Nutritional modulation of the immune system of beef cattle
Reuter, Richard R.
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Experiments were conducted related to measuring and modulating the acute-phase immune response in beef cattle. In Exp. 1, bacterial lipopolysaccharide (LPS) was administered to 9 steers in doses of 0.5, 1.0, or 2.0 ¦Ìg/kg of body weight (BW) and the resulting serum cortisol concentration and rectal temperature (RT) were measured. Cortisol increased linearly (P = 0.01) with LPS dose, but RT increased independent of dose. In Exp. 2, 2.5 ¦Ìg/kg of BW of LPS was administered to 9 Angus steers. Serum concentrations of cortisol, interleukin (IL)-1¦Â, IL-6, tumor necrosis factor-¦Á (TNF¦Á), interferon-¦Ã (INF¦Ã), and serum amyloid-A (SAA), rectal temperature (RT), ruminal temperature, and respiration and perspiration rates were all increased following LPS challenge (P < 0.10). Rump perspiration rate, IL-4, and IL-2 were not changed (P > 0.24) by LPS challenge. In Exp. 3, a device was developed to automatically monitor RT in cattle. The autonomous device recorded RT at 1-min intervals in cattle in Exp 2. Rectal temperature measured with the device was related (P ¡Ü 0.02 ) to IL-6 and TNF¦Á concentration following LPS challenge. In Exp 4, two non-nutritive feed additives (Sucram, an artificial sweetener; Omni-GenAF, an immunomodulatory yeast product) were fed to newly received heifers for 44 d. Overall health and growth performance of the cattle were better than expected for heifers of the type and background used, and feed additives had no effect on growth, intake, or health. Nonetheless, the combination of Sucram and Omni-Gen AF decreased haptoglobin concentration on d 16 (P = 0.001). Deleterious effects of the additives on marbling score were evident (P = 0.05), and a long feeding period, relatively free of handling stress, mitigated negative effects of animal temperament on performance. In Exp 5, 70% and 30% concentrate diets were fed ad libitum to beef steers for 28 d (70AL and 30AL, respectively) to test the effects of energy source and energy intake on immune response. A third dietary treatment (70RES) consisted of the 70% fed in an amount restricted to equal the net energy for gain (NEg) intake of the 30AL treatment. Two days before an LPS challenge, 4 steers in each diet treatment were injected with tilmicosin phosphate (1 mL/30 kg of BW), and 4 steers were injected with an equal volume of saline. Steers were catheterized in the jugular vein and then challenged with 2.0 ¦Ìg LPS /kg of BW. Both energy source and energy intake affected the pro-inflammatory immune response; the 30% concentrate diet increased (P ¡Ü 0.05) TNF¦Á and INF¦Ã response to LPS compared with the 70% concentrate diet, and 70RES increased IL-6 (P = 0.003) response compared with 70AL. Tilmicosin accelerated the febrile response (P = 0.01) across all diets, and tilmicosin interacted with energy intake to increase pre-challenge levels of TNF¦Á, INF¦Ã, and IL-6, and SAA response to the challenge, in 70RES compared with 70AL (P ¡Ü 0.05). Nutrition and management practices have immunomodulatory effects in beef cattle. More precisely measuring the acute-phase response, and correlating responses to challenge models with clinical health performance in commercial environments will help researchers make more effective recommendations to cattle producers. Benefits to animals, producers, and the public can be realized when nutrition and management are effectively used to decrease morbidity in beef cattle.