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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 (P < 0.05) were assessed using Fisher's LSD procedure. The N intake, fecal N excretion and absorption, and N retention increased (P < 0.05) in pigs fed high-CP diets with added fiber (HP vs. HPBR). With added fiber, urinary N excretion (g/d) was reduced (P < 0.02) only for the low-CP diet. Urinary N as a percentage of N intake was reduced (P < 0.01) 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 (P < 0.02) 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.

The effect of environmental heat stress on N metabolism was studied using 7 gilts (50.5 ± 1.7 kg initial BW). Pigs were housed in metabolism cages in a climate-controlled room. After a 4-d adaptation, two 14-d experimental periods followed during which the animals were exposed to thermo-neutral temperature (NT; 20.61 ± 0.1°C) or high environmental temperature (HT; 30.41 ± 0.4°C). In each experimental period, two 24-h balance periods were carried out to collect feces and urine (via bladder catheters) for N analysis. Based on N intake and N excretion, N balance was calculated. At HT conditions, N intake was lower (P = 0.028), urinary N excretion increased (P = 0.040), and N retention decreased (P = 0.001) in comparison with NT conditions. Exposure of pigs to HT tended to reduce (P = 0.070) digestibility of N as compared to NT conditions. When pigs are exposed long term to continuous HT, N retention decreases presumably due to decreased use of ME during respiration.

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 (P < 0.001) in WDG (71.8%) and lowest (P < 0.001) 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.