Optimizing dietary rumen-degradable starch to rumen-degradable protein ratio improves lactation performance and nitrogen utilization efficiency in mid-lactating Holstein dairy cows.

The dietary rumen-degradable starch (RDS) to rumen-degradable protein (RDP) ratio, denoted as the RDS-to-RDP ratio (SPR), has been proven to enhance in vitro rumen fermentation. However, the effects of dietary SPR in vivo remain largely unexplored. This study was conducted to investigate the effect of dietary SPR on lactation performance, nutrient digestibility, rumen fermentation patterns, blood indicators, and nitrogen (N) partitioning in mid-lactating Holstein cows. Seventy-two Holstein dairy cows were randomly assigned to three groups (24 head/group), balanced for (mean ± standard deviation) days in milk (116 ± 21.5), parity (2.1 ± 0.8), milk production (42 ± 2.1 kg/d), and body weight (705 ± 52.5 kg). The cows were fed diets with low (2.1, control), medium (2.3), or high (2.5) SPR, formulated to be isoenergetic, isonitrogenous, and iso-starch. The study consisted of a one-week adaptation phase followed by an eight-week experimental period. The results indicated that the high SPR group had a lower dry matter intake compared to the other groups (p < 0.05). A quadratic increase in milk yield and feed efficiency was observed with increasing dietary SPR (p < 0.05), peaking in the medium SPR group. The medium SPR group exhibited a lower milk somatic cell count and a higher blood total antioxidant capacity compared to other groups (p < 0.05). With increasing dietary SPR, there was a quadratic improvement (p < 0.05) in the total tract apparent digestibility of crude protein, ether extract, starch, neutral detergent fiber, and acid detergent fiber. Although no treatment effect was observed in rumen pH, the rumen total volatile fatty acids concentration and microbial crude protein synthesis increased quadratically (p < 0.05) as dietary SPR increased. The molar proportion of propionate linearly increased (p = 0.01), while branched-chain volatile fatty acids linearly decreased (p = 0.01) with increasing dietary SPR. The low SPR group (control) exhibited higher concentration of milk urea N, rumen ammonia N, and blood urea N than other groups (p < 0.05). Despite a linear decrease (p < 0.05) in the proportion of urinary N to N intake, increasing dietary SPR led to a quadratic increase (p = 0.01) in N utilization efficiency and a quadratic decrease (p < 0.05) in the proportion of fecal N to N intake. In conclusion, optimizing dietary SPR has the potential to enhance lactation performance and N utilization efficiency. Based on our findings, a medium dietary SPR (with SPR = 2.3) is recommended for mid-lactating Holstein dairy cows. Nevertheless, further research on rumen microbial composition and metabolites is warranted to elucidate the underlying mechanisms of the observed effects.

Effects of dietary palmitic acid and oleic acid ratio on milk production, nutrient digestibility, blood metabolites and milk fatty acids profile of lactating dairy cows.

Adequate energy supply is a crucial factor for maintaining the production performance in early lactating cows. Adding fatty acids to diets can improve energy supply, while the effect could be related to the chain length and degree of saturation of fatty acids. This study was conducted to evaluate the effect of different ratios of palmitic acid (C16:0) to oleic acid (cis-9 C18:1) on the production performance, nutrient digestibility, blood metabolites and milk fatty acids profile in early lactating dairy cows. Seventy-two multiparous Holstein cows (63.5 ± 2.61 d in milk) blocked by parity (2.39 ± 0.20), body weight (668.3 ± 20.1 kg), body condition score (3.29 ± 0.06), and milk yield (47.9 ± 1.63 kg) were used in a completely randomized design. Cows were divided into 3 groups with 24 cows in every group. Cows in 3 treatments were provided iso-energy and iso-nitrogen diets, whereas the C16:0 to cis-9 C18:1 ratio was different: (1) 90.9% C16:0 + 9.1% cis-9 C18:1 (90.9:9.1); (2) 79.5% C16:0 + 20.5% cis-9 C18:1 (79.5:20.5); (3) 72.7% C16:0 + 27.3% cis-9 C18:1 (72.7:27.3). Fatty acids were added at 1.3% in dry matter basis. Although the dry matter intake fat-corrected milk yield and energy-corrected milk yield were not affected, the milk yield, milk protein yield and feed efficiency increased linearly with the increasing of cis-9 C18:1 ratio. The milk protein percentage and milk fat yield did not differ among treatments, whereas the milk fat percentage tended to decrease linearly with the increasing of cis-9 C18:1 ratio. The lactose yield increased linearly and lactose percentage tended to increase linearly with increasing cis-9 C18:1 ratio, whereas the percentage of milk total solids and somatic cell count decreased linearly. Though the changes of body condition score were not affected by treatments, the body weight loss decreased linearly with the increasing of cis-9 C18:1 ratio. The effect of treatment on nutrient digestibility was limited, except a linear increase in ether extract and neutral detergent fiber digestibility with the increasing of cis-9 C18:1 ratio. There was a linear increase in the concentrations of plasma glucose, whereas the triglyceride and nonesterified fatty acid concentration decreased linearly with the increasing of cis-9 C18:1 ratio. As the cis-9 C18:1 ratio increased, the concentration of de novo fatty acids decreased quadratically, while the mixed and preformed fatty acids increased linearly. In conclusion, increasing cis-9 C18:1 ratio could increase production performance and decrease body weight loss by increasing nutrient digestibility, and the ratio had the most powerful beneficial effect on early lactating cows suggested by 72.7:27.3.

