Effects of restricting energy during the gilt development period on growth and reproduction of lines differing in lean growth rate: Responses in reproductive performance and longevity

Longevity and reproductive performance are economically important traits in the swine industry that are largely influenced by nutrition and other environmental factors. Reproductive performance and longevity through 4 parities was assessed in gilts of 2 genetic lines developed on ad libitum access to feed or restricted to 75% of ad libitum intake. A total of 661 gilts were used in a 2 x 2 factorial with half of the gilts allocated to an ad libitum diet (AL; n = 330), while the other half were energy restricted by 25% (R; n = 331) from 123 to 235 d of age. All gilts were sired by an industry maternal line. Dams of the gilts were from either a Large White by Landrace industry maternal line or Nebraska Selection Line 45X, producing gilts designated as W x L (n = 355) and L45X (n = 306), respectively. Daily estrus detection began at 140 d of age to obtain age at puberty (AP). Gilts (n = 510) were mated on their second or later estrus, beginning at 240 d of age. Sow weight and backfat were recorded at 110 d of gestation and weaning of each parity. Number of live-born, stillborn, and mummified pigs per litter and piglet birth and weaning weights were recorded through 4 parities. More L45X than W x L and more AL than R gilts reached puberty by 230 d of age (P < 0.01). Dietary treatment did not affect probability to produce parities 1 to 4 or any litter trait analyzed. The L45X females tended to be more likely to produce parities 1 (P < 0.08) and 3 (P < 0.06), while W x L had heavier litters at birth (P < 0.01) and weaning (P = 0.01). Treatment by parity interactions (P < 0.01) existed for weight and backfat prior to farrowing and backfat at weaning, and weight at weaning exhibited a line by treatment by parity interaction (P = 0.04) as R sows had lower weights and backfats in earlier parities, but caught up to AL sows in later parities. A treatment by parity interaction (P < 0.01) was also present for backfat loss from farrowing to weaning as R gilts lost less backfat than AL in parities 1 and 2, but more in parities 3 and 4. No significant differences were detected between lines or treatments for lifetime production traits. The populations of pigs and data presented here provide a framework for a diverse array of further studies. Alternative approaches to restrict energy have been assessed in addition to methods of marker-assisted and genomic selection for improvement of litter size and sow longevity.

Factors that affect heat production in lactating Jersey cows

Heat production (HP) represents a major energy cost in lactating dairy cows. Better understanding of factors that affect HP will improve our understanding of energy metabolism. Our objective was to derive models to explain variation in HP of lactating Jersey cows. Individual animal-period data from 9 studies (n = 293) were used. The data set included cows with a wide range (min to max) in days in milk (44-410) and milk yield (7.8-43.0 kg/d). Diets included corn silage as the predominate forage source, but diets varied (min to max on DM basis) in crude protein (CP; 15.2-19.5%), neutral detergent fiber (NDF; 35.5-43.0%), starch (16.2-31.1%), and crude fat (2.2 to 6.4%) contents. Average HP was (mean ± standard deviation) 22.1 ± 2.86 Mcal/d, or 28.1 ± 3.70% of gross energy intake. Eight models were fit to explain variation in HP: (1) dry matter intake (DMI; INT); (2) milk fat, protein, and lactose yield (MILKCOMP); (3) INT and milk yield (INT+MY); (4) INT and MILKCOMP/DMI (INT+MILKCOMP); (5) mass of digested NDF, CP, and starch (DIG); (6) INT and digested energy (INT+DE); (7) INT and NDF, CP, and starch digestibility (INT+DIG); or (8) INT+MILKCOMP model plus urinary N excretion (INT+MILKCOMP+UN). For all HP models, metabolic body weight was included. All models were derived via a backward elimination approach and included the random effects of study, cow, and period within block within study. The INT models adequately explained variation in HP with a nonrandom effect-adjusted concordance correlation coefficient of 0.84. Similar adjusted concordance correlation coefficients (0.79-0.85) were observed for other HP models. The HP associated with milk protein yield and supply of digestible protein was greater than other milk production and nutrient digestibility variables. The HP associated with urinary N excretion was 5.32. Overall, HP can be adequately predicted from metabolic body weight and DMI. Milk component yield, nutrient digestibility, or urinary N excretion explained similar variation as DMI. Coefficients for milk protein and protein digestion suggest that digestion and metabolism of protein and synthesis of milk protein contribute substantially to HP of a dairy cow.

