Two experiments were conducted to determine the effects of feeding reduced-CP, AA-supplemented diets at two ambient temperatures (Exp. 1) or three levels of dietary NE (Exp. 2) on pig performance and carcass composition. In Exp. 1, 240 mixed-sex pigs were used to test whether projected differences in heat increment associated with diet composition affect pig performance. There were 10 replications of each treatment with four pigs per pen. For the 28-d trial, average initial and final BW were 28.7 kg and 47.5 kg, respectively. Pigs were maintained in a thermoneutral (23 degrees C) or heat-stressed (33 degrees C) environment and fed a 16% CP diet, a 12% CP diet, or a 12% CP diet supplemented with crystalline Lys, Trp, and Thr (on an as-fed basis). Pigs gained at similar rates when fed the 16% CP diet or the 12% CP diet supplemented with Lys, Trp, and Thr (P > 0.10). Pigs fed the 12% CP, AA-supplemented diet had a gain:feed similar to pigs fed the 16% CP diet when housed in the 23 degrees C environment but had a lower gain:feed in the 33 degrees C environment (diet x temperature, P < 0.01). In Exp. 2, 702 gilts were allotted to six treatments with nine replicates per treatment. Average initial and final BW were 25.3 and 109.7 kg, respectively. Gilts were fed two levels of CP (high CP with minimal crystalline AA supplementation or low CP with supplementation of Lys, Trp, Thr, and Met) and three levels of NE (high, medium, or low) in a 2 x 3 factorial arrangement. A four-phase feeding program was used, with diets containing apparent digestible Lys levels of 0.96, 0.75, 0.60, and 0.48% switched at a pig BW of 41.0, 58.8, and 82.3 kg, respectively. Pigs fed the low-CP, AA-supplemented diets had rates of growth and feed intake similar to pigs fed the high-CP diets. Dietary NE interacted with CP level for gain:feed (P < 0.06). A decrease in dietary NE from the highest NE level decreased gain:feed in pigs fed the high-CP diet; however, gain:feed declined in pigs fed the low-CP, AA-supplemented diet only when dietary NE was decreased to the lowest level. There was a slight reduction in longissimus area in pigs fed the low-CP diets (P < 0.08), but other estimates of carcass muscle did not differ (P > 0.10). These data suggest that pigs fed low-CP, AA-supplemented diets have performance and carcass characteristics similar to pigs fed higher levels of CP and that alterations in dietary NE do not have a discernible effect on pig performance or carcass composition.

Two hundred sixteen crossbred barrows and gilts (84.3 kg BW) were used to test the effects of dietary energy density and lysine:energy ratio (Lys:ME) on the performance, carcass characteristics, and pork quality of finishing pigs fed 10 ppm ractopamine. Pigs were blocked by BW and gender, allotted to 36 pens (six pigs per pen), and pens were assigned randomly within blocks to dietary treatments (as-fed basis) arranged in a 2 x 3 factorial design, with two levels of energy (3.30 or 3.48 Mcal/kg) and three Lys:ME (1.7, 2.4, or 3.1 g lysine/Mcal) levels. Pigs were fed experimental diets for 28 d, and weights and feed disappearance were recorded weekly to calculate ADG, ADFI, and G:F. Upon completion of the feeding trial, pigs were slaughtered and carcass data were collected before fabrication. During carcass fabrication, hams were analyzed for lean composition using a ham electrical conductivity (TOBEC) unit, and loins were collected, vacuum-packaged, and boxed for pork quality data collection. Energy density had no (P> 0.22) effect on ADG or ADFI across the entire 28-d feeding trial; however, pigs fed 3.48 Mcal of ME were more (P < 0.02) efficient than pigs fed 3.30 Mcal of ME. In addition, ADG and G:F increased linearly (P < 0.01) as Lys:ME increased from 1.7 to 3.1 g/Mcal. Carcasses of pigs fed 3.48 Mcal of ME were fatter at the last lumbar vertebrae (P < 0.08) and 10th rib (P < 0.04), resulting in a lower (P < 0.03) predicted fat-free lean yield (FFLY). Conversely, 10th-rib fat thickness decreased linearly (P = 0.02), and LM depth (P < 0.01) and area (P < 0.01) increased linearly, with increasing Lys:ME. Moreover, FFLY (P < 0.01) and actual ham lean yield (P < 0.01) increased as Lys:ME increased in the diet. Dietary energy density had no (P > 0.19) effect on pork quality, and Lys:ME did not (P > 0.20) affect muscle pH, drip loss, color, and firmness scores. Marbling scores, as well as LM lipid content, decreased linearly (P < 0.01) as Lys:ME increased from 1.7 to 3.1 g/Mcal. There was a linear (P < 0.01) increase in shear force of cooked LM chops as Lys:ME increased in the finishing diet. Results indicate that 3.30 Mcal of ME/kg (as-fed basis) is sufficient for optimal performance and carcass leanness in pigs fed ractopamine. The Lys:ME for optimal performance and carcass composition seems higher than that currently used in the swine industry; however, feeding very high Lys:ME (> 3.0 g/Mcal, as-fed basis) to ractopamine-fed pigs may result in decreased marbling and cooked pork tenderness.

