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The effect of dietary CP level on performance, enteric health, and gastrointestinal microbial ecology of weaned pigs challenged with enterotoxigenic Escherichia coli (ETEC) K88 was investigated in a 14-d study. Forty weaned pigs (BW = 5.32 [+ or -] 0.24 kg, mean [+ or -] SD), housed 4 per pen, were randomly assigned to 2 diets (5 pens/diet): 1) 22.5% CP or 2) 17.6% CP supplemented with AA. Diets contained the same amount of ME and standardized ileal digestible Lys, Met + Cys, Thr, and Trp based on the ideal protein ratio. Isoleucine and Val were added to the 17.6% CP diet up to the level in the 22.5% CP diet. On d 8 postweaning, pigs were challenged with 6 mL of ETEC suspension ([10.sup.10] cfu/mL) by garage. Feed disappearance and BW were measured on d 7, 9, 10, 12, and 14 for determination of ADG, ADFI, and G:F. One pig from each pen was serially slaughtered on -1, 3, and 7 d postchallenge (10 pigs/d of slaughter) to evaluate gut morphology, and gut microbial ecology and metabolites. Pigs fed the 22.5% CP diet had greater (P < 0.05) ADG and G:F than those fed the 17.6% CP diet before infection, but performance was similar between the 2 diets after ETEC challenge and overall. On d 3 after challenge, ETEC was not detected in the ileal digesta of pigs fed the 17.6% CP diet but was detected in the ileal digesta of 80% of pigs fed the 22.5% CP diet (5.22 [+ or -] 1.07 cfu/g, mean [+ or -] SD). Pigs fed the 17.6% CP diet had a greater (P < 0.01) prevalence of order Clostridiales (73 vs. 50%), family Lachnospiraceae (43 vs. 18%), and genus Roseburia (13 vs. 3%) in the colon digesta 7 d after challenge compared with those fed the 22.5% CP diet. The richness and diversity of bacteria in the colon digesta were less (P < 0.05) in pigs fed the 17.6% CP diet than in those fed the 22.5% CP diet at -1, 3, and 7 d postchallenge. Pigs fed the 22.5% CP diet had greater (P < 0.05) ammonia N concentration in the colon digesta on -1 and 7 d after challenge compared with those fed the 17.6% CP diet. Pigs fed the 22.5% CP diet had deeper (P < 0.05) crypts 1 d before challenge, shorter villi 3 d after challenge, and reduced villus height:crypt depth 1 d before and 3 d after challenge compared with those fed the 17.6% CP diet. In conclusion, a reduction in the dietary CP level of weaned pigs from 22.5 to 17.6% with AA supplementation impaired growth performance before, but not after, the ETEC challenge and increased the relative composition of butyrate producing bacteria in the colon digesta after ETEC challenge. Key words: Escherichia coli K88, gut ecology, performance, protein, weaned pig

Although AA requirements for the mean of a population of growing pigs have been established using traditional methods, there are no estimates of the variability within the population and whether this variation differs among AA. With the increased use of supplemental Lys in pig diets, there will be an increased need to supplement Met, commonly the second or third limiting AA in corn-soybean diets. The indicator AA oxidation method allows repeated measurements in a short period of time so that the AA requirement can be determined for individual pigs at a similar physiological stage. The objective of this study was to determine the mean Met requirement in individual gilts and to estimate the related variability. Six individually housed female pigs (initial BW = 8.8 kg, SD 1.5) each received diets providing 6 levels Of DL-Met. The isonitrogenous and isoenergetic diets contained 0.187, 0.250, 0.290, 0.320, 0.350, and 0.377% Met (analyzed, as-fed basis). Cysteine (0.48%) and Lys (1.44%) concentrations were similar for all diets. Pigs were adapted for 6 d to the basal corn-soybean meal diet (0.187% Met), which was offered at 95 g/[kg.sup.0.75] of BW to ensure complete consumption of the test diets. During 4-h oxidation studies, 313.4 kBq, (SD 35.6) of L-[1[sup.14]C]Phe was mixed with each of 8 half-hourly meals, and expired C[O.sub.2] was collected. The breakpoint in