BackgroundSmall peptide chelated iron (SPCI), a novel iron supplementation in pig diets, owns growth-enhancing characteristics. Although a number of researches have been performed, there is no clear-cut evidence to show the exact relationship between the dose and effects of small peptide chelated minerals. Therefore, we investigated the effect of dietary supplementation of SPCI at different doses in the growth performance, immunity, and intestinal health in weaned pigs.MethodsThirty weaned pigs were randomly assigned into five groups and feed with basal diet or the basal diet containing 50, 75, 100, or 125 mg/kg Fe as SPCI diets. The experiment lasted for 21 d and on day 22, blood samples were collected 1 h later. The tissue and intestinal mucosa samples were collected following.ResultsOur results showed that the feed to gain ratio (F:G) decreased with different levels of SPCI addition (P< 0.05). The average daily gain (ADG) (P< 0.05) and digestibility of crude protein (P< 0.01) decreased with 125 mg/kg SPCI addition. With dietary different levels of SPCI addition, the serum concentrations of ferritin (quadratic,P< 0.001), transferrin (quadratic,P< 0.001), iron content in liver (quadratic,P< 0.05), gallbladder (quadratic,P< 0.01) and fecal (quadratic,P< 0.01) increased quadraticly. While the iron content in tibia (P< 0.01) increased by 100 mg/kg SPCI supplementation. Dietary 75 mg/kg SPCI addition increased the serum insulin-like growth factor I (IGF-I) (P< 0.01) and SPCI (75 ~ 100 mg/kg) addition also increased the serum content of IgA (P< 0.01). The serum concentrations of IgG (quadratic,P< 0.05) and IgM (quadratic,P< 0.01) increased quadraticly by different levels of SPCI supplementation. Moreover, different levels of SPCI supplementation decreased the serum concentration of D-lactic acid (P< 0.01). The serum glutathione peroxidase (GSH-Px) (P< 0.01) elevated but the malondialdehyde (MDA) (P< 0.05) decreased by 100 mg/kg SPCI addition. Interestingly, SPCI supplementation at 75 ~ 100 mg/kg improved the intestinal morphology and barrier function, as suggested by enhanced villus height (P< 0.01) and villus height/crypt depth (V/C) (P< 0.01) in duodenum, as well as jejunum epithelium tight-junction protein ZO-1 (P< 0.01). Moreover, SPCI supplementation at 75 ~ 100 mg/kg increased the activity of duodenal lactase (P< 0.01), jejunal sucrase (P< 0.01) and ileal maltase (P< 0.01). Importantly, the expression levels of divalent metal transporter-1(DMT1) decreased with different levels of SPCI addition (P< 0.01). In addition, dietary SPCI supplementation at 75 mg/kg elevated the expression levels of critical functional genes such as peptide transporter-1(PePT1) (P= 0.06) and zinc transporter 1 (ZnT1) (P< 0.01) in ileum. The expression levels of sodium/glucose co-transporter-1 (SGLT1) in ileum (quadratic,P< 0.05) increased quadraticly by different levels of SPCI addition and amino acid transporter-1 (CAT1) in jejunum(P< 0.05) also increased by 100 mg/kg SPCI addition.ConclusionsDietary SPCI supplementation at 75 ~ 100 mg/kg improved growth performance by elevated immunity and intestinal health.