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Effects of rumen-protected methionine supplementation and bacterial lipopolysaccharide infusion on nitrogen metabolism and hormonal responses of growing beef steers¹

J. W. Waggoner^*,2, C. A. Löest^*,3, C. P. Mathis, D. M. Hallford^* and M. K. Petersen^*

^* Department of Animal and Range Sciences, and Extension Animal Sciences and Natural Resources, New Mexico State University, Las Cruces, NM, 88003

³ Corresponding author: cloest{at}nmsu.edu

Metabolic demand for sulfur-containing AA increases during inflammation in nonruminants. Therefore, Met supplementation may alleviate the negative effects of infection on N balance. Effects of gram-negative bacterial lipopolysaccharide (LPS) and supplemental dietary Met on N balance, serum hormones and haptoglobin, and plasma urea-N and AA were evaluated in 20 Angus-cross steers (BW = 262 ± 6.3 kg). Treatments (2 x 2 factorial) were infusion of no LPS (–LPS) or a prolonged low dose of LPS (+LPS) and dietary supplementation of no (–MET) or 14 g/d (+MET) of rumen-protected Met (providing 7.9 g/d of DL-Met). Steers were adapted to a roughage-based diet (DMI = 1.4% of BW daily) and supplemental Met for 14 d, and were then infused (1 mL/min via intravenous catheter) with LPS on d 1 (2 µg/kg of BW) and 3 (1 µg/kg of BW) of a 5-d collection period. Blood was collected on d 1, before LPS infusion, and at 2, 4, 6, 8, 10, 12, and 24 h after LPS challenge. Diet samples, feed refusals, feces, and urine were collected daily for 5 d. Rectal temperature and serum concentrations of cortisol, prolactin, tumor necrosis factor-, and haptoglobin increased, whereas thyroxine and triiodothyronine decreased for +LPS vs. –LPS steers (LPS x h; P < 0.01). Plasma urea-N was greater for +LPS than –LPS steers (LPS; P = 0.03), and serum IGF-1 was not affected (P 0.26) by LPS or Met. Plasma concentrations of Thr, Lys, Leu, Ile, Phe, Trp, Asn, Glu, and Orn decreased, plasma Ala increased, and Gly and Ser initially increased, then declined in +LPS vs. –LPS steers (LPS x h; P 0.04). Plasma Met was greater for +MET than –MET steers before LPS infusion, but declined in +MET steers after LPS infusion (LPS x Met x h; P < 0.01). By design, DMI was not different, but DM digested was less (P = 0.04) for +LPS than –LPS steers. Infusion of LPS did not affect (P 0.24) N intake, fecal N excretion, or N digested, but resulted in greater (P < 0.01) urinary N excretion and less (P < 0.01) N retention. The absence of an LPS x Met interaction (P = 0.26) for N retention indicates that supplemental Met does not improve the N utilization of growing beef steers exposed to a gram-negative bacterial endotoxin. Decreases in plasma concentrations of several essential AA in +LPS steers suggest that metabolic demand for these AA likely increased in steers exposed to endotoxin.

Key Words: endotoxin challenge • methionine • steer

This article has been cited by other articles:

				J. W. Waggoner, C. A. Loest, J. L. Turner, C. P. Mathis, and D. M. Hallford Effects of dietary protein and bacterial lipopolysaccharide infusion on nitrogen metabolism and hormonal responses of growing beef steers J Anim Sci, November 1, 2009; 87(11): 3656 - 3668. [Abstract] [Full Text] [PDF]