THE EFFECT OF DIETARY LIPOIC ACID ON METABOLIC HORMONES AND ACUTE PHASE PROTEINS IN STEERS CHALLENGED WITH INFECTIOUS BOVINE RHINOTRACHEITIS

Authors: SCHMIDT, TY - UNIVERSITY OF MISSOURI; BERG, ERIC - UNIVERSITY OF MISSOURI; LARSON, ROBERT - UNIVERSITY OF MISSOURI; KLEIBOEKER, STEVE - UNIVERSITY OF MISSOURI; OLSON, K - UNIVERSITY OF MISSOURI; KEISLER, DUANE - UNIVERSITY OF MISSOURI; Carroll, Jeffery - Jeff Carroll; BROWN, MIKE - WEST TEXAS A&M UNIVERSITY

Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2005
Publication Date: 7/15/2006
Citation: Schmidt, T.B., Brown, M.S., Larson, R.L., Kleiboeker, S.B., Olson, K.C., Keisler, D., Carroll, J.A., Berg, E.P. 2006. Effect of dietary lipoic acid on metabolic hormones and acute-phase proteins during challenge with infectious bovine rhinotracheitis virus in cattle. American Journal of Veterinary Research. 67(7):1192-1198.

Interpretive Summary: Bovine respiratory disease (BRD) is responsible for over 75% of feedlot morbidity and 50% of feedlot mortality making it the most economically important disease affecting U.S. growing and finishing cattle. To date, there is no information about lipoic acid in regards to its affect on the devastating effects of BRD. Lipoic acid is a powerful antioxidant capable of systematically scavenging a number of known cell-damaging free radicals and is both fat and water soluble. It is readily absorbed into the cell where it is converted to its oxidized form, dyhydrolipoic acid, which is capable of regeneration of vitamin E, vitamin C, and glutathione peroxidase, three of the primary antioxidants present within the living system. Lipoic acid has been reported to inhibit the transcription factor NF-kB which is involved in toxic over stimulation of the inflammatory response system. Therefore, the objective of this study was to determine the effect of dietary lipoic acid supplementation on infectious bovine rhinotracheitis virus (IBRV) challenged feeder steers and the subsequent effect on metabolic hormones and acute phase proteins. Crossbred steers (n=32) were randomly assigned to four treatments: control (CON; no lipoic acid, IBRV challenge), 16 mg of lipoic acid/kg of body weight + IBRV challenge (LA16), 32 mg of lipoic acid/kg of body weight + IBRV challenge (LA32), and negative control (NC; no lipoic acid, no IBRV challenge). Steers were acclimated to diet, treatment (lipoic acid dietary supplementation), and environment for 21 d. Immediately following the 21 d adaptation period, CON, LA16, and LA32 steers received an intranasal dose of IBRV. Blood samples, nasal swabs, body weight, and rectal temperatures were collected on 0, 1, 3, 5, 7, 14, and 21 d post-dosing. Results indicate that supplementation of lipoic acid at 32 mg/kg of body weight appears to augment certain aspects of immune function of steers during an IBRV challenge. Steers fed lipoic acid at 32 mg/kg of body weight recovered from the IBRV challenge more quickly in terms of body weight gain and dry matter intake relative to IBRV-challenged steers fed no lipoic acid or lipoic acid at 16 mg/kg of body weight. The IBRV challenge appeared to reduce dry matter intake to a greater degree than water intake; however, supplementation with lipoic acid at 32 mg/kg body weight appeared to moderate this reduction in dry matter intake. The various indices of the severity and duration of BRD symptoms that were recorded during this trial (e.g., clinical illness scores, rectal temperatures, and serum acute phase proteins) were interpreted to suggest that the IBRV challenge technique used in this study was successful in causing clinical symptoms of BRD; however, most clinical signs of BRD persisted for fewer than 10 d and none appeared to be severe. Future research must evaluate and confirm the role of lipoic acid supplementation to feedlot cattle experiencing BRD symptoms of greater magnitude.

Technical Abstract: Crossbred steers challenged with infectious bovine rhinotracheitis virus (IBRV) were used to determine the effect of supplemental lipoic acid (LA) on circulating metabolic hormones and acute phase proteins. Steers (n = 32; BW = 260 + or - 6 kg) were randomly assigned to four treatments: control (CON; no LA, IBRV challenge), 16 mg of LA/kg of BW + IBRV challenge (LA16), 32 mg of LA/kg of BW + IBRV challenge (LA32), and negative control (NC; no LA, no IBRV challenge). Steers were acclimated to diet, treatment (LA dietary supplementation), and environment for 21 d. Immediately following the 21 d adaptation period, CON, LA16, and LA32 steers received an intranasal dose of IBRV (Cooper stain, 1 - 10 million PFU; 2 ml/nostril); NC received 2 mL of saline/nostril. Blood samples, nasal swabs, BW, and rectal temperatures were collected on 0, 1, 3, 5, 7, 14, and 21 d post-dosing. Daily DMI was recorded. Blood serum was analyzed for haptoglobin, amyloid-A, leptin, and serum-neutralization titer concentration. Prior to the IBRV challenge, DMI was similar (P = 0.20) among treatments. Seven d post-dosing, DMI was higher (P < 0.001) for LA32 steers compared to CON and LA16 steers, but lower than NC steers. All treatment groups experienced BW loss during the first 5 d post-challenge. Steers fed LA32 began gaining BW by d 7 post-dosing, whereas BW of CON and LA16 steers continued to decline. Serum haptoglobin concentrations were similar (P = 0.77) among treatments before the IBRV challenge. On d 5, LA32 steers had lower (P = 0.04) serum haptoglobin than CON steers. Serum haptoglobin of LA32 steers was lower (P = 0.001) than CON and LA16 steers on d 7. Serum haptoglobin concentrations for all treatments were at or below pre-challenge concentrations by d 14. Serum-neutralization titers for 30 of 32 steers were negative for IBRV antibodies before the viral challenge; however, all steers, including those on the NC treatment, were positive for IBRV antibodies 21 d after viral dosing. Although all steers contracted IBRV, steers supplemented 32 mg/kg BW of LA had a more rapid recovery (less than or equal to 7d post inoculation).