Relationship between rate of glucose or propionate infusion and milk protein yield and concentration in dairy cows: A meta-regression.

Although postruminal glucose infusion into dairy cows has increased milk protein yield in some past experiments, the same trend has not been observed in others. A meta-regression of 64 sets of observations from 29 previously published glucose and propionate infusion studies in dairy cattle, treating study and experiment (study) as random effects, was performed to establish the general effects of glucose equivalent (GlcE) infusion rate on milk true protein (MTP) yield and content, if any, and to identify independent, fixed-effect variables that accounted for the changes in MTP yield and content that were observed. Candidate explanatory variables included rate and site of infusion, diet composition and intake, body weight and lactation stage of the cows, and the change in nutrient intake between GlcE and control treatments. Across all studies, according to a model containing only the random effects of study and experiment, GlcE infusion at an average of 954 g/d increased MTP yield by 26 g/d, on average, whereas mean MTP content was not affected. Backward stepwise elimination of potential explanatory variables from a full mixed model produced a final, reduced model for MTP yield that retained a positive, second-order quadratic effect of infusion rate of GlcE and a positive, linear effect of the change in crude protein intake (CPI) between GlcE treatment and control. This change in CPI due to GlcE infusion ranged from -0.546 to 0.173 kg/d in the dataset. The model fit indicated that when CPI was allowed to drop during GlcE infusion, the effect of GlcE on MTP yield was smaller than when CPI was maintained or increased, in a manifestation of the classic protein:energy interaction. The final reduced model for MTP content contained the same explanatory variables as for MTP yield, plus a negative effect of intravenous compared with gastrointestinal infusion. Overall, the meta-analysis revealed that both MTP yield, and content were positively related to GlcE infusion rate and to the change in CPI between glucose treatment and control.

Review: Influence of postabsorptive metabolism on essential amino acid partitioning in lactating dairy cows.

In the lactating cow, essential amino acids (EAAs) absorbed from the gut are partitioned to mammary and extra-mammary tissues via blood plasma circulation. There is also entry of EAA into plasma from the breakdown of proteins in the cow's body. A balance model across plasma was solved to integrate entry rates of branched-chain (BCAA) and non-branched-chain EAA (NBAA) with their corresponding rate constants for clearance by mammary glands and the remainder of the body, for selected glucose and fat infusion experiments. Endogenous EAA entry from whole-body proteolysis was reduced by glucose and unchanged or increased by fat, the efficiency of net plasma BCAA clearance by mammary and extra-mammary tissues was elevated by glucose but slightly reduced by fat, and the efficiency of extra-mammary NBAA clearance may have decreased during glucose infusion but it was not affected or slightly increased by fat. These differences between glucose and fat responses can be accounted for by insulin and glucagon. Insulin suppresses endogenous EAA entry through mechanistic target of rapamycin complex 1, integrated stress response, and glycogen synthase kinase 3 signaling networks in skeletal muscle. While these networks can also regulate protein synthesis rates in muscle and the extra-mammary body, they exhibit low sensitivities to insulin in lactating ruminants. However, in the mammary glands, via these same networks, insulin stimulates clearance of EAA from plasma, although the drive to maintain a set point for milk protein yield takes precedence over nutritional signals. The glucose-induced increase in mammary BCAA clearance without an effect on NBAA clearance is due to a pronounced decrease in plasma BCAA concentrations. Because NBAAs do not experience a similar decline in concentration, the BCAA effect must be due to their metabolic transformation as opposed to sequestration in proteins. In adipose, the products of BCAA catabolism are lipogenic precursors. We propose that faster lipogenesis in adipose tissue, stimulated by glucose infusion, also promotes the uptake of precursor BCAA from plasma, causing a drop in their circulating concentrations. In addition, insulin stimulates BCAA oxidation in muscle as an alternative fuel to fatty acids. A lower efficiency of extra-mammary NBAA clearance during glucose infusion may be the consequence of decreased hepatic expression of AA-catabolizing enzymes in response to low glucagon concentration. The proportion of EAA entry partitioned to the mammary glands is a culmination of regulatory shifts at all of the points discussed above according to a regulated or unfair competition between mammary and extra-mammary processes.

