Utilization of crystalline or protein-bound lysine for growth and carcass traits of barrows and gilts fed individually or in groups

An experiment consisting of two 4-wk trials was conducted to determine Lys use for growth and carcass traits in barrows and gilts fed individually or in groups. One hundred twelve growing pigs (56 barrows and 56 gilts; average initial BW of 18.6 kg) were used in each trial. Pigs were fed individually or in groups of 3. There were 28 pigs individually penned, and 84 pigs in 28 pens (3 pigs/pen). There were 2 replications per treatment in each trial for a total of 4 replications. Dietary treatments consisted of a corn-soybean meal (SBM) basal diet (0.48% Lys) and diets containing 0.56%, 0.65%, and 0.74% standardized ileal digestible (SID) Lys that were achieved by adding Lys to the basal diet from either SBM or crystalline source as L-Lys HCL (CLys). At the end of each trial, all pigs were scanned using real-time ultrasound to determine 10th-rib back fat depth and LM area, and fat-free lean gain (FFLG) was calculated. Blood samples were taken from all pigs weekly to determine plasma urea N (PUN). Pigs fed CLys and Lys from SBM were not different in final BW, ADG, ADFI, or G:F. The ADG and G:F increased linearly (P < 0.01) as dietary Lys concentration increased. The SID Lys intake increased linearly (P < 0.01) as dietary Lys concentration increased and was not different when comparing pigs fed diets with CLys or SBM. The amount of SID Lys required per unit of growth or BW gain increased linearly (about 13 to 15.50 g/kg) in pigs fed either CLys or SBM Lys. Pigs fed individually had a greater (P < 0.05) ADG (0.59 vs. 0.57 kg) and ADFI (1.36 vs. 1.29 kg) than pigs fed in groups. The SID Lys intake was greater (P < 0.05) in pigs fed individually in comparison with pigs fed in a group (8.51 vs. 8.06 g/d). Fat-free lean gain and LM area increased (P < 0.01) as dietary Lys concentration increased regardless of Lys source. Pigs fed CLys diets had a greater (P < 0.05) LM area than pigs fed SBM at 0.74% SID Lys. Gilts had a greater (P < 0.01) LM area (14.28 vs. 13.58 cm(2)) and FFLG (264 vs. 245 g/d) than barrows. Pigs fed individually with CLys had less (P < 0.01) PUN than pigs fed Lys from SBM. Barrows fed individually had less (sex × feeding method, P < 0.01) PUN than gilts (26.75 vs. 29.32 g/100 mL). The results indicate that Lys from SBM-bound and CLys source were utilized similarly for growth and carcass traits regardless of sex or feeding method.

Genome-wide prediction of age at puberty and reproductive longevity in sows

Traditional selection for sow reproductive longevity is ineffective due to low heritability and late expression of the trait. Incorporation of DNA markers into selection programs is potentially a more practical approach for improving sow lifetime productivity. Using a resource population of crossbred gilts, we explored pleiotropic sources of variation that influence age at puberty and reproductive longevity. Of the traits recorded before breeding, only age at puberty significantly affected the probability that females would produce a first parity litter. The genetic variance explained by 1-Mb windows of the sow genome, compared across traits, uncovered regions that influence both age at puberty and lifetime number of parities. Allelic variants of SNPs located on SSC5 (27-28 Mb), SSC8 (36-37 Mb) and SSC12 (1.2-2 Mb) exhibited additive effects and were associated with both early expression of puberty and a greater than average number of lifetime parities. Combined analysis of these SNPs showed that an increase in the number of favorable alleles had positive impact on reproductive longevity, increasing number of parities by up to 1.36. The region located on SSC5 harbors non-synonymous alleles in the arginine vasopressin receptor 1A (AVPR1A) gene, a G-protein-coupled receptor associated with social and reproductive behaviors in voles and humans and a candidate for the observed effects. This region is characterized by high levels of linkage disequilibrium in different lines and could be exploited in marker-assisted selection programs across populations to increase sow reproductive longevity.

