Effects of Yeast β-Glucan Supplementation on Calf Intestinal and Respiratory Health

The physiological functions of newborn calves are undeveloped, especially the immune system, making them susceptible to infections. In recent years, the theory of trained immunity has attracted attention and provided new strategies to prevent unknown infections in animals. This study investigated the effects of feeding yeast β-glucan on the intestinal and respiratory health of calves during the suckling period. Newborn Holstein calves (average birth weight: 36.18 ± 0.61 kg, mean ± SE) were randomly assigned to two groups: the PO (Per Os) group (<i>n</i> = 22) and the CON (Control) group (<i>n</i> = 22). Calves in the PO group were fed a yeast β-glucan solution (0.1 g/mL, 65 mg/kg body weight) at 3 and 6 days of age, respectively, while calves in the CON group received equal volumes of sterile saline orally at the same time. Blood and fecal samples were collected at 7 and 30 days of age, respectively. The results showed that (1) Compared to the CON group, being fed yeast β-glucan resulted in an inflammatory response after 24 h of the second administration, including increased gene expression of interleukin-6 (IL-6, <i>p</i> < 0.01), interleukin-1 beta (IL-1β, <i>p</i> < 0.01), and malonaldehyde (MDA, <i>p</i> < 0.001) content. Also, stimulation with β-glucan increased the concentrations of secreted immunoglobulin A (sIgA, <i>p</i> < 0.01) and defensins (<i>p</i> < 0.05) in the rectal feces. (2) Pre-stimulation with yeast β-glucan effectively reduced the incidence of diarrhea (<i>p</i> < 0.05) and bovine respiratory disease (BRD, <i>p</i> < 0.05) from day 31 to day 60. (3) At 30 days of age, the pre-stimulated calves had significantly lower serum DAO (<i>p</i> < 0.001) and MDA levels (<i>p</i> < 0.05), while they had higher levels of serum IL-6 (<i>p</i> < 0.01) and fecal slgA (<i>p</i> < 0.05) than calves in the CON group. (4) Pre-stimulation with yeast β-glucan altered the intestinal bacterial community; the Beta diversity results showed that the CON group and the PO group were clustered separately in the principal coordinate analysis (PCoA) graph. Obviously, the PO group sample points were more clustered. In conclusion, this study highlights the potential of yeast β-glucan-induced trained immunity to improve calf health during the suckling period. The findings offer new insights into the prevention of intestinal and respiratory infections in calves.