Effect of Dietary Rumen-Degradable Starch to Rumen-Degradable Protein Ratio on In Vitro Rumen Fermentation Characteristics and Microbial Protein Synthesis.

The objective of this study was to investigate the effects of dietary rumen-degradable starch (RDS, g/kg of DM) to rumen-degradable protein (RDP, g/kg of DM) ratios (SPR) on in vitro rumen fermentation characteristics and microbial protein synthesis (MCPS). Treatments were eight diets with SPR of 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 and 2.6 and were formulated to be isoenergetic, isonitrogenous, and isostarch. Substrates were anaerobically incubated in sealed culture vials (100 mL) for 6, 24 or 48 h. Three incubation runs were conducted within two consecutive weeks. With the increase of the dietary SPR, the gas production (GP), in vitro dry matter disappearance (IVDMD) and concentration of MCPS and total volatile fatty acids (TVFA) linearly increased after 6 h of incubation (p ≤ 0.01), whereas they quadratically increased and peaked at the SPR of 2.3 after 24 and 48 h of incubation (p < 0.05). In response to dietary SPR increasing, the in vitro neutral detergent fiber disappearance (IVNDFD) quadratically increased (p < 0.01), and the ammonia nitrogen (NH3-N) concentration linearly decreased (p < 0.01) after 6, 24 and 48 h of incubation. Based on the presented results, an SPR of 2.3 is recommended for formulating a diet due to its greatest IVDMD, IVNDFD, GP, TVFA and MCPS. However, as the results obtained are strictly dependent on the in vitro conditions, further in vivo studies are needed to verify our findings.

Vitamin E regulates bovine granulosa cell apoptosis via NRF2-mediated defence mechanism by activating PI3K/AKT and ERK1/2 signalling pathways.

High-yield dairy cows are usually subject to high-intensive cell metabolism and produce excessive reactive oxygen species (ROS). Once ROS is beyond the threshold of scavenging ability, it can induce oxidative stress, imperilling the reproductive performance of cows. The study was to investigate the effects of vitamin E (VE) on H2 O2 -induced proliferation and apoptosis of bovine granulosa cells and the underlying molecular mechanism. Granulosa cells were pretreated with VE for 24 hr and then treated with H2 O2 for 6 hr. The results showed that VE treatment decreased the intracellular ROS levels, increased the MDA content, and improved the antioxidant enzyme activity in a dose-dependent manner. Furthermore, VE treatment promoted the proliferation and inhibited apoptosis in granulosa cells by up-regulation of CCND1 and BCL2 levels and down-regulation of P21, BAX, and CASP3 levels. The cytoprotective effects of VE were attributed to the activation of the NRF2 signalling pathway. Knockdown of the NRF2 impaired the cytoprotective effects of VE on granulosa cells. Besides, the PI3K/AKT and ERK1/2, but not the p38 signalling pathway is involved in the regulation of VE-mediated cell proliferation and apoptosis. The PI3K/AKT inhibitor LY294002 and ERK1/2 inhibitor SCH772984 inhibited the VE-induced granulosa cell proliferation and promoted apoptosis, whereas the p38 inhibitor SB203580 had the opposite effects. These results were confirmed by proliferation and apoptosis-related gene expression at mRNA and protein levels. The results also showed that the PI3K/AKT inhibitor LY294002 and ERK1/2 inhibitor SCH772984 inhibited VE-induced NRF2, GCLC, GCLM, and HO-1 expression, whereas the p38 inhibitor SB203580 not. Overall, the results demonstrated that VE-regulated granulosa cell proliferation and apoptosis via NRF2-mediated defence system by activating the PI3K/AKT and ERK1/2 signalling pathway.

Vitamin E and selenium supplementation synergistically alleviate the injury induced by hydrogen peroxide in bovine granulosa cells.

Dairy cows are susceptible to reproductive disorders, which are thought to be associated with oxidative stress. In the study, we investigated the effects of vitamin E (VE) and selenium (Se) on the proliferation, apoptosis, and steroidogenesis in bovine ovarian granulosa cells under hydrogen peroxide (H2O2) - induced oxidative stress and elaborated the underlying mechanisms. Our results showed that VE or Se could stimulate the granulosa cell proliferation, possibly due to up-regulating the expression of CCND1 and decreasing the P21 levels under oxidative stress. VE or Se treatment also increased the secretion of estradiol (E2) and progesterone (P4), which could be owing to improving the expression of genes associated with steroidogenesis (StAR, HSD3ß1, and CYP19A1) expression. VE or Se treatment down-regulated the apoptosis-related genes (BAX, CASP3) expression and decreased cell apoptosis. Furthermore, VE or Se treatment inhibited reactive oxidative species (ROS) and malondialdehyde (MDA) generation, increased total antioxidant capacity (T-AOC), and the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px). Additionally, VE or Se treatment also alleviated the endoplasmic reticulum stress, activated the nuclear factor erythroid 2-related factor 2 (NRF2), and up-regulated the expression of its downstream genes, including NQO1, HO-1, GCLM, GCLC. More importantly, compared with either VE or Se treatment alone, their combined treatment showed a better protective effect against oxidative damage. Overall, our results indicated that VE and Se synergistically stimulated the granulosa cell proliferation and steroidogenesis, decreased cell apoptosis, mitigated the endoplasmic reticulum stress by activating the NRF2 signal pathway.