Effects of intravenous lipopolysaccharide administration on physiological and ruminal responses that modulate feed intake in beef cattle.

This experiment evaluated feed intake, physiological reactions, and ruminal parameters in beef cattle receiving or not receiving a lipopolysaccharide (LPS) challenge. Ten ruminally-cannulated Angus steers [590 ± 16 kg of body weight (BW)] were housed in individual pens on day -7, ranked by BW, and allocated to 1 of 2 treatments administered intravenously on day 0: 1) 0.5 μg/kg of BW of bacterial LPS (Escherichia coli 0111:B4) diluted in 5 mL of 0.9% sterile saline, or 2) 5 mL of 0.9% physiological saline (CON). Steers had free-choice access to wheat hay, water, and a commercial vitamin + mineral mix (days -7 to 7). Hay dry matter intake (DMI) was evaluated daily from days -5 to 7. Prior to treatment administration on day 0 (hour 0), polyester bags containing 4 g of ground dietary hay (DM basis) were immersed into the rumen of each steer, and incubated for 0, 4, 8, 12, 24, 36, 48, 60, and 72 h for dry matter (DM) and neutral detergent fiber (NDF) degradability evaluation. Steers were also intra-ruminally pulse-dosed with 5 g of Co-EDTA and with Cr-EDTA (0.1 g/kg of BW) prior to treatment administration. Rumen fluid samples were collected at 0, 2, 4, 6, 8, 12, 16, 24, 36, and 48 h, and blood samples were collected at -2, 0, 2, 4, 6, 8, 12, 18, 24, 36, 48, 60, 72, 96, 120, and 144 h relative treatment administration. Values obtained before treatment administration were used as covariates within each respective analysis. Steers receiving LPS had less (P ≤ 0.05) hay DMI on days 0 and 1, less (P < 0.01) rumen liquid volume and dilution rate, and less (P < 0.01) ruminal effective degradability of DM and NDF compared with CON. Steers receiving LPS had greater (P ≤ 0.05) plasma haptoglobin concentration from 18 to 144 h, greater (P ≤ 0.04) plasma cortisol concentration from 2 to 12 h, and less (P ≤ 0.04) total plasma Cr concentration from 2 to 18 h compared with CON. Steers receiving LPS had less (P ≤ 0.03) mean concentrations of acetate, butyrate, valerate, and total volatile fatty acids (VFA) in the rumen fluid compared with CON. Steers receiving LPS had less (P ≤ 0.05) mean total bacterial load in the ruminal fluid, and less mean prevalence of the phyla Spirochaetes and Fibrobacteres and the genera Treponema compared with CON. Results from this experiment suggest that LPS administration elicited host-microbiome endocrine interactions that impaired feed degradability and VFA production in the rumen, particularly a reduction in total bacterial load, which may have contributed to a 48-h decrease in hay DMI.