Development of feed composition tables using a statistical screening procedure

Millions of feed composition records generated annually by testing laboratories are valuable assets that can be used to benefit the animal nutrition community. However, it is challenging to manage, handle, and process feed composition data that originate from multiple sources, lack standardized feed names, and contain outliers. Efficient methods that consolidate and screen such data are needed to develop feed composition databases with accurate means and standard deviations (SD). Considering the interest of the animal science community in data management and the importance of feed composition tables for the animal industry, the objective was to develop a set of procedures to construct accurate feed composition tables from large data sets. A published statistical procedure, designed to screen feed composition data, was employed, modified, and programmed to operate using Python and SAS. The 2.76 million data received from 4 commercial feed testing laboratories were used to develop procedures and to construct tables summarizing feed composition. Briefly, feed names and nutrients across laboratories were standardized, and erroneous and duplicated records were removed. Histogram, univariate, and principal component analyses were used to identify and remove outliers having key nutrients outside of the mean ± 3.5 SD. Clustering procedures identified subgroups of feeds within a large data set. Aside from the clustering step that was programmed in Python to automatically execute in SAS, all steps were programmed and automatically conducted using Python followed by a manual evaluation of the resulting mean Pearson correlation matrices of clusters. The input data set contained 42, 94, 162, and 270 feeds from 4 laboratories and comprised 25 to 30 nutrients. The final database included 174 feeds and 1.48 million records. The developed procedures effectively classified by-products (e.g., distillers grains and solubles as low or high fat), forages (e.g., legume or grass-legume mixture by maturity), and oilseeds versus meal (e.g., soybeans as whole raw seeds vs. soybean meal expellers or solvent extracted) into distinct sub-populations. Results from these analyses suggest that the procedure can provide a robust tool to construct and update large feed data sets. This approach can also be used by commercial laboratories, feed manufacturers, animal producers, and other professionals to process feed composition data sets and update feed libraries.

Increasing the concentration of linolenic acid in diets fed to Jersey cows in late lactation does not affect methane production

Although the inclusion of fat has reduced methane production in ruminants, relatively little research has been conducted comparing the effects of source and profile of fatty acids on methane production in lactating dairy cows. A study using 8 multiparous (325 ± 17 DIM; mean ± SD) lactating Jersey cows was conducted to determine effects of feeding canola meal and lard versus extruded byproduct containing flaxseed as a high-C18:3 fat source on methane production and diet digestibility in late-lactation dairy cows. A crossover design with 32-d periods (28-d adaptation and 4-d collections) was used to compare 2 different fat sources. Diets contained approximately 50% forage mixture of corn silage, alfalfa hay, and brome hay; the concentrate mixture changed between diets to include either (1) a conventional diet of corn, soybean meal, and canola meal with lard (control) or (2) a conventional diet of corn and soybean meal with an extruded byproduct containing flaxseed (EXF) as the fat source. Diets were balanced to decrease corn, lard, and canola meal and replace them with soybean mean and EXF to increase the concentration of C18:3 (0.14 vs. 1.20% of DM). Methane production was measured using headbox-style indirect calorimeters. Cattle were restricted to 95% ad libitum feed intake during collections. Milk production (17.4 ± 1.04 kg/d) and dry matter intake (15.4 ± 0.71 kg/d) were similar among treatments. Milk fat (5.88 ± 0.25%) and protein (4.08 ± 0.14%) were not affected by treatment. For methane production, no difference was observed for total production (352.0 vs. 349.8 ± 16.43 L/d for control vs. EXF, respectively). Methane production per unit of dry matter intake was not affected and averaged 23.1 ± 0.57 L/kg. Similarly, methane production per unit of energy-corrected milk was not affected by fat source and averaged 15.5 ± 0.68 L/kg. Heat production was similar, averaging 21.1 ± 1.02 Mcal/d. Digestibility of organic matter, neutral detergent fiber, and crude protein was not affected by diet and averaged 69.9, 53.6, and 73.3%, respectively. Results indicated that increasing C18:3 may not affect methane production or digestibility of the diet in lactating dairy cows.

