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Nitrogen (N) balance experiment was carried out to study the individual and group response of growing pigs to lysine (Lys) intake. A series of 15 purified diets limiting in Lys were fed sequentially to nine pigs (initial body weight, 39 kg) during a 15-day experiment. Lysine concentration ranged from 50% to 140% of its assumed requirement. N retention in individual pigs was related to Lys intake using linear-plateau (LP) and quadratic-plateau (QP) models. No difference in the closeness of fit between the models was found (p = 0.72). There were significant differences between the slopes of individual regression lines in the LP model (p = 0.018) and between the individual plateau values in both models (p < 0.0001). The breakpoint values in the QP model were greater than those of the LP model (p = 0.027), while the plateau values estimated by both models were similar (p = 0.32). In the LP model, no relationship was found between the slopes and plateau values (p = 0.67, r = 0.17) or between the slopes and breakpoint values (p = 0.55, r = -0.23), thus suggesting that pigs with higher protein deposition rate do not utilize lysine more efficiently. However, there was a close positive correlation between breakpoint and plateau values (p = 0.0005, r = 0.92). Based on LP and QP models, the mean daily requirement of Lys for a 47-kg gilt was estimated to be 20.8 and 24.2 g (0.79 and 0.92 g/MJ metabolizable energy), respectively, with coefficients of variation of approximately 10%. Marginal efficiency of Lys utilization derived from the LP model was 0.67 and was dependent on the range of input data selected. Lysine disappearance was a curvilinear function of Lys intake, indicating that Lys catabolism is not directly related to Lys intake. The closeness of fit of exponential, saturation kinetics or four-parameter logistic models applied to data set of all pigs was similar to that of LP or QP models.

Eight gilts (29.9 ± 1.7 kg initial BW) were used to evaluate effects of dietary (crude) fiber on N excretion via feces and urine at 2 levels of dietary CP. Pigs were fed 4 dietary treatments according to a double 4 × 4 Latin square. Treatments were low (14%) CP and low (3.25%) (crude) fiber (LPAA), low CP and high (4.46%) fiber (LPAABP), high (18.8%) CP and low fiber (HP), and high CP and high fiber (HPBP). Diets were based on soybean (Glycine max) meal, wheat (Triticum aestivum), and maize (Zea mays) and were supplemented with crystalline AA. High fiber diets contained 15% dried beet (Beta vulgaris) pulp. Pigs were housed in metabolic cages and fed 2 equal meals at 0700 and 1700 h at a daily rate of 90 g/kg BW(0.75). Water was offered ad libitum. Each experimental period consisted of a 6-d adaptation followed by a 4-d collection of feces and urine (bladder catheters). Data were analyzed using ANOVA. Differences between means (P0.05) were assessed using Fisher's LSD procedure. The N intake, fecal N excretion and absorption, and N retention increased (P0.05) in pigs fed high-CP diets with added fiber (HP vs. HPBR). With added fiber, urinary N excretion (g/d) was reduced (P0.02) only for the low-CP diet. Urinary N as a percentage of N intake was reduced (P0.01) in both groups fed high-fiber diets irrespective of dietary CP content. Dietary fiber level did not affect DMI. Fecal DM excretion (g/d) was higher (P0.02) in pigs fed diets with high CP and high fiber content than in pigs fed diets with high CP and low fiber content. In conclusion, beet pulp fiber added to diets increased fecal N and reduced urinary N and in diets with higher CP content increased overall N retention.

Chemical composition and nutrient and energy digestibilities were determined in 4 samples of dried distillers grains with solubles (DDGS) and 1 sample of wet distillers grains (WDG) from 4 ethanol fuel manufacturers. The cereal sources used for ethanol production were wheat (Triticum aestivum; 1 sample), wheat + barley (Hordeum vulgare; 2 samples), and maize (Zea mays; 2 samples). The nutrient contents (expressed as % of DM) were variable, ranging from 30.5 to 39.5 CP, 4.4 to 12.3 fat, 7.5 to 12.9 crude fiber, 2.7 to 7.8 ash, and 0.4 to 0.9 total P. The concentration of Lys ranged from 2.05 to 5.20 g/kg DM. The diets were fed to 6 gilts (39.9 ± 1.9 kg BW) fitted with ileal T-cannulas using a 5 × 6 Youden square. Each experimental period comprised a 5-d adaptation followed by a 2-d collection of urine and feces and 1-d (24 h) collection of ileal digesta. Using acid-insoluble ash as a marker, apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients and energy and AID of AA were calculated. The ATTD of N ranged from 55.7 to 83.7%. The N retention expressed as percentage of N intake ranged from 10.2 to 32.0. Except for wheat-based DDGS, the AID of N was 66.8%. The ATTD and AID values of NDF were 52.8 and 24.4%, respectively. The concentration of total P in WDG was half of values in DDGS, which likely caused its very low ATTD (1.4%). The ATTD and AID of energy ranged from 58.8 to 73.9% and from 40.6 to 54.1%, respectively. The AID of AA was greatest (P0.001) in WDG (71.8%) and lowest (P0.001) in DDGS from wheat (44.8%). In conclusion, nutrient variability among DDGS samples varies greatly, and source of origin is an important determinant of quality.

Summary Two N balance experiments were conducted to study the individual response of growing pigs to limiting amino acid (AA) intake. Series of fifteen diets with increasing concentration of sulphur amino acids (SAA, Expt 1) or methionine in the presence of excess cystine (Expt 2) were fed sequentially to nine pigs during a 15-day experimental period. The concentration of the AA under test ranged from 50% to 140% of the requirement while other essential AA were given in a 25% excess relative to the limiting AA. N retention was related to the limiting AA intake using rectilinear and curvilinear models. In Expt 1, the quadratic-plateau model fitted the individual data significantly better (p = 0.01) than the linear-plateau model. No difference was found between the two models in Expt. 2, presumably due to the sparing effect of excess cystine on methionine utilization. Exponential, saturation kinetics or four-parameter logistic models fitted to data for all pigs showed that their goodness of fit was similar to those of quadratic-plateau or linear-plateau models. Significant differences (p