Wutai Guan

Metabolic Transition of Milk Lactose Synthesis and Up-regulation by AKT1 in Sows from Late Pregnancy to Lactation

Lactose plays a crucial role in controlling milk volume by inducing water toward into the mammary secretory vesicles from the mammary epithelial cell cytoplasm, thereby maintaining osmolality. In current study, we determined the expression of several lactose synthesis related genes, including glucose transporters (glucose transporter 1, glucose transporter 8, sodium-glucose cotransporter 1, sodium-glucose cotransporter 3, and sodium-glucose cotransporter 5), lactose synthases (α-lactalbumin and β1,4-galactosyltransferase), and hexokinases (hexokinase-1 and hexokinase-2) in sow mammary gland tissue at day 17 before delivery, on the 1st day of lactation and at peak lactation. The data showed that glucose transporter 1 was the dominant glucose transporter within sow mammary gland and that expression of each glucose transporter 1, sodium-glucose cotransporter 1, hexokinase-1, hexokinase-2, α-lactalbumin, and β1,4-galactosyltransferase were increased (p < 0.05) when the sows transited from late pregnancy to peak lactation. AKT1 over-expressed mammary epithelial cells were then constructed, and the results indicated that AKT1 increases (p < 0.01) the expression of hexokinase-1 and glucose transporter 1. In summary, lactose synthesis was significantly elevated with the increase of milk production and AKT1 could positively regulate lactose synthesis.

Regulation of amino acid transporters in the mammary gland from late pregnancy to peak lactation in the sow

BackgroundMilk protein is crucial for milk quality in sows and health of newborn piglets. Plasma amino acids (AA) in sows are important precursors for milk protein synthesis in the mammary gland. In order to study the regulation of AA transported in sow mammary glands and possible underlying mechanisms, we measured the expression of genes coding for milk proteins, AA transporter expressions, and plasma AA concentrations in sows at three different physiological stages (D-17, D1 and D17 of lactation), and then further investigated the regulation of AA transport across the cell membrane by adaptive mechanisms using pig mammary epithelial cells (PMEC) as an in vitro model. PMEC were cultured in DMEM:F12 with 4 amino acid concentrations (0 × AA complex, 1 × AA complex, 5 × AA complex, and 25 × AA complex). Classes of AA complexes evaluated in this study included neutral AAs (L-Ala + L-Ser + L-Cys), acidic AAs (L-Asp, L-Glu) and neutral + basic AAs (L-Ala + L-Ser + L-Cys + L-Lys).ResultsOur results indicated that mRNA expression of genes coding for milk protein (αs1-casein, αs2-casein, β-casein and κ-casein) increased significantly with the advance of physiological stage (P < 0.05), and plasma concentrations of most AAs including threonine, serine, glutamate, alanine, valine, cysteine, methionine, isoleucine and tyrosine were greater at D1 of lactation compared with D-17 and D17 of lactation (P < 0.05). Additionally, protein and gene expressions of AA transporters including excitatory AA transporter 3 (EAAT3), alanine/serine/cysteine/threonine transporter (ASCT1) and sodium-coupled neutral AA transporter 1 (SNAT2) were greater in lactating sow mammary glands compared with sow mammary glands in late pregnancy (P < 0.05). The mRNA expressions of SLC38A2, SLC1A1, SLC6A14 increased significantly in the cell mediums supplemented with 5 × and 25 × of AA complexes compared with those cells cultured in DMEM/F12 cell medium (P < 0.05). The mRNA expressions of SLC38A, SLC1A4, and SLC6A14 also increased in EBSS cell medium compared to DMEM/F12. However, only mRNA expression of SLC38A decreased when AA complex was added into EBSS (P < 0.05).ConclusionAA transportation was positively regulated in sow mammary glands with the advance of physiological stage from late pregnancy to peak of lactation and AA transporters in PMECs were adaptively regulated by changed AA concentrations.

