Three experiments were conducted to study the effects of extrusion processing on growth performance of weanling pigs. In Exp. 1, 350 weanling pigs (initially 4.4 +/- 1.0 kg BW and 10 +/- 2 d of age) were used to study the effects of various carbohydrate sources (corn, cornstarch, broken rice, wheat flour, and grain sorghum), with or without moist extrusion processing, on growth performance in a 5 x 2 factorial arrangement of treatments. No carbohydrate source x extrusion processing interactions were observed (P > .10). Growth performance was not affected by extrusion processing; however, pigs fed corn had poorer growth performance (P < .05) than those fed other carbohydrate sources. In Exp. 2, 360 weanling pigs (initially 5.0 +/- .5 kg BW and 10 +/- 2 d of age) were used to determine the interactive effects of ingredient processing and diet complexity on growth performance. Three processing combinations were used with either a simple or complex diet formulation in a 3 x 2 factorial arrangement of treatments. The three processing conditions were 1) pelleted only (control); 2) corn that was moist-extruded and then the complete diet was pelleted (extruded); or 3) the complete diet was expanded and then pelleted (expanded). Pigs fed extruded diets had a greater improvement in ADG as diet complexity increased than those fed other diets (processing x diet complexity interaction, P < .10). Pigs fed moist-extruded corn had the best growth performance (P < .01). In Exp. 3, 210 weanling pigs (initially 6.8 +/- 1.5 kg BW and 21 +/- 2 d of age) were fed pelleted diets containing nonextruded corn (14.5% gelatinization; control) or corn extruded to provide 38.7, 52.7, 64.4, or 89.3% gelatinization. Average daily gain and ADFI decreased and then increased (P < .05), but apparent digestibility of DM, CP, and energy (P < .01) increased and then decreased with increasing gelatinization. These results indicate that moist extrusion processing of carbohydrate sources has variable effects on growth performance of early-weaned pigs and that the degree of gelatinization does not seem to be a major factor in explaining this variation.

Three experiments were conducted to determine the effects of omitting vitamin and trace mineral premixes and(or) reducing inorganic phosphorus additions to finishing diets on growth performance, carcass characteristics, and muscle quality in pigs. In Exp. 1, a corn-soybean meal-based diet (.70% lysine, .65% Ca, and .55% P) was used as the control. Pigs (n = 128; average initial BW of 85.7 kg) were fed the control diet or the control diet without 1) the vitamin premix, 2) the trace mineral premix, or 3) both premixes. Omitting the premixes had no effect on ADG (P>.39); gain/feed (P>.17); carcass backfat thickness (P>.42); and marbling, color, and firmness of the longissimus muscle (P>.11). In Exp. 2, pigs (n = 128; average initial BW of 86.2 kg) were fed the control diet (.65% Ca and .53% P) used in Exp. 1 and the control diet without 1/3 (.56% Ca and .46% P), 2/3 (.51% Ca and .40% P), or all (.47% Ca and .31% P) of the added monocalcium phosphate (MCP). Omitting up to 2/3 of the MCP increased ADG (quadratic effect, P<.02) and had no effect on meat quality (P>.12), but backfat thickness increased slightly (quadratic effect, P<.02). In Exp. 3, pigs (n = 160; average initial BW of 86.6 kg) were fed the control diet used in Exp. 1 or the control without 1) the vitamin and trace mineral premixes, 2) 2/3 of the MCP, or 3) the premixes and 2/3 of the MCP. Treatment had no effects on ADG (P>.23), gain/feed (P>.94), stomach lesions (P>.37), or serum gamma globulins (P>.08). In conclusion, vitamin and trace mineral premixes and up to 2/3 of the supplemental MCP can be omitted during late finishing (i.e., approximately the final 30 d) to reduce nutrient excesses that increase cost of feeding and nutrients excreted in waste material.

We conducted two experiments evaluating the lysine requirement of 91- to 113-kg gilts. Gilts (PIC L326 x C-22) with initial body weights of 42 (Exp. 1) or 39 kg (Exp. 2) were blocked by weight in a randomized complete block design. Experiment 1 included 105 gilts, with seven gilts per pen and five replications (pens) per treatment. Experiment 2 included 125 gilts, with eight gilts per pen and four replications (pens) per treatment. Gilts were fed a corn-soybean meal diet (no crystalline lysine) containing 1.0% total lysine from 39 to 68 kg and .80% total lysine from 68 to 91 kg. In Exp. 1, when the average weight of gilts within a block reached 91 kg, gilts were fed corn-soybean meal diets containing .40, .55, or .70% total lysine. Increasing dietary lysine increased (linear, P < .05) ADG, daily lysine intake (11.3, 15.1, and 19.8 g/d), gain/feed, plasma urea N, and carcass lean percentage but decreased 10th rib fat depth. Because of the linear responses in Exp. 1, Exp. 2 was conducted with corn-soybean meal diets containing .60, .70, .80, or .90% total lysine. Increasing total dietary lysine had no effect on ADG, gain/feed, 10th rib fat depth, or carcass lean percentage (P > .10). Daily lysine intake increased (linear, P < .01) with increasing dietary lysine (18.1, 21.1, 23.9, 26.5 g/d). Based on these results, the total dietary lysine requirement for 91- to 113-kg gilts is approximately .60% total lysine, which corresponds to approximately 18 g/d lysine intake.

We conducted three experiments to determine the sulfur amino acid (SAA) and methionine requirements of finishing gilts. Gilts (PIC Line 326 x C-15, Exp. 1; Line 326 x C-22, Exp. 2 and 3) were blocked by initial weight in randomized complete block designs. In Exp. 1, 64 gilts (initially 54 kg) were fed diets containing either .56 or .44% apparent digestible lysine with increasing SAA levels (63, 70, and 77% of apparent digestible lysine) in a 2 x 3 factorial. A lysine x SAA interaction (P < .10) was observed for ADG and ADFI. Increasing SAA:lysine ratios from 63 to 70% in diets containing .56% apparent digestible lysine increased ADG and ADFI; however, increasing the SAA:lysine ratio in diets containing .44% apparent digestible lysine decreased ADG and ADFI. Pigs fed .56% apparent digestible lysine had higher (P < .05) ADG and gain:feed ratio (G/F) and lower 10th rib fat depth than pigs fed .44% apparent digestible lysine. Increasing the SAA:lysine ratio had no effect on G/F or carcass characteristics. In Exp. 2, 80 gilts (initially 74 kg) were fed diets containing .225, .25, .275, .30, or .325% apparent digestible SAA (45, 50, 55, 60, or 65% of .50% apparent digestible lysine, respectively). Increasing SAA concentrations decreased ADG and G/F (linear, P < .06). In Exp. 3, 105 gilts (initially 72 kg) were fed diets containing .20% apparent digestible cystine and .10, .125, or .15% apparent digestible methionine (20, 25, or 30% of .50% apparent digestible lysine). Increasing digestible methionine increased ADG, ADFI, plasma methionine concentrations (linear, P < .01), and G/F (quadratic, P < .03). The greatest increases in ADG and G/F were observed when apparent digestible methionine was increased from .10 to .125%. Based on these results, the apparent digestible methionine requirement is no greater than 25% of apparent digestible lysine, in diets containing excess cystine. This equates to an apparent digestible SAA:lysine ratio that is no greater than 50%.