GENOMICS SYMPOSIUM: Using genomic approaches to uncover sources of variation in age at puberty and reproductive longevity in sows

Genetic variants associated with traits such as age at puberty and litter size could provide insight into the underlying genetic sources of variation impacting sow reproductive longevity and productivity. Genomewide characterization and gene expression profiling were used using gilts from the University of Nebraska-Lincoln swine resource population ( = 1,644) to identify genetic variants associated with age at puberty and litter size traits. From all reproductive traits studied, the largest fraction of phenotypic variation explained by the Porcine SNP60 BeadArray was for age at puberty (27.3%). In an evaluation data set, the predictive ability of all SNP from high-ranked 1-Mb windows (1 to 50%), based on genetic variance explained in training, was greater (12.3 to 36.8%) compared with the most informative SNP from these windows (6.5 to 23.7%). In the integrated data set ( = 1,644), the top 1% of the 1-Mb windows explained 6.7% of the genetic variation of age at puberty. One of the high-ranked windows detected (SSC2, 12-12.9 Mb) showed pleiotropic features, affecting both age at puberty and litter size traits. The RNA sequencing of the hypothalami arcuate nucleus uncovered 17 differentially expressed genes (adjusted < 0.05) between gilts that became pubertal early (<155 d of age) and late (>180 d of age). Twelve of the differentially expressed genes are upregulated in the late pubertal gilts. One of these genes is involved in energy homeostasis (), a function in which the arcuate nucleus plays an important contribution, linking nutrition with reproductive development. Energy restriction during the gilt development period delayed age at puberty by 7 d but increased the probability of a sow to produce up to 3 parities ( < 0.05). Identification of pleotropic functional polymorphisms may improve accuracy of genomic prediction while facilitating a reduction in sow replacement rates and addressing welfare concerns.

Evaluation of collection method and diet effects on apparent digestibility and energy values of swine diets

Two experiments were conducted to investigate the effects of collection method and diet type on digestibility coefficients. In Exp. 1, 24 barrows were fed either a corn-soybean meal (CSBM) diet or CSBM with 20% dried distillers' grains with solubles (CSBM-DDGS). In Exp. 2, the effects of basal diet and collection method on determination of dried distillers' grains with solubles (DDGS) digestibility were studied using 24 barrows. The 4 diets used in Exp. 2 were: a CSBM (basal 1) , a barley-canola meal (BCM; basal 2), 80% basal 1 with 20% DDGS (CSBM-DDGS), and 80% basal 2 with 20% DDGS (BCM-DDGS). In both experiments, feces were collected using a time-based collection method (DY) or a "marker-to-marker" collection method (MM). Diets contained 0.5% of titanium dioxide (TiO) for estimating digestibility using the index marker approach (IM). The apparent total tract digestibility (ATTD) of DM and GE were lower ( < 0.05) in the CSBM-DDGS diet than in the CSBM diet in Exp. 1 but were not different in Exp. 2. All the estimates of BCM-based diets were consistently lower ( < 0.05) than those of CSBM-based diets. In Exp. 1, digestibility coefficients determined by the DY and MM were not different from each other, whereas those estimates were lower ( < 0.05) using the IM than those using the total collection approach (TC; DY and MM). In Exp. 2, interactions ( < 0.05) were observed between diet type and method for dietary digestibility coefficients. Digestibility and energy values estimated by the DY and MM were not different in pigs fed CSBM-based diets and the BCM-DDGS diet, whereas those estimates were greater ( < 0.05) using the DY than those using the MM in pigs fed the BCM. There were no interactions between basal diet and method for estimating DDGS digestibility. The ATTD of DM and GE of DDGS using the MM were greater ( < 0.05) than those using the IM, and ATTD of N tended to be greater ( < 0.10) using the MM than that using the IM. All estimates using the DY were not different from those using the MM or the IM, except that DE of DDGS was greater ( < 0.05) using the DY than when using the IM. Digestibility estimates of DDGS were not affected by basal diets. The mean DE and ME (as-fed basis) of DDGS were 3,994 and 3,688 kcal/kg, respectively, when estimated using the basal 1 diet and were 3,919 and 3,547 kcal/kg, respectively, when estimated using the basal 2 diet. In conclusion, both collection methods can be used to estimate energy and nutrient digestibility of diets and DDGS when using CSBM-based diets.