One hundred eight high-lean-growth gilts (34.4 kg BW) were used to determine the dietary lysine requirement to maximize growth, carcass characteristics, and protein accretion from 34 to 72.5 kg BW. The experiment was a randomized complete block design; initial BW served as the blocking factor. Six dietary treatments were included, ranging from .54 to 1.04% (.10% increments) digestible lysine (.69 to 1.25% total lysine). Pigs were housed in pens of three, with six replicate pens per treatment. Pig weights and feed consumption were collected weekly to calculate ADG, ADFI, and gain:feed (G/F). Initially, five pigs were slaughtered to determine baseline carcass composition. When the mean weight for pigs in a pen reached 55 and 72.5 kg, one pig per pen was randomly selected and slaughtered for carcass measurements. The right side of each carcass was ground twice and sampled to determine carcass composition and tissue accretion rates. Average daily gain was increased by dietary lysine from 34 to 55 kg (linear, P < .01), from 55 to 72.5 kg (linear, P < .10), and from 34 to 72.5 kg (linear, P < .01). Although ADFI from 34 to 55 and from 55 to 72.5 kg was not influenced by dietary lysine, ADFI for the entire experiment tended to decrease (quadratic, P < .10) as digestible lysine increased. Increased dietary lysine resulted in improved G/F from 34 to 55 kg (linear, P < .01) and from 55 to 72.5 and 34 to 72.5 kg (quadratic, P < .01). Average backfat thickness was not influenced by dietary lysine at 55 kg but decreased (linear, P < .05) as dietary lysine increased at 72.5 kg. At 55 kg, longissimus muscle area was larger (linear, P < .05) for gilts fed increased digestible lysine. However, longissimus muscle area was similar for all treatments at 72.5 kg. Gilts fed increased digestible lysine had greater CP accretion from 34 to 55 kg (linear, P < .01), 55 to 72.5 kg (linear, P < .05; quadratic, P < .10), and from 34 to 72.5 kg (quadratic, P < .05). Based on the feed intake observed in this study, the high-lean-growth gilt requires at least 22 g/d total lysine intake from 34 to 72.5 kg to maximize CP accretion.

One hundred twenty pigs (initially 44 kg BW) were used to determine effects of the interrelationship between genotype, sex, and dietary lysine on growth performance and carcass composition in a 2 x 2 x 2 factorial arrangement. Genetic comparisons were made between pigs characterized with either a high or medium potential for lean tissue gain. Within genotype, barrows and gilts were separately fed either a .90 or .70% lysine diet until the mean weight of pigs in each pen of three reached 104 kg. One pig per pen was slaughtered to determine carcass characteristics and chemical composition. From 104 to 127 kg, dietary lysine was lowered to .75 or .55% for pigs fed .90 or .70% dietary lysine, respectively. When the pigs' mean weight met or exceeded 127 kg, both pigs were slaughtered to determine carcass characteristics and chemical composition. Carcass length, longissimus muscle area, average backfat thickness, and 10th rib fat depth were measured 24 h postmortem on the chilled carcasses. The right side of each carcass was then ground and chemically analyzed to determine protein and lipid accretion rates. No interactions were detected from 44 to 104 kg; therefore, main effect means will be discussed. At 104 kg, high-lean pigs had increased ADG (P < .01) and gain:feed ratio (G/F; P < .05) compared with medium-lean pigs. Barrows had increased (P < .05) ADG and ADFI but exhibited a poorer (P < .01) G/F than gilts. Pigs fed .90% lysine had improved (P < .01) ADG compared with pigs fed .70% lysine.(ABSTRACT TRUNCATED AT 250 WORDS)