Effect of dietary acids on growth performance of nursery pigs: a cooperative study

An experiment involving 854 crossbred pigs (20 replicate pens of 4 to 8 pigs per pen) was conducted at 8 experiment stations to determine the effects of acids in nursery pig diets and their inclusion amounts on growth performance using diets and weaning ages typical of those used in the United States commercial pork industry. Diets were formulated to have constant a ME and contain 1.45, 1.45, and 1.30% standardized ileal digestible Lys for phases 1, 2, and 3, respectively. The basal diets were supplemented with various types and concentrations of acid at the expense of corn (Zea mays). Treatment diets included 0% acid (control), 0.1 or 0.2% phosphoric acid, 1 or 2% organic acids, and 0.1% phosphoric acid plus 1% organic acids with or without an antibiotic. The organic acids consisted of 50% citric acid and 50% fumaric acid by weight. All but the final diet contained the antibiotic carbadox. All diets contained 3,000 mg of Zn/kg diet from zinc oxide during phases 1 and 2 and had limited acid buffering capacity, ranging from 142, 127, and 122 mEq/kg of feed for phases 1, 2, and 3, respectively. At each participating station, pigs were randomly allotted to dietary treatments on the basis of their initial BW. Sex and ancestry were equally distributed across the treatments. Results indicated that treatment effects on pig performance were observed in phases 1 and 2 but not in phase 3. In phase 1, ADG of pigs fed 0.2% phosphoric acid was greater than that of pigs fed the combination of acids with no antibiotic (P = 0.041). In phase 2, pigs fed treatments containing an antibiotic had a greater ADG than those fed the combination of acids without antibiotic (P < 0.05). Addition of acids to diets did not affect growth performance during any phase or the overall period. Over the 4-wk study, growth rate was slowest on the treatment without antibiotic, with specific differences that were often statistically significant (P < 0.05). In summary, under the conditions of this experiment, the acid treatments had no effect but the antibiotic improved growth performance.

Corn distillers dried grains with solubles in diets for growing-finishing pigs: a cooperative study

An experiment involving 560 crossbred pigs (28 replications of 4 to 6 pigs per pen) was conducted at 9 research stations to assess the effects of dietary concentrations of corn distillers dried grains with solubles (DDGS) on pig performance and belly firmness. Fortified corn-soybean meal diets containing 0, 15, 30, or 45% DDGS were fed in 3 phases from 33 to 121 kg of BW. A common source of DDGS containing 90.1% DM, 26.3% CP, 0.96% Lys, 0.18% Trp, 9.4% crude fat, 34.6% NDF, 0.03% Ca, and 0.86% P was used at each station. Diets were formulated to contain 0.83, 0.70, and 0.58% standardized ileal digestible (SID) Lys during the 3 phases with diets changed at 60 and 91 kg of BW, respectively. The DDGS replaced corn and soybean meal, and up to 0.172% Lys and 0.041% Trp were added to maintain constant SID concentrations of Lys and Trp in each phase. At each station, 2 pigs from each pen in 2 replications were killed and a midline backfat core was obtained for fatty acid analysis and iodine value. In most instances, there were differences among stations (P < 0.01), but the station × treatment interactions were few. Body weight gain was linearly reduced in pigs fed the greater amounts of DDGS (0 to 45%) during phase I (950, 964, 921, and 920 g/d; P < 0.01) and over the entire experimental period (944, 953, 924, and 915 g/d; P = 0.03), but ADFI (2.73, 2.76, 2.68, and 2.70 kg) and G:F (347, 347, 345, and 341 g/kg) were not affected (P = 0.15 and P = 0.33, respectively) during the entire test. Backfat depth was reduced (linear, P < 0.02) by increasing amounts of DDGS (22.5, 22.7, 21.4, and 21.6 mm), but LM area (47.4, 47.4, 46.1, and 45.4 cm(2)) was not affected (P = 0.16) by treatments. Estimated carcass fat-free lean was 51.9, 52.2, 52.4, and 52.1% for 0 to 45% DDGS, respectively (linear, P = 0.06). Flex measures obtained at 6 stations indicated less firm bellies as dietary DDGS increased (lateral flex: 11.9, 8.6, 8.4, and 6.6 cm; linear, P < 0.001; vertical flex: 26.1, 27.4, 28.2, and 28.7 cm; linear, P < 0.003). Saturated and monounsaturated fatty acid concentrations in subcutaneous fat decreased linearly (P < 0.001) and PUFA concentrations increased linearly (P < 0.001) with increasing DDGS in the diet. Iodine values in inner (61.1, 68.2, 74.7, and 82.2) and outer (67.9, 73.6, 79.6, and 85.8) backfat increased linearly (P < 0.001) as DDGS in the diet increased. In this study, feeding diets with 30 or 45% DDGS did not have major effects on growth performance, but resulted in softer bellies. Regression analysis indicated that iodine values increased 4.3 units for every 10 percentage unit inclusion of DDGS in the diet.