Body composition, tissue deposition, and lysine utilization for protein deposition of barrows and gilts fed crystalline or protein-bound lysine

An experiment with 2 trials (28 d/trial) was conducted to determine body composition, tissue deposition, and utilization of Lys for protein deposition (PD) of barrows and gilts fed -Lys·HCl (CLys) or protein-bound Lys in soybean meal (SBM). Thirty-two growing pigs (16 barrows and 16 gilts; average initial BW of 18.6 kg) were used in each of 2 trials. Four pigs (2 barrows and 2 gilts) were euthanized at the start of each trial to determine initial body composition. The remaining pigs were euthanized at the end of the trials to determine empty-body composition and deposition rates of water, protein, fat, ash, and AA. Pigs were randomly allotted to 1 of 7 dietary treatments. There were 2 replications per treatment in each trial for a total of 4 replications. Dietary treatments consisted of a corn-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 CLys. Pigs fed the CLys-supplemented diets at 0.65% SID Lys had more ( < 0.05) body water (663 vs. 624 g/kg) and less ( < 0.01) body protein (153 vs. 160 g/kg) than pigs fed the SBM-supplemented diets. Body fat content decreased ( < 0.01) as the dietary Lys increased similarly for pigs fed Lys from SBM and pigs fed CLys. Gilts had greater ( = 0.05) body Lys content in body protein than barrows (7.68 vs. 7.52 g/100 g). Empty-body ash contents were not different between pigs fed CLys or SBM-supplemented diets. Water deposition and PD increased linearly ( < 0.01) with dietary Lys and were least ( < 0.01) in pigs fed the basal diet but were similar when comparing pigs fed CLys and SBM-supplemented diets at the same dietary Lys concentration. Lysine deposition showed a linear increase ( < 0.01) with dietary Lys but was not different between pigs fed the 2 Lys sources at the same concentration. Barrows and gilts did not differ in tissue deposition rates. Overall, empty-body contents and deposition rates of essential and nonessential AA were not different between pigs fed CLys and pigs fed SBM-bound Lys. The amount of SID Lys required for PD ranged between 0.09 and 0.13 g/g for both sources of Lys. The Lys deposition:SID Lys intake ratio was greater ( < 0.01) in gilts than barrows (0.62 vs. 0.56). Body composition, tissue deposition, and utilization of Lys for PD and Lys deposition were not different in pigs fed diets supplemented with -Lys·HCl with respect to protein-bound Lys in SBM.

A cooperative study on the standardized total-tract digestible phosphorus requirement of twenty-kilogram pigs

A cooperative study comprising growth performance, bone mineralization, and nutrient balance experiments was conducted at 11 stations to determine the standardized total-tract digestible (STTD) P requirement of 20-kg pigs using broken-line regression analysis. Monocalcium phosphate and limestone were added to a corn-soybean meal-based diet at the expense of cornstarch to establish 6 concentrations of STTD P from 1.54 to 5.15 g/kg in increments of 0.62 g/kg at a constant Ca:total P of 1.52:1.0. Diets were fed to 936 pigs (average initial BW of 19 kg) in 240 pens for 20 replicate pens of barrows and 20 replicate pens of gilts per diet. As STTD P increased from 1.54 to 5.15 g/kg of the diet for d 0 to 14, 14 to 28, and 0 to 28, the ADG, ADFI, and G:F increased ( < 0.01). Barrows gained and ate more ( < 0.05) than gilts during d 14 to 28 and 0 to 28. There was no interaction between sex and STTD P concentration for any of the growth performance response criteria. There were both linear and quadratic increases ( < 0.05) in mineral density and content of ash, Ca, and P in the femur expressed as a percentage of dry, fat-free metacarpal as dietary STTD P increased. Furthermore, the maximum load of the femur and mineral density and content and maximum load as well as the Ca and P expressed as a percentage of metacarpal ash linearly increased ( < 0.01) with increasing dietary concentrations of STTD P. There were both linear and quadratic increases ( < 0.01) in apparent digestibility and retention of P with increasing concentrations of STTD P in the diets. Digestibility and retention of Ca linearly ( < 0.01) increased with increasing dietary concentrations of STTD P. Breakpoints determined from nonlinear broken-line regression analyses revealed estimates of 4.20 ± 0.102, 3.20 ± 0.036, or 3.87 ± 0.090 g/kg for ADG during d 0 to 14, 14 to 28, or 0 to 28, respectively. Corresponding estimates using G:F as the response criterion were 4.34 ± 0.146, 3.38 ± 0.139, or 4.08 ± 0.195 g/kg. When mineralization of the femur was used as criteria of response, estimates of STTD P requirement were 4.28, 4.28, or 4.34, g/kg for mineral density, mineral content, or maximum load, respectively. Using mineralization of the metacarpal as criteria of response, estimates of STTD P requirement ranged from 3.5 to 5.0 g/kg depending on the metacarpal response criteria. The study provided empirical estimates of STTD P requirements of 20- to 40-kg pigs.

