Infection and inflammation impede efficient animal productivity. The activated immune system ostensibly requires large amounts of energy and nutrients otherwise destined for synthesis of agriculturally relevant products. Accurately determining the immune system's in vivo energy needs is difficult, but a better understanding may facilitate developing nutritional strategies to maximize productivity. The study objective was to estimate immune system glucose requirements following an i.v. lipopolysaccharide (LPS) challenge. Holstein steers (148 ± 9 kg; = 15) were jugular catheterized bilaterally and assigned to 1 of 3 i.v.
Treatments: control (CON; 3 mL saline; = 5), LPS-administered controls (LPS-C; 055:B5; 1.5 mg/kg BW; = 5), and LPS + euglycemic clamp (LPS-Eu; 1.5 mg/kg BW; 50% dextrose infusion to maintain euglycemia; = 5). In LPS-Eu steers, postbolus blood samples were analyzed for glucose every 10 min. Dextrose infusion rates were adjusted to maintain euglycemia for 720 min. All steers were fasted during the challenge. Samples for later analysis were obtained at 180, 360, 540, and 720 min relative to LPS administration. Rectal temperature was increased ∼0.5°C in both LPS treatments relative to CON steers ( = 0.01). Steers in both LPS treatments were hyperglycemic for ∼3 h postbolus; thereafter, blood glucose was markedly decreased (30%; < 0.01) in LPS-C relative to both CON and LPS-Eu steers. A total of 516 ± 65 g of infused glucose was required to maintain continuous euglycemia in LPS-Eu steers. Circulating insulin increased in LPS-C and LPS-Eu steers relative to CON (∼70% and ∼20 fold, respectively; < 0.01). Circulating NEFA increased similarly with time for both CON and LPS-C compared to LPS-Eu steers (∼43%; < 0.01). Plasma L-lactate and LPS binding protein increased (∼198 and ∼90%, respectively; < 0.01) and ionized calcium decreased (18%; < 0.01) in both LPS treatments relative to CON steers. Circulating white blood cells decreased initially in LPS-Eu and LPS-C relative to controls (180 min; 85%) followed by a progressive increase with time ( = 0.02). Blood neutrophils followed the same pattern; however, at 720 min, neutrophils were decreased in LPS-Eu compared to LPS-C, resulting in a decreased neutrophil-to-lymphocyte ratio (54%; = 0.03). The large amount of glucose needed to maintain euglycemia indicates extensive repartitioning of nutrients away from growth and the importance of glucose as a fuel for the immune system.