| Four experiments were conducted to investigate the preparation of β-glucan and its effects on growth performance and immune function in weaned pigs. 1) Preparation of B-glucan using Saccharomyces cerevisiae. The results showed that B-glucan was offwhite, flavourless, and insoluble in water with 5.49% of crude protein and 89.7% of polysaccharide. Its structure was the typical structure of B-glucan extracted from Saccharomyces cerevisiae. The main component of monosaccharide of the prepared B-glucan was glucose. 2) One hundred weaned pigs (8.65 ± 0.42 kg and 28 ± 2 d of age) were used in a 35-d experiment to determine the effects of graded levels of B-glucan. Pigs were randomly allotted to one of five treatments containing B-glucan supplemented at 0, 25, 50, 100, and 200 ppm. Each treatment was replicated using five pens containing four pigs per pen. The ADG of pigs between days 14-28 and days 0-28 responded to dietary B-glucan in a quadratic fashion (P < 0.05), while B-glucan had no effects on ADFI and G:F in each period, which indicated that the optimal dose used in the diets of weaned pigs is 50 ppm. 3) Eighty crossbred pigs (8.23 ± 0.56 kg and 28 ± 2 d of age) were used in a 35-d experiment to investigate the effects of B-glucan on performance and lymphocyte proliferation in different sex of weaned pigs. Pigs were allotted to one of two dietary treatments (0 or 50 ppm fl-glucan in the diet) using ten pens with four pigs per pen. Pigs treated with B-glucan had higher ADG in the 14-28 d (P = 0.05) and 0-28 d (p< 0.05) periods. ADFI of pigs in the treatment group was increased (P < 0.05) in the 0-14 d, 0-28 d and 28-35 d periods. Lymphocyte proliferation index response to phytohemaggiutinin (P - 0.051) and concanavalin A (P = 0.052) tended to decrease on d 14 in pigs supplemented with B-glucan compared with pigs without supplementation. No differences in performance and lymphocyte proliferation in response to B-glucan addition were detected between different sex pigs in each period. 4) Twenty-four barrows were used to investigate the effects of β-glucan on immune function and samototropic axis in weaned piglets. Pigs (8.89 ± 0.20 kg and 28 d of age) were raised individually and randomly divided into two groups. Pigs in each group were fed a diet supplemented with either 0 or 50 ppm P-glucan. All pigs were injected with ovalbumin (OVA) on d 14 to investigate their humoral immune response. On d 28, lymphocytes were isolated from all pigs to determine the effects of B-glucan on cellular immunity of pigs in vitro. Lymphocytes from half of the pigs in each group (n = 6), were incubated with lipopolysaccharide (LPS), the remainder with an equivalent volume of culture medium alone. Samples were collected at 0, 3, 6, 12, 18, 24, and 48 h after LPS addition for determination of interleukin-6 (IL-6), tumor necrosis factor-a (TNF-α). and interleukin-10 (IL-10). On d 31, half of the pigs (n = 6) in each group were also injected with either LPS (25 μg/kg body weight) or an equivalent amount of sterile saline. Blood samples were collected at 3 h after LPS injection for analysis of IL-6, TNF-α, IL-10, insulin-like growth factor-I(IGF-I), cortisol, and growth hormone (GH) in plasma. The results indicated that dietary p-glucan enhanced pig antibody response to OVA the first week after injection, but this effect did not persist to the second week. In vitro, the increases of IL-6 and TNF-α in culture medium were partially dampened in pigs supplemented with B-glucan when their lymphocytes were incubated with LPS, whereas the increase of IL-10 was potentiated. In vivo, dietary B-glucan attenuated the increase of plasma IL-6 and TNF-α, and enhanced the increase of plasma IL-10 when pigs were challenged with LPS. Additionally, the decrease of the concentration of IGF- I was alleviated in pigs supplemented with B-glucan, whereas no differences were detected in cortisol and GH between treatments. These results demonstrate that B-glucan can enhance the humoral immune function, modulate cellular immunity, and improve the performance in...
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