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Balance and serum concentration of biotin in sheep fed alfalfa meal-based diets with increasing level of concentrate.

The objective of this study was to test the hypothesis that serum biotin concentration and biotin balance (consumed - [urinary output + fecal output]) measured as total avidin-binding substances (biotin + biotin metabolites) are responsive to changes in the proportions of dietary alfalfa meal and concentrate fed to sheep. Eight sheep (initial BW = 40 kg) consumed a pelleted alfalfa meal-based diet that had 95:5, 48:52, 23:77, or 9:91% alfalfa meal:concentrate ratios (DM basis) in a replicated 4 x 4 Latin square design with 20-d periods (10 d of acclimation, 7 d of adaptation, and a 3-d collection period with jugular blood drawn on the last day). Replacing alfalfa meal with concentrate in the pelleted diets decreased dietary concentrations of biotin proportionally. As the percentage of alfalfa meal in the diet decreased, there was a linear decrease in daily DM intake (1,128 to 901 g of DMI/d; P < 0.01), with a linear (P < 0.01) and quadratic (P < 0.01) increase in the apparent total-tract DM digestibility of diets (51.0 to 80.0%). The biotin consumed decreased with alfalfa meal proportion in the diet (linear, P < 0.01). Both fecal biotin concentration (linear, P < 0.01) and fecal biotin output (quadratic, P < 0.05) increased, reaching peaks at 23% alfalfa meal. Fecal biotin output was not correlated with biotin intake, DMI, or intake of digestible DM. Mean urinary output, urinary biotin concentration, urinary biotin output, and serum biotin concentration were not affected by treatments. Means of biotin balance were negative and revealed the same trends among treatments as did fecal output. Biotin balance was a quadratic (P < 0.05) function of decreasing alfalfa meal in the diet, with more negative values at the alfalfa meal:concentrate ratio of 23:77. Results suggest that the greatest synthesis of biotin in the total digestive tract occurs with diets of either 52 or 77% concentrate for sheep; however, research addressing the significance of biotin metabolites on biotin balance and plasma biotin pool is needed.