Targeting of an interrupted polypurine:polypyrimidine sequence in mammalian cells by a triplex-forming oligonucleotide containing a novel base analogue

The DNA triple helix consists of a third strand of nucleic acid lying in the major groove of an intact DNA duplex. The most stable triplexes form on polypurine:polypyrimidine sequences, and pyrimidine interruptions in the purine strand are destabilizing. Sequence stringency is imparted by specific Hoogsteen hydrogen bonds between third strand bases and the purine bases in the duplex. Appropriate base and sugar modifications of triple helix-forming oligonucleotides (TFOs) confer chromosome targeting activity in living cells. However, broad utilization of TFOs as gene targeting reagents in mammalian cells has been limited by the requirement for homopurine target sequences. Although there have been a number of base analogues described that appear to be promising as candidates for triplex target expansion, none has been examined in a biological system. We have employed a postsynthetic strategy to prepare a collection of TFOs with base analogues at a defined position. Following assessment of affinity for a triplex target with a single C:G inversion, TFOs with a second generation of analogues were synthesized. One of these, TFO-5a, with 2'-OMe-guanidinylethyl-5-methylcytosine at the position corresponding to the C:G interruption in the target sequence, was further modified to confer bioactivity. The activity of this TFO, linked to psoralen, was measured in a mammalian cell line that was engineered by directed sequence conversion to carry a triplex target with a single C:G interruption. TFO-5a was active against this target and inactive against the corresponding target with an uninterrupted polypurine:polypyrimidine sequence.

Extremophile-inspired strategies for enzymatic biomass saccharification

Domestic ethanol production in the USA relies on starch feedstocks using a first generation bioprocess. Enzymes that contribute to this industry remain of critical value in new and established markets as commodity additives and for in planta production. A transition to non-food feedstocks is both desirable and essential to enable larger scale production. This objective would relieve dependence on foreign oil and strengthen the national economy. Feedstocks derived from corn stover, wheat straw, perennial grasses and timber require pretreatment to increase the accessibility of the cellulosic and hemicellulosic substrates to commodity enzymes for saccharification, which is followed by fermentation-based conversion of monosaccharides to ethanol. Hot acid pretreatment is the industrial standard method used to achieve deconstruction of lignocellulosic biomass. Therefore, enzymes that tolerate both acid and heat may contribute toward the improvement of lignocellulosic biomass processing. These enzymes are produced naturally by extremely thermophilic microbes, sometimes called extremophiles. This review summarizes information on enzymes from selected (acido)thermophiles that mediate saccharification of alpha- and beta-linked carbohydrates of relevance to biomass processing.

Effect of phytase on apparent total tract digestibility of phosphorus in corn-soybean meal diets fed to finishing pigs

