Dairy goats are often fed a high-concentrate (HC) diet to meet their lactation demands; however, long-term concentrate feeding is unhealthy and leads to milk yield and lactose content decreases. Therefore, we tested whether a buffering agent is able to increase the output of glucose in the liver and influence lactose synthesis. Eight lactating goats were randomly assigned to two groups: one group received a HC diet (Concentrate : Forage = 6:4, HG) and the other group received the same diet with a buffering agent added (0.2 % NaHCO3, 0.1 % MgO, BG) over a 19-week experimental period. The total volatile fatty acids and lipopolysaccharide (LPS) declined in the rumen, which led the rumen pH to become stabile in the BG goats. The milk yield and lactose content increased. The alanine aminotransferase, aspartate transaminase, alkaline phosphatase, pro-inflammatory cytokines, LPS and lactate contents in the plasma significantly decreased, whereas the prolactin and growth hormone levels increased. The hepatic vein glucose content increased. In addition, pyruvate carboxylase (PC), phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6PC) expression in the liver was significantly up-regulated. In the mammary glands, the levels of glucose transporter type 1, 8, 12 as well as of sodium-glucose cotransporter 1 increased. Cumulative buffering agent treatment increased the blood concentrations of glucose via gluconeogenesis and promoted its synthesis in the liver. This treatment may contribute to the increase of the milk yield and lactose synthesis of lactating goats.

ABSTRACT. In order to evaluate the effect of high-concentrate diet supplementation on milk protein content, six Holstein dairy cows were assigned into high-concentrate diet (HC) or low-concentrate diet (LC) groups (N = 3/group) for 50 days. With regard to milk protein, HC feeding significantly reduced the percentage of milk protein (P < 0.01), and milk protein yield also reduced. The milk somatic cell count numbers and N-acetyl-D-glucosaminidase activity was significantly higher (P < 0.01) in the HC group than in the LC group. A pre-column derivatization procedure of o-phthalaldehyde was used to analyze the milk amino acid profile, the contents of Asp, Gln, Ala, Ile, Leu, and Lys were significantly lower in milk (P < 0.05), but Arg and Phe were significantly higher (P < 0.05) in the HC group than in the LC group. The mRNA abundance for amino acid transporters SLC7A8, SLC7A10 (P < 0.05), SLC1A3 (P < 0.05), and SLC16A10 (P < 0.05) were decreased in the HC group. These data indicate that expression of amino acid transporters alters regulation of amino acid utilization and decreases milk quality in dairy cows.

Ruminants are often fed a high-concentrate (HC) diet to meet lactating demands, yet long-term concentrate feeding induces subacute ruminal acidosis (SARA) and leads to a decrease in milk fat. Buffering agent could enhance the acid base buffer capacity and has been used to prevent ruminant rumen SARA and improve the content of milk fat. Therefore, we tested whether a buffering agent increases lipid anabolism in the livers of goats and influences of milk fat synthesis. Twelve Saanen-lactating goats were randomly assigned to two groups: one group received a HC diet (Concentrate: Forage=60:40, Control) and the other group received the same diet with a buffering agent added (10 g sodium butyrate, C4H7NaO2; 10 g sodium bicarbonate, NaHCO3; BG) over a 20-week experimental period. Overall, milk fat increase (4.25±0.08 vs. 3.24±0.10; P<0.05), and lipopolysaccharide levels in the jugular (1.82±0.14 vs. 3.76±0.33) and rumen fluid (23,340±134 vs. 42,550±136) decreased in the buffering agent group (P<0.05). Liver consumption and release of nonesterified fatty acid (NEFA) into the bloodstream increased (P<0.05). Phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT) and ribosomal protein S6 kinase (p70S6K) up-regulated significantly in the livers of the buffering agent group (P<0.05). It also up-regulated expression of the transcription factor sterol regulatory element binding protein-1c (SREBP-1c) and its downstream targets involved in fatty acid synthetic, including fatty acid synthetase (FAS), stearoyl-CoA desaturase (SCD-1) and acetyl-CoA carboxylase 1 (ACC1) (P<0.05). The BG diet increased insulin levels in blood (19.43±0.18 vs. 13.81±0.10, P<0.05), and insulin receptor was likewise elevated in the liver (P<0.05). Cumulatively, the BG diet increased plasma concentrations of NEFA by INS-PI3K/AKT-SREBP-1c signaling pathway promoting their synthesis in the liver. The increased NEFA concentration in the blood during BG feeding may explain the up-regulated in the milk fat of lactating goats.