Phe oxidation, representing the Met requirement, and its variability, was determined using 2-phase linear regression. Phenylalanine oxidation decreased as the Met content increased from 0.187 to 0.29%. Phenylalanine oxidation was not different (P > 0.2) for diets ranging from 0.320 to 0.377% Met. The dietary Met requirement varied from 0.320 to 0.373% for individual pigs. The mean Met requirement for individual pigs was determined to be 0.340% of diet (SD = 0.024%, CV= 7.1%), with 0.340, 0.364, and 0.388% covering the requirement of 50, 66, and 95% of the population, respectively. The present mean population estimate was similar to the recommended dietary Met concentration of 0.325% for pigs of this BW and feed intake. To maximize profitability, Met levels in starter pig diets should be determined, depending on the cost of crystalline Met and the fraction of the population whose requirement is to be met. Key words: gilt, indicator amino acid oxidation, methionine, requirement, variability

Diarrhea incidence in weaned pigs may be associated with the concentration of intestinal microbial metabolites (ammonia, amines, and VFA) that are influenced by dietary CP content. Three experiments were conducted to determine effects of a low-protein, AA-supplemented diet on ileal AA digestibility, growth performance, diarrhea incidence, and concentration of microbial metabolites in ileal and cecal digesta of pigs weaned at 14 d of age. In Exp. 1, 8 pigs fitted with a simple T-cannula at the distal ileum were assigned in a crossover design to 2 diets containing 24 or 20% CP using wheat, corn, full-fat soybeans, whey powder, fish meal, and blood plasma as the main ingredients. Supplemental AA were added to the diets to meet the AA standards according to the 1998 NRC recommendations. Chromic oxide was used as an indigestible marker. Diets were fed at 2.5 times the ME requirement for maintenance. The reduction of dietary CP decreased (P < 0.05) the apparent ileal digestibility of most AA, except Lys, Met, Thr, Val, and Pro. Dietary CP content did not affect the pH of ileal digesta or ileal concentrations of ammonia N, cadaverine, putrescine, or VFA. In Exp. 2, 8 pigs fitted with a simple T-cannula in the cecum were assigned to 2 diets, similar to Exp. 1. Dietary CP content did not affect the pH of cecal digesta. The reduction in CP content decreased (P < 0.05) cecal ammonia N, acetic acid, isobutyric acid, isovaleric acid, total VFA, and putrescine concentrations by 28 to 39%. In Exp. 3, 32 pigs were assigned to 2 diets, similar to Exp. 1, according to a randomized complete block design. Pigs had free access to feed and water. Dietary CP content did not affect growth performance or fecal consistency scores during the 3-wk study, and diarrhea was not observed. The results of these experiments indicate that lowering the dietary CP content combined with supplementation of AA markedly reduced the production of potentially harmful microbial metabolites in cecal digesta of early-weaned pigs without affecting growth performance. Key words: amino acid, digestibility, early-weaned pig, growth, microbial metabolite, protein

The effects of low-protein AA-supplemented diets on piglet performance, visceral organ mass, incidence of diarrhea, intestinal microbial population, and fermentation were studied in a 3-wk trial. After a 7-d adaptation period, 96 piglets (~6.2 kg of initial BW) were assigned to 4 corn-wheat, soybean meal-based dietary treatments in a completely randomized design to give 6 replicate pens per treatment (n = 4 piglets per pen). The treatments were a control wheatcorn-soybean meal-based phase I diet containing 23% CP, or the same diet with CP reduced to 21%, 19%, or 17% and supplemented with crystalline AA to achieve equal standardized ileal digestible contents of Lys, Met plus Cys, Thr, and Trp in all diets. Diets were formulated to similar nutrient levels and provided ad libitum. Blood from all pigs was taken on d 0, 7, 14, and 21 for determining plasma urea N. Weekly feed intake, BW