The effect of high-fiber diets on nutrient utilization and intestinal morphology of growing pigs
Three balance experiments were conducted to determine the effects of dietary fiber on mineral balance and intestinal.morphology of growing pigs. Fiber sources were added to corn-soybean meal diets at levels which increased neutral-detergent fiber levels by 6 to 8%. In experiment 1, 10% oat hulls (OH) decreased Ca (P<.06) and Zn (P<.01) balances of pigs after a 7 d feeding period. Wheat bran (20%) increased Mg intake and balance (P<.02), but did not affect Ca and Zn balances. In experiment 2, pigs were fed diets (with or without supplements of Zn, Fe and Mg) containing 15% OH or soybean hulls (SH) for 5 d or 26 d. SH increased Fe intake and balance (P<.01) and ( Mg absorption (P<.01). Compared with balances at 5 d, Zn balance was similar, while Fe and Mg balances were higher at 26 d for pigs fed the basal (P<.05) or SH (P<.01) diets. However, Zn balance was lower (P<.05) at 26 d 1 but Fe balance did not change over time for pigs fed the OH diets. At each time period, Zn balance was not different between pigs fed the basal or high-fiber diets. In experiment 3, Ca, Zn and Mg absorption were not affected by 15% OH or SH or 20% alfalfa meal (AM) after 67 d or 39 d, although SH and AM increased Fe balance (P<.01). Intestinal surface morphology of 12 pigs fed in experiment 3 was examined by scanning electron microscopy. Villus morphology was variable in jejunum, ileum and colon, although evidence of villus blunting and folding accompanied by erosion of microvilli and loss of epithelial cells was observed in small intestine of some pigs fed the SH and AM diets. Damage was not consistent in all sites examined in individual pigs, and did not occur in all pigs fed any specific diets. Although Ca and Zn balances were decreased by OH in two of the balance trials, the inability of OH to consistently decrease mineral balance suggests that the ability of the pig to adapt to different diets may be sufficient to overcome the mild inhibitory effect on mineral absorption of some fiber sources. When viewed together, the results of the balance trials indicate that moderate amounts of dietary fiber have a minimal negative impact on mineral balance of pigs fed practical corn-soybean meal diets. However, the results also indicate that fiber sources such as SH and AM, are rich sources of some minerals for the pig, particularly Fe. Evidence of intestinal damage was evident in pigs fed the high-fiber diets. However, not all animals fed a particular diet were affected, which suggests that some pigs within a given population may be susceptible to detrimental effects of dietary fiber on intestinal structure or function.