufficient or excessive BCAA decreased the fat deposition by increasing lipolysis and deceasing lipogenesis in adipose and liver tissues. Dietary excessive BCAA might regulate the process of lipid metabolism partly through the m 6 A RNA methylation.