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Influence of Dietary Manganese on Performance, Lipid
Metabolism, and Carcass Composition of Growing and Finishing Steers L. R. Legleiter, J. W. Spears, and K. E. Lloyd Summary Dietary manganese (Mn) did not affect cattle performance. Increasing dietary Mn increased tissue Mn concentrations, longissimus muscle lipid concentration and decreased serum non-esterified fatty acid (NEFA) concentrations. Supplementing physiological or pharmacological concentrations of Mn did affect lipid metabolism, however, this did not result in altered carcass characteristics. Introduction The Mn requirement for growing cattle is listed as 20 mg Mn/kg DM and is based on limited research. To our knowledge the requirement for Mn has not been evaluated for growing or finishing steers in confinement. Additionally, little research has focused on the biological role(s) of Mn in cattle. Manganese has been shown to influence lipid metabolism in several studies using mice and rats as models. Baly et al. (1990) demonstrated that isolated adipocytes from Mn deficient rats had decreased uptake of glucose, decreased insulin receptors, and decreased triglyceride synthesis compared to rats fed adequate Mn. High dietary Mn has been shown to mimic insulin and increase glucose uptake by isolated rat adipocytes (Baquer et al., 2003). Smith and Crouse (1984) established that intramuscular (IM) fat preferentially utilizes glucose as an acetyl unit precursor for lipogenesis in cattle. The present study was conducted to evaluate the effect of dietary Mn on performance and tissue Mn concentrations of growing and finishing steers. Additionally, the effects of physiological and pharmacological levels of Mn on lipid metabolism, and subsequent carcass characteristics and quality were evaluated.
Materials and Methods One hundred twenty Angus cross steers (248 kg) were blocked by body weight and source of origin, and randomly assigned to one of six treatments. Treatments consisted of control (no supplemental Mn), 10, 20, 30, 120 or 240 mg supplemental Mn/kg DM. Supplemental Mn was provided from MnSO4·H2O. Steers were fed a corn silage-based diet in the growing phase (84 d) and a corn-based diet during the finishing phase (120 d). The basal diets had 29.2 and 8.1 mg Mn/kg DM in the growing and finishing diets, respectively. All steers were weighed every 28 d and jugular blood samples were collected on d 56 of both the growing and finishing phase. Steers were slaughtered by weight block after reaching an average finishing weight of 550 kg. Hot carcass weights were recorded and liver samples collected immediately after slaughter. Fat depth over the longissimus muscle(LM), estimated percentage kidney, pelvic, and heart fat, LM area, bone maturity, marbling score, and USDA yield grade and quality grade were determined by a certified USDA grader 48 h after slaughter. After carcass grading a LM sample was taken from the right side of each carcass. Plasma, liver and LM were all analyzed for Mn concentration. Plasma glucose and serum NEFA concentrations were also determined. Longissimus muscle samples were analyzed for total lipid content.
Results and Discussion Dietary Mn did not affect animal performance indicating current recommended requirements for Mn are adequate. Additionally, the supplemental Mn concentrations considered pharmacological did not negatively affect performance during the growing or finishing phase. Plasma Mn concentrations in the growing and finishing phases were not affected by dietary Mn concentration, however, liver and LM Mn concentrations increased linearly with increasing dietary Mn (Table 1). Plasma glucose concentrations were not affected by dietary Mn during the growing or finishing phases (Table 1). Serum NEFA tended to decrease linearly as supplemental Mn increased from 0 to 240 mg/kg DM in the finishing phase. This suggests that increasing dietary Mn may have decreased lipolysis or increased uptake of NEFA from blood. Carcass characteristics were not affected by treatment (Table 2). Muscle lipid content tended to behave in a quadratic fashion, however, this did not translate into altered carcass quality, as marbling scores and quality grades were similar across treatments. Combining the concepts of Mn increasing the uptake of glucose by isolated adipocytes, and IM adipocytes preferentially utilizing glucose, the potential for dietary Mn in the physiological or pharmacological range to increase IM fat seemed plausible. The trend for decreased NEFA concentrations and increased LM lipid content with a concomitant increase in liver and LM Mn concentrations suggest that lipid metabolism was affected by dietary Mn. However, the Mn induced changes in lipid metabolism did not result in alterations in carcass characteristics. It is likely the in vitro Mn concentrations required to achieve insulin-like effects in isolated rat adipocytes are greater than peripheral Mn concentrations achieved in our study. Implications Current Mn requirements for growing and finishing steers appear to be adequate. Although supplementing Mn at pharmacological levels appears to affect lipid metabolism, this affect does not result in improved carcass quality. References Baly, D. L., J. S. Schneiderman, and A. L. Garcia-Welsh. 1990. Effect of manganese deficiency on insulin binding, glucose transport and metabolism in rat adipocytes. J. Nutr. 120:1075-1079. Baquer, N. Z., M. Sinclair, S. Kunjara, U. Yadav, and P. McLean. 2003. Regulation of glucose utilization and lipogenesis in adipose tissue of diabetic and fat fed animals: Effects of insulin and manganese. J. Biosci. 28:215-221. Smith, S. B. and J. D. Crouse. 1984. Relative contributions of acetate, lactate and glucose to lipogenesis in bovine intramuscular and subcutaneous adipose tissue. J. Nutr. 114:792-800. Table 1. Effects of dietary Mn on plasma and tissue Mn and blood metabolites
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