Leucine Promotes the Growth of Fetal Pigs by Increasing Protein Synthesis through the mTOR Signaling Pathway in Longissimus Dorsi Muscle at Late Gestation

Leucine (Leu) plays an important role in protein synthesis and metabolism. The present study tested whether Leu supplementation in the diet for sows during late pregnancy could improve piglet birth weight, and it also investigated the possible underlying mechanism. Two hundred sows at day 70 of pregnancy were selected and assigned to four groups fed with following four diets until farrowing, respectively: corn and soybean meal-based diet group (CON), CON + 0.40% Leu, CON + 0.80% Leu, and CON + 1.20% Leu. We found that supplementing with 0.80% Leu significantly increased mean piglet birth weight ( P < 0.05). Supplementation with 0.40, 0.80, and 1.20% Leu increased the plasma concentration of Leu, while decreasing the plasma concentrations of valine (Val) and isoleucine (Ile) in both farrowing sows and newborn piglets ( P < 0.05). The protein expressions of amino acid transporters (including LAT1, SNAT1, SNAT2, 4F2hc, and rBAT) in duodenum, jejunum, ileum, longissimus dorsi muscle of newborn piglets, and placenta of sows showed a difference among the CON group and Leu supplemented groups. Expressions of p-mTOR, p-4E-BP1, and p-S6K1 in longissimus dorsi muscle were also enhanced in each of the supplemental Leu groups compared to CON ( P < 0.05). Collectively, these results indicated that 0.40-0.80% Leu supplementation during late gestation enhanced birth weight of fetal pigs by increasing protein synthesis through modulation of the plasma amino acids profile, amino acid transporters expression, and mTOR signaling pathway.

Recent progress of porcine milk components and mammary gland function

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.

Fat encapsulation enhances dietary nutrients utilization and growth performance of nursery pigs1

Encapsulation of fat may facilitate digestion and absorption of fat in nursery pigs. Two experiments were conducted to evaluate 1) effects of encapsulation of palm oil (PO) and coconut oil (CO) on growth performance, feed intake, feed efficiency, and blood parameters, and 2) effects of encapsulation of PO and CO on apparent total tract digestibility (ATTD) of nutrients, and the activity of digestive enzymes in nursery pigs. In Exp. 1, 540 pigs (28 d of age, 8.23 ± 0.22 kg BW) were allotted to five treatments based on a randomized complete block design (as-fed basis). Pigs were fed basal diets with five different fat sources: 6.0% soybean oil (SBO), 6.0% PO, 6.0% PO from encapsulated fat (EPO), 6.0% CO, and 6.0% CO from encapsulated fat (ECO), respectively, with six pens per treatment and 18 pigs per pen for a 4-wk feeding trial. Dried casein and whey powder used for encapsulation were included at identical levels in all diets. Pigs fed EPO had increased (P < 0.05) ADG during days 0 to 14 and overall compared to pigs fed SBO and PO, whereas ADG of pigs fed ECO was not different from pigs fed EPO and CO. There were no differences in ADFI among treatments. Pigs fed EPO had increased G:F (P < 0.05) during days 0 to 14 compared to SBO, PO, and CO. Serum urea nitrogen concentrations in pigs fed EPO, CO, and ECO were lower (P < 0.05) than that of pigs fed SBO and PO. In Exp. 2, 30 pigs (28 d of age, 8.13 ± 0.10 kg BW) were housed individually (n = 6 per treatment) and allotted to five treatments as described in Exp.1. Pigs were fed ad libitum for 4 wk to measure ATTD of diets weekly and digestive enzyme activity at week 4. Pigs fed EPO, CO, and ECO had increased (P < 0.05) ATTD of DM and GE compared to pigs fed SBO and PO. Pigs fed SBO had reduced (P < 0.05) ATTD of CP compared to other treatments. Pigs fed PO had reduced (P < 0.05) ATTD of ether extracts (EE) compared to other treatments. Pigs fed PO had greater (P < 0.05) trypsin activity in the pancreas than pigs fed SBO and CO. Pigs fed PO tended to have lower (P = 0.073) pancreatic lipase activity compared to other treatments, whereas dietary treatments had no effect on pancreatic amylase activity. In conclusion, this study indicates that encapsulation of PO improved growth performance and ATTD of diets in nursery pigs, whereas the limited effects of encapsulated CO were likely due to the high digestibility of the medium-chain triglycerides abundant in CO.