Effect of vitamin E source, natural versus synthetic, and quantity on serum and tissue alpha-tocopherol concentrations in finishing swine.

Relative vitamin E status of pigs fed natural or synthetic vitamin E was evaluated based on serum and tissue alpha-tocopherol concentrations. Individually fed finishing gilts at a BW of 70.5 kg (n = 24) were allotted to dietary treatments based on initial BW. The 5 dietary treatments consisted of a positive control diet using synthetic vitamin E acetate (Syn E Ac) supplemented at 22 mg/kg, and 4 dietary levels of natural vitamin E acetate (Nat E Ac) supplemented at 6.71, 8.33, 11.00, and 16.18 mg/kg of diet. Before initiation of the 32-d experiment, pigs were fed a non-vitamin E-fortified diet for 30 d. Diets were formulated to contain true ileal digestible lysine of 0.9 and 0.8% for the pretest and test diets. Serum samples were collected on d 15 and 32, whereas tissue samples were collected on d 32 for alpha-tocopherol analysis. Serum alpha-tocopherol concentrations on d 15 and 32 were greater (P < 0.05) in pigs fed 8.33, 11.00, or 16.18 mg/kg of Nat E Ac than in pigs fed 22 mg/kg of Syn E Ac. When compared with pigs fed 22 mg/kg of Syn E Ac, alpha-tocopherol concentrations were greater (P < 0.05) in 6 tissues (heart, kidney, spleen, liver, lung, and adipose) in pigs fed 16.18 mg/kg of Nat E Ac; greater (P < 0.05) in heart, kidney, spleen, liver, and adipose tissue in pigs fed 11.00 mg/kg of Nat E Ac; and greater (P < 0.05) in spleen, loin, and adipose tissue in pigs fed 8.33 mg/kg of Nat E Ac. As dietary Nat E Ac increased from 6.71 to 16.18 mg/kg, serum alpha-tocopherol increased linearly (P < 0.01) on d 15 and 32 of the experiment. Increasing dietary Nat E Ac linearly increased (P < 0.05) alpha-tocopherol concentrations for lung, heart, kidney, spleen, and liver. These results indicate that Nat E Ac was an effective vitamin E source and its relative bioavailability was substantially greater than 1.36 for finishing swine when compared with Syn E Ac.

Bioavailability of threonine in soybean meal for young pigs.

The bioavailability of threonine in solvent-extracted soybean meal for 10- to 20-kg pigs was determined using the slope-ratio method. In Exp. 1, the assay range was determined by feeding six diets to 144 pigs. The basal diet (.40% threonine) contained corn, soybean meal, and corn gluten meal. Five additional diets were formulated by supplementing the basal diet with .05 to .25% crystalline L-threonine in .05% increments. Weight gain, gain/feed, and plasma concentrations of threonine and urea responded quadratically (P < .05) to increasing dietary threonine. Breakpoints ranged from .51 to .54% dietary threonine. Experiment 2 consisted of seven trials in which a total of 239 pigs were used in a randomized complete block design. Pigs were penned individually and had ad libitum access to feed and water during the 21-d experiment. The same basal diet that was used in Exp. 1 was supplemented with .018, .053, or .070% threonine from either L-threonine or soybean meal. The weight gains of the pigs were partitioned to yield the response due to the supplemental threonine ingested. Multiple regression was performed on partitioned weight gain vs supplemental threonine intake, and the assay was tested for validity. The regression lines for L-threonine and soybean meal were linear (P < .05) and the intercepts were not significantly different (P > .10). The slope ratio for soybean meal:L-threonine was .80. Although the difference between the soybean meal and L-threonine slopes was not significant (P > .23), the best estimate of the bioavailability of threonine in soybean meal relative to that of L-threonine was 80%.

Bioavailability of threonine in soybean meal for rats and chicks.

The bioavailability of threonine in soybean meal and the effects of the excess amino acids in soybean meal on the estimate were measured using rats and chicks in slope-ratio assays. In Exp. 1, a corn-based diet containing .23% threonine was supplemented with 0 to 45% L-threonine in .05% increments. The growth rate of weanling rats fed these diets increased quadratically (P less than .001) with L-threonine addition, the increase being essentially linear up to the .10% addition. In Exp. 2, the basal diet was supplemented with 0, .025, .050, .075, or 100% threonine from L-threonine, simulated soybean meal (a mixture of crystalline amino acids with a pattern designed to simulate soybean meal), or soybean meal. Regressions of partitioned weight gain and body N gain of rats vs supplemental threonine intake were calculated for each source using multiple regression. Slope ratios (soybean meal:L-threonine) were .91 for weight gain and .92 for body N gain. The additional amino acids in simulated soybean meal did not affect the estimate. For Exp. 3, a corn-soybean meal-based diet containing .48% threonine was supplemented with 0 to 60% L-threonine in .10% increments. The growth rate of broiler chicks fed the diets increased quadratically (P less than .001) with L-threonine addition. The increase was essentially linear up to the .10% addition. In Exp. 4, the basal diet was supplemented as in Exp. 2. Regressions of partitioned weight gain of chicks vs supplemental threonine intake were calculated for each source. The slope ratio for soybean meal:L-threonine was 1.03; however, the model exhibited fundamental invalidity and therefore the estimate should be interpreted with caution. The additional amino acids in the simulated soybean meal did not affect the value.