Effects of monensin on volatile fatty acid metabolism in periparturient dairy cows using compartmental analysis

EFFECTS OF DIETARY SODIUM MONENSIN ON THE METABOLIC AND HORMONAL PROFILES OF DAIRY GOATS DURING THE PERIPARTUM PERIOD

Abstract This study aimed to investigate the energetic and hormonal profiles of dairy goats fed diets supplemented with monensin during the peripartum period. Eleven pregnant Saanen goats were subdivided into two random groups, a control group (GC) and the monensin group (MG). The MG group received 40 mg sodium monensin per animal per day for 15 days before partum and throughout the subsequent experimental period. Clinical observations and sample collection were performed at 30, 15, and 7 days before birth; on the day of partum; and at 5, 15, and 30 days after birth. The following biochemical and hormonal profile variables analyzed were: cholesterol, triglycerides, glucose, fructosamine, non-esterified fatty acids (NEFAs) and β-hydroxybutyrate (BHB), cortisol, and insulin. The ruminal fluid pH, chloride content, and volatile fatty acids were also measured. Statistical analysis of the data was performed using repeated measures ANOVA (p < 0.05) and Pearson's correlation. At partum, the MG group had lower values of NEFAs and lower acetate/propionate ratio. MG had higher triglycerides during the entire experiment period. The administration of monensin generated benefits in terms of energy parameters, improving the metabolic status of the dairy goats during peripartum.

Effects of monensin on glucose metabolism in transition dairy cows

Eight multiparous periparturient Holstein cows fitted with ruminal cannula were used in a split plot design to evaluate the effects of monensin on plasma glucose metabolism. Diets were top-dressed daily with 0 mg/cow of monensin (control) or 300 mg/cow of monensin (MON) both pre- and postpartum. Plasma glucose kinetic parameters on d -13 ± 2.0 and 19 ± 1.6 relative to parturition were determined by using stable isotopes. Na-1-¹³C₃-Propionate (labeled propionate) was infused into the rumen to measure glucose synthesis originating from ruminal propionate, and U-¹³C-glucose (labeled glucose) was injected into the jugular vein to determine total glucose kinetics. A sampling period of 480 min following labeled glucose injection was implemented. A compartmental analysis was employed to determine steady state glucose kinetic parameters. To develop a steady state glucose model, the Windows version of SAAM software (WinSAAM) was used. A 4-compartment model was adequate to comprehensively describe plasma glucose metabolism. The main model compartments consisted of propionate and plasma glucose. The time frame of the 480-min sampling period post-tracer glucose infusion allowed accurate quantification of glucose metabolism. The model estimated that glucose input from sources other than ruminal propionate decreased with MON, from 2.26 to 1.09 g/min postpartum. Gluconeogenesis, expressed as the propionate contribution to the plasma glucose pool, increased in cows fed MON (22 vs. 31%), whereas glucose oxidation, expressed as the glucose disposal rate, significantly decreased (1.67 vs. 0.92 g/min). In conclusion, MON may improve the energy status of transition cows by (1) improving the efficiency of propionate to produce glucose and (2) decreasing glucose oxidation in body tissues.

Evaluation of predictions of volatile fatty acid production rates by the Molly cow model

Predicting ruminal volatile fatty acid (VFA) production is important, as VFA are an energy source to the animal, affect nutrient partitioning, and dictate methane production. The VFA production submodel in the Molly cow model was evaluated using data from 8 publications that reported VFA production rates for cattle. Evaluations were conducted with ruminal water balance predictions enabled and the ruminal VFA stoichiometry coefficients set to "mixed" for all diets, or "mixed" when forage represented between 20 and 80% of the diet, "concentrate" when <20% forage, or "forage" when >80% forage. Prediction errors were relatively insensitive to changes in VFA coefficients by diet type. Root mean square prediction errors (RMSPE) were 63, 63, and 49% for acetate, propionate, and butyrate production rates, respectively. A large proportion of the error was slope bias for acetate and butyrate, and a modest proportion for propionate. Because interconversions between acetate and propionate represent approximately 15% of the variation in net production rates, lack of such consideration in the model may contribute to the substantial model prediction errors. The potential of using thermodynamic equations to predict interconversions was assessed using observed ruminal pH and VFA concentrations from 2 studies and assuming constant hydrogen pressure and concentrations of CO₂, H₂O, adenosine diphosphate, ATP, and inorganic P. Rate constants for conversion of acetate to propionate and propionate to acetate were derived independently from the control treatments and used to predict the fluxes for the other treatment. The observed changes in VFA concentrations and pH explained the observed changes in conversion of acetate to propionate, but overpredicted the change in the propionate to acetate flux in one study. When applied to the other study, the equations predicted the increase in propionate to acetate flux, but failed to predict the observed reduction in acetate to propionate flux. The inability to predict responses accurately may be due to a lack of data for controlling factors other than pH and VFA concentrations.