The Effect of Xylose on Water and Energy Balance in Pigs

To improve carbohydrase efficacy, an understanding of the utilization and energetic contribution of the xylanase hydrolysis product, xylose, is needed. The objective of this experiment was to determine the effects of dietary xylose concentration and adaptation time on water and energy balance and urinary xylose excretion. Forty-eight pigs were randomly assigned to 1 of 4 dietary treatments with increasing levels of D-xylose (n=12/treatment) in 2 replications of a 21-d experiment with 3 collection periods. The control diet was xylose-free (CON); the remaining treatments consisted of 2% (X2), 4% (X4), or 8% (X8) D-xylose added to CON. Pigs were limit fed and housed in metabolism crates. The effects of adaptation time were assessed by utilizing 3 fecal and urine collection periods at which time water intake was also measured. Collection period 1 (C1) was d 5-7, C2 was d 12-14, and C3 was d 19-21. Growth performance was calculated based on BW measured on d 0 and 21. Diets, feces, and urine were analyzed for xylose concentration and GE. Data were analyzed using SAS with treatment and collection period as fixed effects and replication as a random effect. The interactions of treatment by collection were analyzed using repeated measures. The average initial BW was 28.26±0.46 kg and ADG and G:F did not differ due to treatment (P>0.10). As dietary xylose concentration increased, water intake increased linearly from 2447 ml/d in CON to 3017 ml/d in X8 (P<0.05). Similarly, water intake:feed intake ratio and urine output increased linearly (P<0.05). Water balance differed across collection periods with pigs consuming more water and excreting more urine during C1 vs. C2 and C3 (P<0.05). Water waste was also greater in C1 vs. C2 and C3 (1404 ml/d vs. 712 and 837 ml/d; P<0.05). As dietary xylose concentration increased, urine xylose concentration, urine GE, and the percent of urine GE from xylose increased linearly (P<0.05). During C1 the percent of xylose consumed that was excreted in the urine decreased as dietary xylose concentration increased (treatment*collection period P<0.05). However, this effect diminished at C2 and was not apparent at C3, indicating that at low xylose concentrations (2 and 4%) pigs can adapt to utilize xylose more efficiently. The efficiency of X8 was similar across all collections. In conclusion, increasing dietary D-xylose clearly increases water intake and urinary output and increases urinary xylose and GE excretion, but pigs may possess adaptive mechanisms to more efficiently utilize xylose.