Three experiments were conducted to determine the effect of reducing NE, by adding dietary fiber in Exp. 1 and 2 and decreasing dietary fat in Exp. 3, of low-CP, crystalline amino acid (CAA)-supplemented diets for finishing pigs on growth performance and carcass characteristics. In Exp. 1 and 2, 64 barrows (Exp. 1) or gilts (Exp. 2) were allotted to four treatments with four replicates of four pigs each. Average initial and final BW were 74 and 117 kg in Exp. 1 and 74 and 102 kg in Exp. 2. The following diets were fed in Exp. 1: 1) corn-soybean meal (C-SBM); 2) low-CP (-3.5%), supplemented with CAA; 3) CAA + rice hulls (CAA+RH; NE equal to Diet 1); and 4) CAA+RH+OIL (NE equal to Diet 2). Experiment 2 was similar to Exp. 1, except RH were replaced with wheat middlings (WM), oil was replaced with dry fat, and the CP was decreased by 3.1% in the low-CP diets. In both experiments, serum urea-N (SUN, corrected for initial SUN by covariance analysis) was higher (P<.10) for pigs fed C-SBM than for pigs fed any other diet. In Exp. 1, barrows fed CAA+RH had lower hot carcass weight, percentage muscle, fat-free lean (FFLEAN), lean gain per day, retained energy (RE) in FFLEAN, and lean:fat ratio than barrows fed C-SBM, along with less FFLEAN than barrows fed CAA+RH+OIL. Barrows fed CAA+RH had smaller longissimus muscle areas than barrows fed any other diet, and barrows fed C-SBM had higher dressing percentage and lower percentage total fat than barrows fed any other diet. Barrows fed C-SBM had higher lean:fat ratio and lower total fat than barrows fed CAA. In Exp. 2, gilts fed CAA+WM+FAT had heavier heart weights than gilts fed C-SBM or CAA (P<.10). In Exp. 3, 702 gilts were allotted to six treatments with nine replicates of 13 gilts each. Average initial and final BW were 70 and 110 kg. Gilts were fed two levels of CP (15.5 or 11.7% plus CAA added to meet an ideal amino acid ratio) and three levels of NE (2,650, 2,617, or 2,584 kcal/kg), resulting in a 2x3 factorial arrangement of treatments. Gilts fed 15.5% CP had higher gain:feed ratio than gilts fed 11.7% CP (P<.01). Longissimus depth was greater for gilts fed 15.5% CP than for gilts fed 11.7% CP and was decreased as NE decreased only in gilts fed 11.7% CP (CP effect, P<.09; NE linear effect, P<.04; CP x NE effect, P<.01). Gilts fed the diet with 2,617 kcal NE had lighter carcasses and less total fat, fat gain per day, RE, and RE as fat regardless of protein level than gilts fed 2,650 or 2,584 kcal NE/kg (NE quadratic, P<.09). Loin color score increased as NE decreased (linear, P<.06), but longissimus fat depth was increased by the lowest level of NE (NE quadratic effect, P<.09). Overall, the reduction of NE in low-CP, CAA-supplemented diets did not affect growth performance and was not an effective means of reducing fat in finishing pigs.

A total of 1,956 weanling pigs were used in five experiments to evaluate spray-dried blood meal (SDBM) in starter pig diets. In Exp. 1, 432 weanling pigs (initially 6.9 kg BW and 21 d of age) were used to evaluate different protein sources in the d 7 to 28 postweaning diet. Pigs were fed a control diet containing 5% select menhaden fish meal or diets with 3.88% spray-dried porcine plasma, 2.49% SDBM (porcine), 5.74% soy protein concentrate, 5.74% moist extruded soy protein concentrate, or L-lysine.HCl and DL-methionine replacing select menhaden fish meal on an ideal protein basis. Pigs fed diets containing the spray-dried blood products had higher (P < .06) mean ADG than pigs fed the other protein sources. In Exp. 2, 744 weanling pigs (initially 5.8 kg BW and 21 d of age) were used to determine the effects of 0, 1, 2, 3, 4, or 5% SDBM (bovine) in the d 7 to 28 postweaning diet. Pigs fed increasing SDBM had greater (quadratic, P < .01) ADG and improved gain:feed ratio (G/F). Inflection point analysis projected optimum ADG and G/F at 1.9% SDBM. In Exp. 3, 216 weanling pigs (initially 10.9 kg BW and 42 d of age) were used to determine the effects of 0, .5, 1, 1.5, 2, and 2.5% SDBM (bovine) in the d 21 to 42 postweaning diet. Pigs fed increasing SDBM had decreased (linear, P < .05) ADG and G/F. In Exp. 4 and 5, 144 and 180 weanling pigs (initially 5.3 and 6.2 kg BW and 24 and 21 d of age, respectively) were used to evaluate either 2.5% spray-dried porcine, spray-dried bovine, or flash-dried bovine blood meal (Exp. 4) or 2.5% spray-dried bovine or spray-dried avian blood meal (Exp. 5). Pigs fed diets containing the spray-dried blood meals had improved ADG and G/F (P < .01) compared with pigs fed flash-dried blood meal. However, no differences (P > .10) were observed among treatments when pigs were fed spray-dried blood meals from different species. We conclude that spray-dried bovine, porcine, and avian blood meal are effective protein sources in starter pig diets (d 7 to 28 postweaning). However, SDBM is not necessary in the diets of older pigs (d 21 to 42 postweaning) for maximum growth performance.

