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Two experiments were conducted to refine the Ile needs in 7- to 11-kg pigs. In Exp. 1, 1,680 pigs were fed a 1.25% digestible Lys diet containing 7.5% spray-dried blood cells (as-fed basis) with supplemental crystalline Ile (0.06% increments) to generate seven levels of apparent digestible Ile (0.47 to 0.83%). There were 12 replicates of each treatment with 20 pigs per pen, and treatments were imposed at an initial BW of 7 kg and continued for 16 d. Responses in ADG, ADFI, G:F, and plasma urea nitrogen (PUN) were quadratic (P < 0.01) over the 16-d period. Data were fitted to both a single-slope broken line and a quadratic fit, and when the quadratic response curve was superimposed on the broken line, the points at which the quadratic curve first intersected the plateau of the broken line occurred at 0.70, 0.73, 0.66, and 0.65% digestible Ile for ADG, ADFI, G:F, and PUN, respectively. Using the ADG and ADFI obtained at this intersection point resulted in an estimate of 9.1 mg of digestible Ile per gram of weight gain. In Exp. 2, 1,840 pigs were fed similarly composed diets, except that digestible Lys was lowered in six diets to 1.10% by decreasing soybean meal. Crystalline Ile was supplemented at 0.09% increments to generate six levels of digestible Ile (0.37 to 0.83%). A seventh diet contained 1.25% digestible Lys by supplementing the 0.83% digestible Ile diet with 0.19% L-Lys HCl to verify that 1.10% digestible Lys was deficient for these pigs. There were 12 replicates of each treatment with 22 pigs per pen, and treatments imposed at an initial BW of 7 kg and continued for 16 d. Supplementation of Lys to the 0.83% digestible Ile diet (1.10 vs. 1.25% digestible Lys) did not affect ADG (260 vs. 264 g/d, P = 0.60) and ADFI (359 vs. 343 g/d, P = 0.20), whereas G:F (725 vs. 774 g/kg, P < 0.01) was improved by increasing dietary Lys. Responses in ADG, ADFI, and G:F to the first six diets were quadratic (P < 0.01) over the 16-d period. The points at which the quadratic curve first intersected the plateau of the broken line occurred at 0.686, 0.638, and 0.684% digestible Ile for ADG, ADFI, and G:F, respectively. Using the ADG and ADFI obtained at this intersection point results in an estimate of 9.9 mg of digestible Ile per gram of weight gain. These results suggest that although the percent digestible Ile requirement and digestible Ile:Lys ratio for starter (7 to 11 kg) pigs may be higher than 1998 NRC recommendations, the requirement may be lower than current recommendations when taking gain and feed intake into account.

Nine crossbred gilts were surgically fitted with indwelling anterior vena cava cannulae, and randomly assigned to receive intramuscular injections of either 2.2 micrograms biotin/kg body wt, 6.6 micrograms biotin/kg body wt or a sham dose of carrier medium. Plasma biotin concentrations (PBC) were determined from blood samples taken at 39 time points during a 73 h period. There were no time differences (P less than .05) in PBC for the sham injected gilts suggesting no diurnal variation in PBC. The sham injected gilts had an overall mean PBC of 42.5 ng/dl. Following biotin injection, PBC increased and peaked at 4 h (66.7 ng/dl) and 6 h (90.9 ng/dl), respectively for gilts receiving low and high levels of biotin. These increases in PBC resulted in treatment differences (P less than .05) in PBC from 4 h to 10 h post-injection. Biotin uptake and clearance rates were calculated using exponential curves. Uptake rates (% increase PBC/h) were 16.5 and 15.9% and clearance rates (% decrease PBC/h) were 5.7 and 2.8%, respectively, for gilts receiving low and high levels of biotin. Clearance rate, expressed as the amount of biotin cleared per hour, was similar (2 to 3 ng/dl) for both biotin treatments.