In this study, the effect of dietary supplementation of mulberry leaf
polysaccharides (MLPs) on the immune parameters-i.e., the immune organ weight, serum
immunoglobulins,
cytokines,
nitric oxide (NO) production, and
insulin-Like growth factor-1 (IGF1)
mRNA expression-of weanling pigs as a model animal was investigated. A total of 120 healthy weanling pigs (aged 28 ± 2 d) with the same
body weights were randomly divided into four groups: (1) Control treatment (CT), basal diet (BD), (2) MLP low-dose treatment (MLT), 0.6 g/kg MLP + BD, (3) MLP high-dose treatment (
MHT), 1.2 g/kg MLP + BD, and (4)
antibiotic treatment (AT), 0.15 g/kg
chlortetracycline + BD. The results revealed that the thymus and spleen indices were significantly increased (P < 0.05) in both MLT and
MHT groups in comparison with the CT group, while the serum levels of
immunoglobulin G (
IgG),
interleukin (IL)-1β,
IL-2,
IL-8, and
interferon (IFN-γ) in the MLT group and
IL-2,
IL-6, and IFN-γ in the
MHT group were also considerably greater (P < 0.05) than the corresponding levels in the CT group. The serum contents of
IgG, IL-1β,
IL-2, and
IL-8 in the MLT group and
IL-2 and
IL-6 in the
MHT group were significantly increased in comparison with the corresponding contents in the AT group (P < 0.05). The transformation rate of lymphocytes in the MLT and
MHT groups was higher compared to the CT and AT groups. However, a notable difference was found between the MLT group and the two control groups. The peripheral lymphocyte NO production in the MLT,
MHT, and AT groups was significant relative to the CT group. The expression levels of IGF1
mRNA in the liver and muscle longissimus tissues of both the MLT and
MHT groups showed significant improvement (P < 0.05) over those in the CT group. Moreover, the IGF1
mRNA expression in the muscle longissimus from the MLT group was significantly higher than in the AT group. In conclusion, the results suggest that incorporating MLPs into the diets of weanling pigs improves the animals' metabolisms and immune functions, and the effects of the MLT group were superior to those of both the
MHT and AT groups.