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Two experiments were conducted to study the effects of inclusion of additional fiber in the Phase I diet on growth performance and nutrient digestibility in piglets reared under "optimal" or "poor" hygienic conditions. In both experiments, the design was completely randomized with a control diet that contained 2.2% crude fiber and 8 additional isonutritive diets that included 2.5 or 5.0% of sugar beet pulp (SBP), straw, oat hulls (OH), or wheat middlings (WHM). Preplanned polynomial contrasts were used to study the effects of 1) fiber inclusion (control diet vs. average of the 8 fiber-containing diets), 2) source of fiber, 3) level of fiber, and 4) interaction between source and level of fiber. In Exp. 1 (clean barn), fiber inclusion increased ( < 0.01) the incidence of postweaning diarrhea (PWD) and reduced ( < 0.05) feed efficiency and apparent total tract digestibility (ATTD) of all nutrients except that of CP, which was not affected. Piglet performance was not affected by source or level of dietary fiber. The ATTD of all nutrients decreased ( < 0.05) as the level of fiber increased and was lower in pigs fed straw or OH than in pigs fed SBP or WHM. The apparent ileal digestibility of GE and DM decreased ( < 0.05) with fiber inclusion, a reduction that was more pronounced ( < 0.05) with straw or SBP than with OH inclusion, with WHM inclusion being intermediate. Fiber inclusion did not affect villous height to crypt depth ratio of the ileum mucosa. The inclusion of 5% of a fiber source increased and counts in the cecum ( < 0.001) but the to ratio was not affected. In Exp. 2 (dirty barn), fiber inclusion did not affect piglet performance but tended to increase PWD ( = 0.07). Also, fiber inclusion reduced ( < 0.05) the ATTD of all dietary components except that of CP, which was not affected. Source and level of fiber did not affect ATTD of nutrients except for DM, which was greater for pigs fed SBP than for pigs fed straw ( < 0.05). In conclusion, in the current research, pigs reared under optimal hygienic conditions had lower incidence of PWD, better growth performance, and greater DM and GE digestibility than pigs reared under poor hygienic conditions. An excess of dietary fiber was more detrimental for all these traits in piglets reared under optimal hygienic conditions. The effects of the source and level of fiber on piglet performance was limited in the 2 experiments.

The influence of CP content and ingredient complexity, feed form, and duration of feeding of the Phase I diets on growth performance and total tract apparent digestibility (TTAD) of energy and nutrients was studied in Iberian pigs weaned at 28 d of age. There were 12 dietary treatments with 2 type of feeds (high-quality, HQ; and low-quality, LQ), 2 feed forms (pellets vs. mash), and 3 durations (7, 14, and 21 d) of supply of the Phase I diets. From d 7, 14, or 21 (depending on treatment) to d 35, all pigs received a common diet in mash form. Each treatment was replicated 3 times (6 pigs/pen). For the entire experiment, ADG (P 0.10) by feed quality, but feeding pellets or increasing the duration of feeding the Phase I diets improved G:F (P < 0.01). Also, in this period, PWD was greater with pellets than with mash and for pigs fed the Phase I diets for 14 or 21 d than for pigs fed the diet for only 7 d (P < 0.01). From d 21 to 35, pigs previously fed the LQ diet had greater ADG than pigs fed the HQ Phase I diets (P < 0.001). Also, pigs fed the Phase I diets for 21 d had decreased ADG (P < 0.05) and ADFI (P < 0.001) and reduced G:F (P < 0.05) than pigs fed these diets for 7 or 14 d. Organic matter digestibility was greater for pigs fed the HQ Phase I diets than pigs fed the LQ Phase I diets (P < 0.05). Pelleting improved TTAD of all nutrients (P < 0.01). It is concluded that HQ Phase I diets increased TTAD of nutrients but not feed efficiency of Iberian pigs from d 0 to 35. Also, pelleting improved energy and nutrient digestibility and feed efficiency. Increasing the duration of supply of the Phase I diets from 7 to 21 d improved feed efficiency but reduced ADG. Therefore, the use of LQ Phase I diets in pellet form for no more than 7 d after weaning is recommended in Iberian pigs.