Dietary tea tree oil supplementation improves the intestinal mucosal immunity of weanling piglets

Abstract

Tea tree oil (TTO) is a kind of plant extract with anti-inflammation and anti-tumor functions. However, little is known about the effects of TTO on intestinal mucosal immunity. In the present study, ninety 21-day-old weanling piglets (6.73 ± 0.12 kg) were randomly divided into 5 treatments, which were the control (CON, feed with basal diets), the antibiotics supplemented treatment (ANT, feed with antibiotics-supplemented diets), and the low-, middle- and high-level TTO-supplemented treatments (LTO, MTO and HTO, feed with 50 mg/kg, 100 mg/kg and 150 mg/kg TTO added diets, respectively). After 21 days of the experiment, TTO supplementation increased the average daily feed intake (ADFI) (P < 0.05) and showed a trend of increased average daily gain (ADG) (0.05<P < 0.1) of the weaned piglets. The villus length of the jejunum (P < 0.001) and the ratio of the villus length versus the crypt depth (V/C) of all of three segments of the small intestine (SI) (P < 0.01) were improved by the TTO treatments. TTO supplementation also increased or led to a trend of increased contents of interleukin(IL)-2 in the jejunum (P < 0.05) and in the ileum (0.05<P < 0.1), IL10 in the jejunum (0.05<P < 0.1) and interferon-γ (IFN-γ) in the ileum (0.05<P < 0.1). The gene expression of IL1β (P < 0.01) and IL10 (P < 0.01) in the jejunum, tumor necrosis factor-α (TNFα) (P < 0.05) in the ileum and occludin in the ileum (P < 0.01) were all upregulated under the TTO treatments. TTO supplementation increased the gene expression of heat shock protein (Hsp)60 (P < 0.05), Hsp70 (P < 0.01) and Hsp90 (P < 0.001) in the jejunum and upregulated the gene expression of Hsp70 (P < 0.05) and Hsp90 (P < 0.01) in the ileum. In addition, TTO supplementation activated Notch2 signaling in the SI (P < 0.05). ANT supplementation could also improve intestinal development, increase cytokines secretion, upregulate the gene expression of tight junction proteins and activate the gene expression of Notch2 signaling of the SI to some extent. However, TTO exhibited better effects. In conclusion, TTO supplementation could improve the intestinal mucosal immunity of weaning piglets, and the effects were better than those of the antibiotics; this outcome was probably associated with the activation of Notch2 signaling.