Methionine (Met) and leucine (Leu) are key amino acids that stimulate milk protein synthesis in bovine mammary epithelial cells (BMEC) via the mTOR signaling pathway. This study reveals that MRCKα (myotonic dystrophy-related CDC42-binding kinase alpha) is a critical mediator in this process. At optimal doses (0.6 mM), Met and Leu increased β-casein production and activated mTOR and PI3K signaling. Silencing MRCKα blocked these effects, confirming its role downstream of PI3K and upstream of PKB. These findings uncover a novel regulatory mechanism in milk biosynthesis and offer molecular targets for enhancing milk quality and yield in dairy production.
Tag: dairy cows
Effects of low dietary cation-anion difference induced by ruminal ammonium chloride infusion on performance, serum, and urine metabolites of lactating dairy cows
Effects of Radix Bupleuri extract supplementation on lactationperformance and rumen fermentation in heat-stressedlactating Holstein cows
Radix Bupleuri extract (RBE) has been shown to mitigate negative effects of high ambient temperature. This experiment was conducted to investigate effects of RBE supplementation on lactation performance and rumen fermentation in Holstein cows under heat stress. Forty Holstein cows (75 ± 15 d in milk, 37.5 ± 1.8 kg of milk/d, and 1.7 ± 0.4 parity) were randomly assigned to one of four groups (n = 10). One of four treatment diets, assigned randomly to one of four groups, consisted of RBE supplementation at 0, 0.25, 0.5 or 1.0 g/kg of the basal diet (concentrate and roughage) based on dry matter (DM). Cows were housed in a tie-stall barn and were individually fed the treatment diets. The experiment lasted for 10 wk in hot summer. During the experiment, average ambient temperatures and temperature-humidity indexes (THI) were respectively 27.5 ± 1.5, 29.8 ± 1.9 and 28.1 ± 1.7 °C, and 78.2 ± 2.7, 79.8 ± 3.3 and 78.3 ± 3.4 at 0600, 1400 and 2200 h. Average respiration rates (RR) with RBE at 0.25, 0.50 and 1.0 g/kg were 65.6, 60.3 and 67.4, respectively, vs. 71.4 (breaths/min) for the control (P < 0.01). Average rectal temperatures (RT) were 39.1, 39.0 and 39.1 vs. 39.3 °C for the control (P < 0.01). Moreover, cows supplemented with RBE increased dry matter intake (DMI, 22.8, 21.6 and 22.1 vs. 20.9 kg/d) (P < 0.05) and milk production (34.2, 33.4 and 32.4 vs. 31.6 kg/d) (P < 0.01) compared with control. Percentages of milk protein and fat were similar among groups, while milk protein yield increased with increasing level of RBE (0.97, 0.95 and 0.92 vs. 0.89 kg/d for the control) (P < 0.01). Milk fat yield also increased with RBE (1.13, 1.12 and 1.09 vs. 1.02 kg/d for the control) (P < 0.05). There was no treatment effect on diet apparent digestibility or volatile fatty acid (VFA) concentration among groups. Overall, supplemental RBE at 0.25 or 0.5 g/kg could mitigate the negative effects of heat stress on production in lactating Holstein cows.
Milk production and composition responds to dietary neutral detergent fiber and starch ratio in dairy cows
This study was designed to investigate whether dietary neutral detergent fiber (NDF):starch ratio could be considered as a nutritional indicator to evaluate carbohydrate composition and manipulate milk production and composition synthesis. Eight primiparous dairy cows were assigned to four total mixed rations with NDF:starch ratios of 0.86, 1.18, 1.63 and 2.34 from T1 to T4 in a replicated 4×4 Latin square design. Dry matter intake and milk production were decreased from T1 to T4. Digestibility of dry matter, organic matter, NDF and crude protein were linearly decreased from T1 to T4. As NDF:starch ratio increased, milk protein content and production, and milk lactose content and production were linearly reduced. However, milk fat content was linearly increased from T1 to T4. Quadratic effect was observed on milk fat production with the highest level in T3. Averaged rumen pH was linearly increased from T1 to T4, and subacute rumen acidosis occurred in T1. Ruminal propionate and butyrate concentration were linearly decreased, and microbial crude protein and metabolizable protein decreased from T1 to T4. It is concluded that NDF:starch ratio can be considered as a potential indicator to evaluate dietary carbohydrate composition and manipulate milk production and composition synthesis.