Five experiments were conducted to investigate the ability of different phytase products to improve P digestibility in finishing pigs. A corn-soybean meal basal diet containing 0.50% Ca, 0.32% P, and 0.40% Cr(2)O(3) was used to calculate apparent P and GE digestibility. Pigs were individually penned and fed their respective diet for ad libitum intake for 12 d before fecal sampling on d 13 and 14 and blood collection on d 14 for plasma P determination. Experiments 1 through 4 used gilts with across-trial average initial and final BW of 84 and 97 kg, respectively. Pigs were fed Natuphos (Exp. 1), OptiPhos (Exp. 2), Phyzyme (Exp. 3), or RonozymeP (Exp. 4) at 0, 200, 400, 600, 800, or 1,000 phytase units (FTU)/kg (where 1 FTU is defined as the quantity of enzyme required to liberate 1 micromol of inorganic P per min, at pH 5.5, from an excess of 15 micromol/L of sodium phytate at 37 degrees C). Experiment 5 used barrows with initial and final BW of 98 and 111 kg, respectively, and were fed diets containing 0, 500, or 1,000 FTU/kg of Natuphos, OptiPhos, Phyzyme, or RonozymeP. Pigs fed Natuphos (Exp. 1) and OptiPhos (Exp. 2) exhibited a linear and quadratic (P < 0.01) improvement in P digestibility with increasing levels of dietary phytase, whereas pigs fed Phyzyme (Exp. 3) and RonozymeP (Exp. 4) exhibited a linear (P < 0.01) improvement in apparent P digestibility with increasing levels of dietary phytase. In Exp. 5, the improvement in apparent P digestibility with increasing levels of dietary phytase was linear (P < 0.01) for Natuphos, Phyzyme, and RonozymeP, but was linear and quadratic (P < 0.01) for OptiPhos. Based on regression analysis, inorganic P release at 500 FTU/kg was predicted to be 0.070, 0.099, 0.038, and 0.030% for Natuphos, OptiPhos, Phyzyme, and RonozymeP, respectively. These estimates are comparable with those of pigs in Exp. 5, for which the estimated inorganic P release at 500 FTU/kg was 0.102, 0.039, and 0.028% for OptiPhos, Phyzyme, and RonozymeP, respectively, but not for the 0.034% value determined for Natuphos. The effect of dietary phytase on GE digestibility was inconsistent with a linear (P < 0.01) improvement in GE digestibility noted for OptiPhos (Exp. 2 and 5) and RonozymeP (Exp. 4), but the quadratic (P < 0.01) improvement for Natuphos. There was no effect of dietary phytase on plasma inorganic P. The data presented show clear improvements in P digestibility, with the estimated level of inorganic P release being dependent on phytase source and level.

Performance of growing-finishing pigs fed diets containing YieldGard Rootworm corn (MON 863), a nontransgenic genetically similar corn, or conventional corn hybrids

Two studies were conducted at two locations to evaluate growth performance and carcass characteristics of growing-finishing pigs fed diets containing either YieldGard Rootworm corn (MON 863), a non-transgenic genetically similar corn (RX670), or two conventional nontransgenic corn hybrids (DK647 and RX740). A randomized complete block design with a 2 x 4 factorial arrangement of treatments (two genders and four corn hybrids) was used. Study 1 used 72 barrows and 72 gilts (progeny of Danbred sires x [Danbred x NE White line] dams grown from 22.7 to 117.0 kg BW). Pigs were housed in a modified open-front building in single-gender groups of six (six pens per dietary treatment). Study 2 used 80 barrows and 80 gilts (progeny of PIC 337 sires x C22 dams) grown from 29.5 to 114.9 kg BW. Pigs were housed in an environmentally controlled finishing building in single-gender groups of five (eight pens per dietary treatment). The test corns were included at a fixed proportion of the diet in both studies. Animals had ad libitum access to feed and water. Pigs were slaughtered at the end of the growth period using standard procedures, and carcass measurements were taken. There were no diet x gender interactions for growth performance or carcass measurements in either study. In both studies, overall ADG, ADFI, and G:F were not affected by corn hybrid. There was no effect of corn hybrid on carcass or LM quality measurements in Study 1. In Study 2, LM protein content was less (P< 0.05) for pigs fed RX740 compared with those fed either MON 863 or RX670; however, there was no effect of corn hybrid on other LM composition measures or on quality traits. In both studies, differences between barrows and gilts for growth and carcass traits were similar to previous research. These results suggest that the YieldGard Rootworm corn (MON 863) results in equivalent growth performance and carcass quality to nontransgenic corn hybrids in growing-finishing pigs.

Evaluating the effects of supplemental B vitamins in practical swine diets during the starter and grower-finisher periods—A regional study1,2