Exogenous ß-mannanase supplementation improved immunological and metabolic responses in lactating dairy cows.

Exogenous enzymes have been used to improve nutrient utilization in several species of livestock, particularly swine and poultry. In addition, improved immunological and metabolic traits have been reported in nonruminants. The objective of this study was to determine the effects of ß-mannanase supplementation on milk yield and composition, and immunological and metabolic responses in lactating Holstein dairy cows. Two weeks after calving, 20 Holstein cows (10 multiparous and 10 primiparous) were blocked by parity and assigned to 1 of 2 diets for 182 d. All cows were housed in the same environment and fed the same basal diet. The basal diet of the treatment group was supplemented with ß-mannanase (CTCBio Inc., Seoul, South Korea) at 0.1% of concentrate dry matter. No differences were detected between the control and enzyme supplement groups in milk yield parameters or milk composition. Supplementation of ß-mannanase enzyme reduced blood haptoglobin levels in supplemented multiparous cows compared with controls. Furthermore, nonesterified fatty acid concentration levels tended to be lower in cows fed ß-mannanase, regardless of parity. Neither immunoglobulin G nor milk somatic cell count was affected by ß-mannanase supplementation, regardless of parity. The number of insemination services tended to be lower in cows fed diets supplemented with ß-mannanase. Results from this study suggest that supplementation of ß-mannanase exogenous enzyme could help to reduce instances of systemic inflammation and decrease fat mobilization in lactating Holstein cows. Multiparous cows are considered susceptible to acute infections and inflammation; thus, the enzyme had a greater effect in multiparous cows.

Development of a simple, rapid and reproducible HPLC assay for the simultaneous determination of hypericins and stabilized hyperforin in commercial St. John's wort preparations.

A reversed-phase HPLC method was developed and validated for the simultaneous determination of hypericins and stabilized hyperforin in St. John's wort extract. The sample solution was prepared by extraction of the finely powdered extract with methanol-water (80:20, v/v) containing 5% HP-beta-cyclodextrin, and adjusted to pH 2.5 with orthophosphoric acid. Diluted extract solutions, maintained at 0 degrees C, were injected into a C18 column. The samples were eluted isocratically using a mobile phase consisting of acetonitrile and 0.3% v/v phosphoric acid (90:10, v/v) at a 1.5 ml/min flow rate with simultaneous fluorescence (315/590 nm, excitation/emission) and UV (273 nm) detection. Quantification of the marker compounds (hypericin, pseudohypericin, hyperforin) was achieved by use of standard curves generated by plotting peak heights versus concentrations. Validation studies demonstrated that this HPLC method is simple, rapid, reliable, and reproducible. The standard curves were linear over the concentration ranges, 0.5-2.5 microg/ml (hypericin), 0.35-1.6 microg/ml (pseudohypericin) and 5-50 microg/ml (hyperforin). The intra-day coefficients of variation obtained for hypericin, pseudohypericin and hyperforin were < or = 4.4%, < or = 5.4%, and < or = 2.8%, respectively; inter-day CVs were < or = 5.8%, < or = 4.9%, and < or = 2.5%, respectively. This method may be applied for the routine standardization of St. John's wort products against hyperforin and the hypericins, the putative antidepressant principles in the herbal.

Glucosamine and chondroitin sulfates in the treatment of osteoarthritis: a survey.

For more than 30 years, non-steroidal anti-inflammatory drugs (NSAIDs) have been used as standards in the treatment of osteoarthritis (OA). Serious and often life-threatening adverse effects due to these agents are common. Clinical findings have revealed that glucosamine sulfate and chondroitin sulfate are effective and safer alternatives to alleviate symptoms of OA. Experimental evidence indicates that these compounds and their low molecular weight derivatives have a particular tropism for cartilage where they serve as substrates in the biosynthesis of component building blocks. This paper is a literature review of the chemistry, mechanism of action, pharmacokinetics, clinical efficacy and safety of these two nutraceuticals.