Abstract The study was to evaluate the effect of premix carriers rich in iron (sand), calcium (limestone), or fiber (rice hull) on growth performance of early-growing pigs. A total of 215 pigs [initial body weight (BW) = 39.90 ± 5.06 kg) were randomly allotted to 3 dietary treatments containing 2% of different premix carriers: sand, limestone, or rice hull (30% crude fiber) using initial BW and sex as blocks (5 to 6 pigs per pen, 14 pens per treatment). The total Ca in sand, limestone, and rice hull were 4.28, 39.52, and 0.27 %, respectively, with Fe levels of 2.39, 0.20, and 0.05%, respectively. The analyzed total Ca level of the experimental diet containing sand, limestone, or rice hull was 0.69, 0.71, or 1.88 %, the analyzed total P level was 0.49, 0.49, or 0.48 %, and the analyzed total Fe level was 305, 633, or 347 ppm, respectively with 144 ppm of Fe from FeSO4·H2O in each diet. During the 28 d of the experiment, BW, feed disappearance, and fecal scores (ranging from 0 to 3 with 3 indicating watery feces) were recorded. Blood and feces were collected at the end of the experiment to measure the ATTD of dry matter (DM) and CP, serum iron concentration, hemoglobin, and red blood cell count. Data were analyzed by ANOVA using the Mixed Procedure of SAS with different premix carriers as the fixed effect. Limestone reduced the average daily gain (ADG; P < 0.05, 0.871 vs. 0.965 and 0.935 kg/d), increased feed conversion ratio (FCR; P < 0.05, 2.55 vs. 2.33 and 2.36), and aggravated diarrhea severity as reflected by greater fecal scores (P < 0.05, 1.53 vs. 1.18 and 1.19) compared with sand and rice hull as carriers. The ATTD of both DM and CP in pigs fed a premix with sand as a carrier were greater than that in rice hull- or limestone-treated pigs (P < 0.05, DM: 86.7 vs. 77.7 or 74.1%; CP: 86.1 vs. 75.0 or 73.3%). Furthermore, pigs fed a premix containing sand exhibited the greatest serum iron concentrations among treatment groups (sand, limestone, and rice hull: 2.81, 1.93, and 1.69 mg/L). However, no significant difference was observed in red blood cell count or hemoglobin concentrations among groups. In sum, excessive limestone in premix can negatively affect growth performance and fecal consistency, whereas using sand rich in iron as a carrier in premix exerted minimal impact on nutrient digestibility as opposed to limestone or rice hull.
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