Chromium and palmitic acid supplementation modulate adipose tissue insulin sensitivity in postpartum dairy cows

Periparturient dairy cows exhibit intense lipolysis driven by reduced DMI, enhanced energy needs, and the loss of adipose tissue (AT) insulin sensitivity. Extended periods of low insulin sensitivity and negative energy balance induce lipolysis dysregulation, leading to increased disease susceptibility and poor lactation performance. Chromium (Cr) supplementation improves systemic insulin sensitivity, whereas palmitic acid (PA) increases energy availability for milk production. However, the effect of supplementing Cr and PA alone or in combination on insulin sensitivity in AT is unknown. A total of 32 multiparous cows were used in a randomized complete block design experiment and randomly assigned to one of 4 diets fed from 1 to 24 DIM: a control diet with no supplementation (CON, n = 8); the Cr diet (Cr propionate at 0.45 mg/kg Cr/kg DM, n = 8); the PA diet (1.5% DM, n = 8); or Cr+PA (n = 8). Plasma samples were collected at -13 ± 5.1 d prepartum (PreP), and at 14.4 ± 1.9 d (PP1) and 21 ± 1.9 d (PP2) after calving for quantification of albumin, BHB, BUN, calcium, cholesterol, glucose, nonesterified fatty acids (NEFA), total protein, iron, transferrin, triglycerides, and oxylipids. Subcutaneous AT (SCAT) explants were collected at PreP, PP1, and PP2 and incubated in the presence of the lipolytic agent isoproterenol (ISO = 1 µM, BAS = 0 µM) for 3 h. The antilipolytic effect of insulin (1 µL/L) on SCAT explants was evaluated during ISO stimulation (ISO+INS). Lipolysis was quantified by glycerol release in the medium (nmol glycerol/mg AT). Macrophage infiltration and adipocyte size were measured using hematoxylin and eosin-stained AT sections and immunohistochemistry. The Cr diet tended to reduce postpartum NEFA concentrations when compared with CON, PA, and Cr+PA. Likewise, Cr increased the percentage of large adipocytes (>9,000 µm²) postpartum compared with other diets. In line with higher lipid content, Cr-fed cows had higher ex vivo BAS lipolysis at PP2 when compared with PA and Cr+PA. Isoproterenol induced higher lipolysis at PP1 and PP2, but it was not affected by Cr and PA. The ISO+INS treatment reduced lipolysis by 29.91% ± 11% in Cr compared with ISO. In contrast, ISO+INS did not affect ISO lipolysis in CON, PA, and Cr+PA. Plasma transferrin was reduced by Cr. At PP2, PA cows had 3.3-fold higher macrophage infiltration in SCAT when compared with CON and Cr. Plasma 9-hydroxyoctadecadienoic acid (HODE) and 9-oxo-octadecadienoic acid (oxoODE) were increased by Cr+PA. Palmitic acid increased plasma 13-oxoODE and Cr increased the ratio of 13-HODE to 13-oxoODE. Palmitic acid increased 5-iso prostaglandin F_2α-VI. Our results demonstrate that supplementing Cr during the immediate postpartum enhances SCAT insulin sensitivity and lipid accumulation. Further studies should determine the effects and mechanisms of action of Cr and PA on AT lipogenesis, adipogenesis, and their impact on lactation performance.