changes, and G:F were determined. On d 21, 2 pigs per pen were randomly selected and killed to determine small intestinal morphology, digesta pH and ammonia levels, and luminal microbial counts. Average daily feed intake, ADG, and G:F were not affected (P > 0.10) by reducing CP to 21%, but a reduction to 19% or 17% decreased ADFI (P < 0.001) and ADG (linear, P < 0.001; quadratic, P < 0.05) over the 3-wk study period. Reducing CP to 19% had no effect (P > 0.10) on G:F; however, this response criterion was decreased linearly (P < 0.001) over the 3-wk study period as dietary CP declined. Water usage was only numerically decreased (P > 0.10) with dietary CP reduction. Plasma urea N was decreased linearly (P < 0.01) with CP reduction. Reducing CP from 23 to 17% had a linear (P < 0.05) and cubic effect on stomach and liver weights, respectively. Although histological data showed some differences among diets, no distinct trend was evident. Ammonia N in ileal digesta was reduced linearly (P < 0.01) as dietary CP was decreased. With the exception of valeric acid, VFA levels in ileal digesta of piglets fed low-protein diets were generally lower (P < 0.05) compared with the control diet. Diet had no effect on intestinal microbial counts (P > 0.10). The results show that piglet performance may suffer when dietary CP is reduced by 4 or more percentage units from 23% and support the hypothesis that low-CP diets help maintain enteric health in pigs by lowering toxic microbial metabolites such as ammonia. Key words: amino acid, protein, early-weaned pig, growth, intestinal health

Two experiments were conducted to evaluate the efficacy of dietary DL-methionine hydroxy analog-free acid (MHA-FA, 88%) compared with DL-methionine (DLM, 99%) as Met sources in pigs. In Exp. 1, a total of 245 crossbred pigs (initial BW of 6.4 kg [SD = 0.5]) were allotted to 7 treatments in 7 replicates for an experimental period of 28 d. The basal diet (BD)was formulated to contain 17.5% CP and 0.21% Met. Dietary treatments included 1) BD, 2) BD + 0.030% DLM, 3) BD + 0.060% DLM, 4) BD + 0.090% DLM, 5) BD + 0.034% MHA-FA, 6) BD + 0.068% MHA-FA, and 7) BD + 0.103% MHA-FA; the MHA-FA was supplemented on an equimolar basis to the DLM. Because of a nonlinear response, exponential regression analysis was used to evaluate the responses, and a comparison of the equations was then made to determine the relative effectiveness of the 2 Met sources. With increases in dietary Met, weight gain increased (P < 0.05). Compared with DLM on a product-to-product (wt/wt) basis, the relative effectiveness of MHA-FA was calculated to be 73% for increasing weight gain and 54% for decreasing the feed:gain. In Exp. 2, a total of 30 weanling barrows [initial BW of 16.8 kg(SD = 2.8)] were used in a metabolism study to evaluate the relative value of MHA-FA to DLM. The BD was formulated to contain 16.9% CP and 0.21% Met. Dietary treatments included 1) BD, 2) BD + 0.030% DLM, 3) BD + 0.060% DLM, 4) BD + 0.046% MHA-FA, and 5) BD + 0.092% MHA-FA; the MHA-FA levels were chosen based on a pre-experiment estimate of bioequivalence in an attempt to provide approximately equal pig responses. There was no difference in fecal N output among the treatments; however, urine N linearly decreased with increasing concentrations of both sources (P = 0.034 for DLM, and P = 0.007 for MHA-FA), which resulted in a linear increase in retained N for both DLM (P = 0.012) and MHA-FA (P = 0.005). In addition, N retention (% of intake) linearly increased with increasing level of DLM (P = 0.014) and MHA-FA (P = 0.007). Using a slope-ratio procedure for comparison of the responses from the 2 sources, the relative biological equivalence value of MHA-FA to DLM in this experiment was 64.2% based on percent N retention and 66.3% based on the grams of N retained per day. Based on the results from both experiments, these data indicated that the mean relative bioequivalence of MHA-FA to DLM was 64% on a product-to-product (wt/wt) basis or 73% on an equimolar basis. Key words: bioefficacy, methionine, methionine hydroxy analog, pig