Two experiments were conducted to evaluate dietary fortification levels of a B vitamin pre-mix for starter and grower-finisher pigs on subsequent performance responses. The objective was to determine whether the modern pig requires higher dietary levels of B vitamins than estimated by the NRC (1998). Both experiments added fat-soluble vitamins at the requirement levels (NRC, 1998) in all diets, whereas the B vitamins were added at 0, 100, 200, or 400% of the total NRC (1998) requirement levels for the starter and grower pig. Indigenous vitamin contributions from the feed grains were not included in the estimates. Each station used the same vitamin premixes but incorporated its own grain sources in the diets. The first experiment was conducted across 7 stations (Indiana, Ohio, Oklahoma, Michigan, Missouri, Nebraska, Texas) and involved 660 pigs in a randomized complete block design in 30 replicates. Complex nursery diets were fed in 2 phases. The first phase (0 to 14 d postweaning) and second phase (15 to 35 d postweaning) diets were formulated to Lys (total) levels of 1.50 and 1.30%, respectively. The results demonstrated no performance response to addition of B vitamins from 0 to 14 d post-weaning, but performances increased quadratically (P < 0.01) to the 100% NRC level from 14 to 35 d postweaning and for the overall 35-d period. The second experiment was conducted across 3 stations (Ohio, Nebraska, and South Dakota) and involved 216 pigs in a randomized complete block design in 10 replicates. Corn-soybean meal mixtures were fed in 3 phases formulated to total Lys levels of 1.30% (23 to 55 kg of BW), 1.00% (55 to 85 kg of BW), and 0.78% (85 to 120 kg of BW). Pig performances increased (P < 0.01) to the 100% B vitamin level from 23 to 85 kg of BW, but there was no response to any level from 85 to 120 kg of BW. Carcass measurements demonstrated a greater LM area (P < 0.01) and a lower backfat depth (P < 0.01) to the 100% B vitamin level. One station evaluated an additional treatment (3 replicates) in which each replicate was fed a fifth diet containing the 100% dietary level of B vitamins from 23 to 85 kg of BW whereupon the B vitamins were removed from 85 to 120 kg of BW. This removal did not reduce pig performance responses for the final period or for the overall period. The results demonstrated that supplementation of B vitamins at the 100% total NRC levels for starter and grower pigs was sufficient to meet their needs, and there was no further improvement to or deleterious effect to greater dietary levels.

Tools and techniques for disease risk assessment in threatened wildlife conservation programmes

Disease plays a significant role as a risk factor in wildlife conservation programmes involving animal movements, such as translocation, transportation among zoos or reintroduction. However, the traditional 'zero-risk tolerance' approach to the assessment of disease risk in these programmes is unattainable and unmanageable, often leading to an excessively cautious attitude towards the risks that are involved. It is therefore critically important to develop a comprehensive, unified and broadly applicable set of descriptive and analytical tools that can more realistically and accurately assess disease-based risks in conservation-based animal-movement programmes. The Conservation Breeding Specialist Group, of the IUCN - World Conservation Union, has brought together an international team of wildlife medicine professionals to construct a set of qualitative and quantitative tools to assess disease risk. The tools are flexible, intuitive and span a broad range of complexities. These tools are designed to enable professionals to incorporate not only published, statistically valid data but also to make reasonable decisions under conditions of uncertainty, and to capture valuable information from more basic field or clinical experience. Selected tools from the larger 'toolkit' are described here, with examples from actual case studies where available.

Effects of replacing pharmacological levels of dietary zinc oxide with lower dietary levels of various organic zinc sources for weanling pigs1,2

Two 28-d randomized complete block design experiments were conducted to evaluate the effects of concentrations and sources of Zn on growth performance of nursery pigs. Seven stations participated in Exp. 1, which evaluated the efficacy of replacing 2,500 ppm of Zn from ZnO with 125, 250, or 500 ppm of Zn from Zn methionine. A control diet with 125 ppm of supplemental Zn was included at all stations. A total of 615 pigs were used in 26 replicates. Average weaning age was 20.6 d and the average initial BW was 6.3 kg. There were no differences in any growth response among the three supplemental Zn methionine levels fed in Exp. 1. Zinc supplementation from Zn methionine improved ADG compared with the control during all phases (P < 0.05), due primarily to an increase in ADFI. Pigs fed 2,500 ppm of Zn from ZnO gained faster (P < 0.01) than those fed the control diet during all phases, and faster (P < 0.05) than those fed supplemental Zn from Zn methionine for the 28-d experiment. Differences in gain were again due mainly to differences in feed intake. A second experiment compared five sources of supplemental organic Zn (500 ppm of Zn) with 500 and 2,000 ppm supplemental Zn from ZnO and a control (140 ppm total Zn). Six stations used a total of 624 pigs, with an average weaning age of 20.4 d and averaging 6.2 kg BW in 15 replicates. Pigs fed 2,000 ppm of Zn from ZnO gained faster (P < 0.05) than pigs fed the control or any of the 500 ppm of Zn treatments (ZnO or organic Zn). Pigs fed the 2,000 ppm of Zn from ZnO also consumed more feed than those receiving 500 ppm of Zn from ZnO or from any of the organic Zn sources (P < 0.05). Organic sources of Zn did not improve gain, feed intake, or feed efficiency beyond that achieved with the control diet. Supplemental Zn at a concentration of 500 ppm, whether in the form of the oxide or in an organic form, was not as efficacious for improved ADG as 2,000 to 2,500 ppm of Zn from ZnO.