Energy content of reduced-fat dried distillers grains with solubles for lactating dairy cows

Eight Holstein and 8 Jersey multiparous, lactating cows were used to complete 56 energy balances to determine the energy content of reduced-fat dried distillers grains with solubles (RFDDGS). A repeated switchback design was used to compare treatments with and without RFDDGS. Diets consisted of 24.2% corn silage, 18.4% alfalfa hay, 6.94% brome hay with either 22.9% rolled corn or 14.8% soybean meal (control), or 8.95% rolled corn, 28.8% RFDDGS, and 0% soybean meal [Co-P; dry-matter (DM) basis]. The inclusion of RFDDGS did not affect DM intake, averaging 21.4 ± 0.53 kg of DM for all cows, but milk production tended to increase from 29.8 to 30.9 ± 1.46 kg/d for control and Co-P treatments, respectively. Milk fat percentage and energy-corrected milk did not differ between treatments, averaging 4.33 ± 0.14% and 34.1 kg/d, respectively. Milk protein was significantly decreased by the Co-P treatment (3.56 and 3.41 ± 0.08% for control and Co-P treatments), but protein yield was not affected. Milk energies were 1.40 Mcal/d greater with Co-P. Energy lost as methane was reduced by 0.31 Mcal/d with the addition of RFDDGS to the diet. Heat loss averaged 29.9 ± 0.55 Mcal/d and was not different between diets. Average energy retained as tissue energy was -2.99 ± 0.93 Mcal/d and did not differ between treatments. Intake of digestible and metabolizable energy were not different between the control and Co-P treatments, averaging 2.68 and 2.31 Mcal/kg of DM, respectively. The net energy of lactation values of control and Co-P diets were calculated to be 1.43 and 1.47 Mcal/kg of DM, respectively. These energy estimates suggest greater energy content of diets containing RFDDGS than diets containing a mixture of corn and soybean meal in lactating dairy cows.

Supplementation of organic and inorganic selenium to diets using grains grown in various regions of the United States with differing natural Se concentrations and fed to grower-finisher swine

Grains grown in various regions of the United States vary in their innate or natural Se contents. A regional study evaluated the effects of adding inorganic Se (sodium selenite) or organic Se (Se yeast) to diets with differing innate Se contents. A 2 × 2 + 1 factorial experiment evaluating 2 Se sources (organic or inorganic) at 2 Se levels (0.15 or 0.30 mg/kg) in 18 total replicates (n = 360 total pigs). A basal diet was fed without supplemental Se and served as the negative (basal) control. The study was conducted as a randomized complete block design in 9 states (Georgia, Illinois, Kentucky, Nebraska, North Carolina, Ohio, South Dakota, Texas, and Wisconsin) with each station conducting 2 replicates. Pigs were fed from 25 to approximately 115 kg BW. Similar dietary formulations were used at each station, incorporating a common source of trace mineral and Se premixes. Three pigs per treatment in 16 replicates (n = 240) were bled at 55, 85, and 115 kg BW and serum Se and glutathione peroxidase (GSH-Px) activities were determined. Three pigs (n = 260) from each treatment pen were killed at 115 kg BW and issues (liver, loin, and hair) were analyzed for Se. The corn Se content from the various states ranged from 0.026 to 0.283 mg Se/kg while the soybean meal Se content ranged from 0.086 to 0.798 mg Se/kg. Tissue and serum Se concentrations were greater (P < 0.01) when supplemental organic Se was fed, whereas serum GSH-Px was greater (P < 0.01) as Se level increased. There were linear increases (P < 0.01) in loin and quadratic increases (P < 0.01) in liver and hair Se concentrations as dietary Se level increased within each state. There was a source × level interaction (P < 0.01) for each tissue resulting in a greater increase when organic Se was fed. Serum Se and GSH-Px activity increased (P < 0.01) when both Se sources were fed and plateaued at each state at 0.15 mg Se/kg. There was a high and significant correlation between each tissue Se, serum Se, and GSH-Px activity to dietary Se level indicating that those states having greater grain natural Se contents also had greater tissue Se concentrations. These results indicate that a large difference in corn and soybean meal Se concentrations exists between states, that the addition of organic or inorganic Se to these grains increased tissue and serum Se in each state, and that organic Se was incorporated at greater concentrations in the loin, liver, and hair tissues of grower-finisher pigs than inorganic Se.

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.