Two N balance studies were conducted to investigate the effects of feeding graded levels of pectin (a soluble nonstarch polysaccharide, NSP) on the utilization of ileal digestible threonine (Thr; Thr study) and lysine (Lys; Lys study) intake for body protein deposition (PD) in growing pigs. In each study, eight Yorkshire barrows with an average initial BW of 17.2 [+ or -] 1.3 (Thr study) and 14.3 [+ or -] 1.4 kg (Lys study) were fed each of five experimental diets during five subsequent experimental periods, according to a crossover design. Pigs were fed twice daily at 2.6 times maintenance energy requirements. The soybean- and cornstarch-based diets, in which either Thr or Lys was the first-limiting nutrient, were formulated to contain (as-fed basis) 0, 4, 8, or 12% pectin or 8% cellulose (water-insoluble NSP), respectively, and with NSP substituting cornstarch. Across treatments, the mean daily Thr and Lys intake were 5.42 [+ or -] 0.04 g/d (Thr study) and 7.98 [+ or -] 0.12 g/d (Lys study), respectively. Apparent and standardized ileal digestibilities of Thr and Lys were determined in a separate study. Mean PD was 93.4, 90.2, 82.1, 76.7, and 87.9 g/d (SEM = 1.3; Thr study) and 90.7, 88.6, 87.8, 85.3, and 88.1 g/d (SEM = 1.1; Lys study) for the five respective treatments. Utilization of ileal digestible Thr intake, but not of ileal digestible Lys intake, for PD decreased linearly with dietary pectin level, and was not influenced by diet cellulose level. The current study indicates that apparent and standardized ileal digestibility values do not provide an accurate predictor of dietary effects on the utilization of ileal digestible Thr intake for protein deposition in growing pigs fed diets containing soluble NSP. Key Words: Lysine, Nonstarch Polysaccharides, Pectin, Pigs, Protein Deposition, Threonine

A pig growth assay was conducted to determine the relative biological value (RBV) of lysine from L-lysine sulfate compared with feed-grade L-lysine*HCl. One hundred nursery pigs with an average initial BW of 9.5 [+ or -] 1.5 kg were blocked by BW and gender and allotted randomly to five dietary treatments in five replicates of four pigs per pen. A corn-peanut meal diet containing 0.6% total lysine (as-fed basis) was supplemented with two levels (0.1 and 0.2%) of lysine from L-lysine*HCl or L-lysine sulfate. The RBV of L-lysine sulfate was determined using multiple regression slope-ratio methodology, with ADG and G:F as the response criteria. At the tested levels, linear responses for gain and G:F were obtained from increments of lysine from the two lysine sources. When ADG was regressed on supplemental lysine intake, the RBV of lysine in L-lysine sulfate was 99% of the RBV of lysine in L-lysine*HCl. When G:F was regressed on supplemental lysine intake, the RBV of lysine in L-lysine sulfate was 97% of the RBV of lysine in L-lysine*HCl. The t-test analysis revealed that the RBV of lysine in L-lysine sulfate was not significantly different from the RBV of lysine in L-lysine*HCl, which was assumed to be 100% bioavailable. In conclusion, L-lysine sulfate can replace L-lysine*HCl in diets for growing swine. Key Words: L-Lysine*HCl, L-Lysine Sulfate, Pigs, Relative Bioavailability

Reproductive performance is steadily increasing within the pork industry; logically, amino acid requirements need to be redefined for sows producing larger litters. The objective of this study was to determine the threonine requirement of the high-producing lactating sow and to determine the effect of lysine on this requirement. A total of 419 PIC C-15 sows were assigned randomly to treatment within parity groups (1, 2, and 3+) and gestation treatment at d 110 of gestation. Lactation diets were formulated to contain 0.80% total lysine (tLYS) with 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, or 0.65% total threonine (tTHR) or 1.06% tLYS with 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, or 0.70% tTHR. Litters were standardized to a