Response of barrows to space allocation and ractopamine1,2,3

An experiment using 264 crossbred barrows was conducted to examine the interaction between space allocation and dietary ractopamine addition on pig performance and carcass characteristics using a 2 x 2 factorial arrangement of treatments. Treatments were 0.55 (19 pigs per pen) or 0.74 (14 pigs per pen) m2/pig from start (29.7 +/- 0.1 kg BW) to slaughter (108 kg BW) in a fully slatted facility and 0 or 10 ppm (as-fed basis) ractopamine for 28 d before slaughter. There were few treatment interactions. Pigs given 0.55 m2/pig had a lower ADG (P = 0.010), ADFI (P = 0.088), 10th-rib backfat depth on d 86 (P = 0.010), and carcass loin muscle depth (P = 0.011) than pigs given 0.74 m2/pig. There was no difference in feed conversion (P = 0.210) as a result of space allocation. Pigs fed diets containing 10 ppm ractopamine had decreased (P = 0.004) ADFI and improved (P = 0.001) feed conversion efficiencies for the 28-d feeding period, along with greater loin depth (P = 0.005) and carcass lean percent (P = 0.001). The improvements in 28-d carcass lean growth associated with feeding 10 ppm ractopamine resulted in an improvement in overall daily fat-free lean gain (P = 0.046). Under these experimental conditions, the response to dietary ractopamine was similar for crowded and uncrowded pigs.

Effect of feather meal on barrow performance1

One hundred ninety-six crossbred barrows of high lean gain potential (21.2 kg BW) were used in an experiment to determine the effect of dietary feather meal (FM) on barrow performance, specifically, the effects of the ingredient on ADG and carcass leanness. Additionally, 28 gilts (26.8 kg BW) were used to compare gender differences on the corn-soybean meal control diets. Treatments were control barrows and control gilts fed corn-soybean meal diets, and barrows fed according to a 2 x 3 factorial arrangement of FM levels (10 or 20%, as-fed basis) and starting weights on the diets (36, 60, or 86 kg BW). All barrow diets were formulated to contain the same apparent digestible lysine and ME. Control barrows ate more feed (2.61 vs. 2.39 kg/d; as-fed), grew faster (0.911 vs. 0.827 kg/d), had greater backfat depth at slaughter (15.6 vs. 11.6 mm), and had lower carcass lean content (P < 0.001), with no difference in daily lean gain (P = 0.848) compared with gilts. There was a linear (P = 0.010) decrease in ADG for barrows fed increasing amounts of FM from 36 kg BW to slaughter, with no effect of FM additions on ADG when initiated at 60 or 86 kg BW. There was a quadratic reduction (P = 0.008) in ADFI and estimated digestible lysine intake with increasing FM for the 36 to 60 kg BW period for barrows fed FM starting at 36 kg BW. There was a linear (P = 0.006) decrease in ADFI for the 60 to 86 kg BW period with increasing FM for barrows started on FM at 60 kg BW. There was no effect of experimental diets or starting weight on barrow 10th-rib backfat depth at slaughter. These results suggest that diets containing 10 and 20% FM were effective in decreasing overall ADG and ADFI by barrows when feeding of FM was initiated at 36 kg BW; however, backfat at slaughter was still greater than for control gilts.

