Prepartum skeletal muscle reserves and branched-chain volatile fatty acid supplementation have minimal effects in response to intravenous glucose tolerance tests in periparturient dairy cattle

Periparturient dairy cows experience metabolic adaptations to prepare for increased nutrient requirements of the fetus and the onset of lactation. Adaptations include increased peripheral tissue insulin resistance, which can be evaluated experimentally using intravenous glucose tolerance tests (IVGTT). The objective of this study was to determine if prepartum skeletal muscle reserves and supplementation of branched-chain volatile fatty acids (BCVFA) in the prepartum period affected blood glucose, β-hydroxybutyrate (BHB), and insulin concentrations 2 wk prepartum and 1 wk postpartum utilizing an IVGTT. At 42 d before expected calving (BEC), the longissimus dorsi muscle depth was measured from an ultrasound image, and based on muscle depth, cows were assigned to either the high muscle (HM; >4.6 cm, n = 17) or low muscle (LM; ≤4.6 cm, n = 17) group. Cows were randomly assigned to either the branched-chain volatile fatty acid (BCVFA) treatment (fed as 39.1 g/d isobutyrate product; 19.4 g/d isovalerate product; 19.6 g/d 2-methylbutyrate product, all on a DM basis) or control (73.0 g/d soyhull pellets on a DM basis) treatment, which were top-dressed daily. Assignment to muscle group and treatment resulted in a 2 × 2 factorial design and the following 4 combinations: HM-CON (n = 7), HM-BCVFA (n = 10), LM-CON (n = 9), and LM-BCVFA (n = 8). On 14 d BEC and 7 DIM an IVGTT was performed following a 1 h fasting period. Baseline blood samples were taken −15 and −5 min before dextrose administration (250 mg/kg BW); blood was then collected at 12 time points over a 3-h time period. Skeletal muscle reserves had no impact on glucose or insulin response across the IVGTT period, whereas BCVFA supplementation increased glucose area under the curve (AUC) in the prepartum period but had no effect in the postpartum period. Prepartum glucose and insulin AUC were higher than the postpartum glucose and insulin AUC. Findings indicate that muscle reserves in the prepartum period do not affect insulin and glucose clearance in periparturient dairy cows, reflecting no differences in insulin sensitivity in response to IVGTT. Changes observed in glucose and insulin AUC between pre- and postpartum IVGTT reflect normal metabolic adaptations to increased energetic requirements of dairy cows between late gestation and early lactation.