minimum of 11 piglets within 48 h after farrowing, and sows had free access to feed throughout lactation (lactation length = 20.1 [+ or -] 0.1 d). Sow ADFI exceeded expectation, averaging 6.90, 7.40, and 7.20 kg/d for Parities 1, 2, and 3+, respectively. Daily tLYS intake was 58 g/d (47 g of apparent ileal digestible lysine [dLYS] per day) and 74 g/d (59 g dLYS/d) for the low- and high-lysine group, respectively. Lysine intake did not affect sow or litter performance (P [is greater than] 0.10). Sows gained an average of 4.8 kg in lactation. Using regression analysis, BW gain was maximized at 0.54% tTHR for all parity groups (quadratic; P [is less than] 0.05). Litter weaning weight (67.1, 67.9, and 66.2 kg for Parities 1, 2, and 3+, respectively) and litter weight gain (2.49, 2.53, and 2.44 kg/d for Parities 1, 2, and 3+, respectively) were maximized at 0.53% tTHR using regression analysis, for all parity groups (quadratic; P [is less than] 0.05). Based on regression analysis, plasma urea nitrogen on d 10 and 18 was minimized at 0.54% tTHR (P [is less than] 0.05). Lysine levels in excess of 58 g of tLYS/d did not benefit sow or litter performance. The requirement for threonine to minimize sow tissue mobilization was 37, 40, and 38 g tTHR/d (28, 30, and 30 g of apparent ileal digestible threonine [dTHR] per day) for Parities 1, 2, and 3+ sows, respectively. The threonine required to maximize litter performance was 36, 39, and 38 g of tTHR/d (28, 30, and 29 g of dTHR/ d) for Parities 1, 2, and 3+ sows, respectively. Alternatively, the requirement can be expressed as 14.3 g tTHR (11.8 g dTHR) per kilogram of litter gain. Key Words: Lactation, Lysine, Sows, Threonine

Nutrient intake during gestation has an impact on gestation parameters and subsequent lactation performance. The objectives of this experiment were to determine the impact of feeding two levels of amino acids in gestation on sow BW changes in gestation and lactation, and litter size, and to evaluate a factorial method for determining daily energy requirements. At mating, 419 sows (Camborough 15; Pig Improvement Canada, Acme, AB) were assigned randomly within Parities 1, 2 or 3+ to a gestation diet containing either 0.44% (low lysine) or 0.55% (high lysine) total lysine and 3,100 kcal DE/kg; other indispensable amino acids were adjusted to lysine based on ideal protein ratios. Feed allowance in gestation was determined factorially using estimated DE requirements for maintenance, maternal gain, and conceptus growth. Sows were allowed free access to the lactation diet. Gestation BW gain from d 0 to 110 was affected by parity (61.2, 60.0, and 42.3 kg for Parity 1, 2, and 3+, respectively; P [is less than] 0.05) but not (P [is greater than] 0.10) by gestation lysine level. Sow BW changes from d 0 of lactation to weaning were affected by parity (0.5, 6.8, and 5.8 kg for Parity 1, 2, and 3+, respectively; P [is less than] 0.01) and gestation BW gain (P [is less than] 0.01), but not by gestation lysine level (5.0 vs 3.8 kg for low and high lysine, respectively; P [is greater than] 0.10). Total piglets born was affected by parity (11.5, 12.1, and 12.5, for Parity 1, 2, and 3+, respectively; P [is less than] 0.01) and increased with increasing sow BW gain (P [is less than] 0.05). Total piglets born alive (mean = 11.2) was increased with increasing sow BW gain (P [is less than] 0.05). Total litter weight born alive was affected by parity (15.9, 18.6, and 19.4 kg for Parities 1, 2, and 3+, respectively; P [is less than] 0.01) and gestation BW gain (P [is less than] 0.05). The model used to determine daily energy intake requirements resulted in an average BW gain of 10.6 kg above the targets set by the model. Total lysine intakes greater than 10.6 g/d in gestation did not improve sow productivity. Setting target weight gains in gestation and feeding to meet these targets may not always provide predictable results due to a number of factors that affect the energy requirement in the sow. Key Words: Sows, Amino Acids, Energy, Gestation