Growth, carcass traits, and plasma amino acid concentrations of gilts fed low-protein diets supplemented with amino acids including histidine, isoleucine, and valine

Three experiments were conducted to determine the fifth-limiting amino acid for growing pigs in an 11% CP, corn-soybean meal diet. In each experiment, 36 gilts (initial weight 19.5, 21.9, and 21.0 kg, respectively) were penned individually and fed one of six diets in a randomized block design for 35 d. Diets containing 16, 12, and 11% CP were fed in each experiment. All 12 and 11% CP diets were supplemented with lysine, tryptophan, threonine, and methionine to provide the same total concentrations as those in the 16% CP diet. In Exp. 1, the 11% CP diet was supplemented with isoleucine, valine, or isoleucine + valine to concentrations equal to those in the 16% CP diet. In Exp. 2, the 11% CP diet was supplemented with histidine, histidine + valine, or histidine + isoleucine + valine. In Exp. 3, the 11% CP diet was supplemented with valine, histidine + valine, or isoleucine + valine. Gilts were allowed free access to feed and water. In all experiments, ADG and feed efficiency (G/F) were reduced (P < or = 0.07) as dietary protein was reduced. Supplementation of isoleucine alone further reduced (P < 0.05) ADG, ADFI, G/F, and fat-free lean gain. In contrast, supplementation of valine alone resulted in numerical increases in ADG and ADFI in two experiments, although the differences were not significant (P > 0.05). Supplementation with histidine and valine together resulted in growth performance equal to or greater than that of pigs fed the 12% CP diet, but less than that of pigs fed the 16% CP diet. Supplementation of isoleucine and valine together resulted in better growth performance (P < 0.05) than supplementation of either amino acid alone. In two experiments (Exp. 1 and 3), supplementation of the 11% CP diet with isoleucine and valine together resulted in ADG that were not significantly different (P > 0.05) from those of pigs fed the 16% CP diet. Supplementation of all three amino acids (Exp. 2) did not improve performance over supplementations with histidine and valine. Plasma urea concentrations were reduced (P < 0.05) as dietary protein was lowered from 16 to 12%. Additions of crystalline amino acids did not affect plasma urea levels. Plasma amino acid concentrations reflected the dietary additions of crystalline amino acids, but did not assist in the identification of the sequence of limiting amino acids. These data suggest that valine is the fifth-limiting amino acid and that either histidine or isoleucine is the sixth-limiting amino acid in an 11% CP diet.

Nitrogen metabolism and growth performance of gilts fed standard corn-soybean meal diets or low-crude protein, amino acid-supplemented diets

Two experiments were conducted to determine the CP concentration below which N retention and growth performance are reduced when low-protein, amino acid-supplemented, corn-soybean meal diets are fed. In a N balance trial (Exp. 1), 12 gilts (initial weight 41 kg) were fitted with urinary catheters and fed six different diets during three 7-d periods in an incomplete block design. The diets were: 1) 18% CP; 2) 14% CP + AA, 3) 16% CP; 4) 12% CP + AA; 5) 14% CP; and 6) 10% CP + AA. Amino acids (lysine, threonine, tryptophan, and methionine) were supplemented such that the concentrations in the low-protein diets were equal to those in their standard (4% CP higher) counterparts. Nitrogen retention (g/d) decreased (P < 0.01) as CP decreased, in both standard (27.10, 24.53, and 20.99) and low-protein (21.51, 19.18, and 15.83) diets, but was lower (P < 0.01) in low-protein diets. There were no differences among treatments (P > 0.05) in biological value (68.2% standard vs 71.0% low-protein). In a growth performance trial (Exp. 2), 36 gilts (initial weight 19.5 kg) were penned individually and fed one of six diets for 35 d in a randomized complete block design. Dietary treatments were a 16% CP standard diet and low-protein diets formulated to contain 15, 14, 13, 12, and 11% CP supplemented with crystalline lysine, tryptophan, threonine, and methionine to equal the total concentrations in the standard diet. Protein concentration affected (P < or = 0.05) ADG, ADFI, feed efficiency, fat-free lean gain, longissimus muscle area, plasma urea, and plasma concentrations of most essential AA. For most of these traits, the major difference was poor performance of pigs fed the 11% CP diet. Thus, in Exp. 1, at AA concentrations from deficient to excess, low-protein, amino acid-supplemented diets failed to produce the same N retention as the equivalent corn-soybean meal diets. However in Exp. 2, the same performance was obtained with 16, 15, 14, 13, and 12% CP. Based on these data, we suggest that N balance is more sensitive than growth to amino acid adequacy andthat other AA (e.g., isoleucine and valine) may limit growth performance when the protein concentration is reduced by more than four percentage units.