One hundred fourteen high-lean growth gilts (72.5 kg BW) were used to determine the apparent digestible lysine requirement for maximum growth performance and carcass protein deposition rate from 72.5 to 136 kg BW. The experiment was a randomized complete block design with initial BW used to establish blocks. Six dietary treatments were included, ranging from .44 to .94% (.10% increments) apparent digestible lysine (.62 to 1.13% total lysine) with six replicate pens per treatment and three pigs per pen. Pig weights and feed consumption were collected weekly to determine ADG, ADFI, and gain: feed ratio (G/F). Six gilts were slaughtered at 72.5 kg BW to determine initial carcass composition. When the mean weight of pigs in a pen reached 104 or 136 kg, one pig per pen was selected (closest to 104 or 136 kg, respectively) and slaughtered for determination of carcass measurements and composition. From 72.5 to 104 kg and from 104 to 136 kg, ADG and G/F increased (linear, P < .05; quadratic, P < .10, respectively) as apparent digestible lysine increased. From 72.5 to 136 kg, G/F increased (quadratic, P < .10) as apparent digestible lysine increased. Average backfat thickness and longissimus muscle area at 104 kg were not influenced (P > .10) by apparent digestible lysine. However, average backfat thickness increased (quadratic, P < .05) with increasing digestible lysine for gilts slaughtered at 136 kg. Carcass CP accretion was not influenced (P > .10) from 72.5 to 104 kg but tended to increase (linear, P < .10) from 72.5 to 136 kg as digestible lysine increased. Plasma and longissimus muscle cholesterol concentrations were unaffected (P > .10) by increasing digestible lysine. These results suggest that high-lean growth gilts require greater dietary lysine than current NRC (1988) estimates to maximize ADG, G/F, and carcass CP accretion from 72.5 to 104 and from 104 to 136 kg.

Two experiments were conducted to determine the effect of dietary L-carnitine on growth performance and carcass composition of nursery and growing-finishing pigs. In Exp. 1,216 weanling pigs (initially 4.9 kg and 19 to 23 d of age) were used in a 35-d growth trial. Pigs were blocked by weight in a randomized complete block design (six pigs per pen and six pens per treatment). Four barrows and four gilts were used to determine initial carcass composition. L-Carnitine replaced ground corn in the control diets to provide 250, 500, 750, 1,000, or 1,250 ppm. On d 35, three barrows and three gilts per treatment (one pig/block) were killed to provide carcass compositions. L-Carnitine had no effect (P > 0.10) on growth, percentages of carcass CP and lipid, or daily protein accretion. However, daily lipid accretion tended to decrease and then return to values similar to those for control pigs (quadratic P < 0.10) with increasing dietary L-carnitine. In Exp. 2, 96 crossbred pigs (initially 34.0 kg BW) were used to investigate the effect of increasing dietary L-carnitine in growing-finishing pigs. Pigs (48 barrows and 48 gilts) were blocked by weight and sex in a randomized complete block design (two pigs/pen and eight pens/treatment). Dietary L-carnitine replaced cornstarch in the control diet to provide 25, 50, 75, 100, and 125 ppm in grower (34 to 56.7 kg; 1.0% lysine) and finisher (56.7 to 103 kg; 0.80% lysine) diets. At 103 kg, one pig/pen was slaughtered, and standard carcass measurements were obtained. Dietary L-carnitine did not influence growth performance (P > 0.10). However, increasing dietary carnitine decreased average and tenth-rib back-fat (quadratic, P < 0.10 and 0.05), and increased percentage lean and daily CP accretion rate (quadratic, P < 0.05). Break point analysis projected the optimal dosage to be between 49 and 64 ppm of L-carnitine for these carcass traits. It is concluded that dietary carnitine fed during the nursery or growing-finishing phase had no effect on growth performance; however, feeding 49 to 64 ppm of L-carnitine during the growing-finishing phase increased CP accretion and decreased tenth-rib backfat.