Metabolic and inflammatory response to an early lactation intravenous lipopolysaccharide challenge in Holstein cows fed differing levels of metabolizable protein during the transition period

The nadir in transition cow nutrient balance coincides with a period of heightened inflammation. Decreased circulating AA might contribute to an altered immune phenotype that favors a proinflammatory response. Objectives were to (1) investigate the effect of increasing MP supply in the prepartum, postpartum, or both diets on the response to an intravenous (IV) LPS challenge, (2) compare the response of IV LPS to fasted unstimulated control cows, and (3) determine the duration of the effect of IV LPS or fasting on milk production. Multiparous cows (n = 96) were assigned to 1 of 4 treatment groups at 28 d before expected calving following a randomized block design. Prepartum diets were formulated to contain either a control (85 g of MP/kg of DM) or high (113 g of MP/kg of DM) level of MP. Postpartum diets were formulated to contain either a control (104 g of MP/kg of DM) or high (131 g of MP/kg of DM) level of MP. To control the potential confounding effects of Met and Lys supply, diets were formulated to supply an equal amount at 1.24 and 3.84 g/Mcal of ME in both prepartum diets and 1.15 and 3.16 g/Mcal of ME in both postpartum diets, respectively. The combination of a pre- and postpartum diet resulted in 4 treatment groups: control-control, control-high, high-control, and high-high. Cows (n = 24; 23 ± 2 DIM) were selected to undergo an IV LPS challenge (0.0625 µg/kg of BW over 1 h; IVLPS) in 6 blocks. Each block included 1 cow from each treatment and 1 unchallenged control cow (n = 6; DIM = 22 ± 2; CON) alternating between treatments. All cows were allowed 1 h of ad libitum feed intake before IV LPS and fasted for 10 h following challenge. Separate repeated measure ANOVA models were used to compare the effects of dietary treatment and IV LPS. Dietary treatment did not affect the clinical, inflammatory, or hematologic response to IV LPS. Compared with baseline values, DMI and milk yield decreased on the day of challenge 14.0% and 17.7% in IVLPS and 13.8% and 4.0% in CON, respectively. Compared with CON, IVLPS decreased leukocyte counts at 1 and 4 h and increased tumor necrosis factor from 1 to 4 h, IL-10 from 1 to 6 h, and haptoglobin from 24 to 72 h. Intravenous LPS increased concentrations of glucose at 10 h and decreased those of BHB at 10 h, fatty acid at 6 and 10 h, and calcium from 3 to 10 h relative to challenge. Intravenous LPS decreased circulating EAA from 2 to 8 h and NEAA at 4 h relative to challenge. Fasting and IVLPS decreased milk yield on the day of challenge compared with cows from the source population but milk recovered by d 2 relative to challenge. In conclusion, MP supply did not modify the inflammatory response to IV LPS, but IV LPS altered the metabolic response compared with CON. Furthermore, fasted and IV LPS-challenged animals recovered milk production within 2 d postchallenge.