Maternal Daidzein Supplementation during Lactation Promotes Growth Performance, Immunity, and Intestinal Health in Neonatal Rabbits

The main purpose of the present research was to evaluate the effect of varying levels of DA inclusion in maternal diet, in the form of powder, on the born-weaning growth performance (days 1–30) and intestinal health of neonatal rabbits. A total of 152 delivered maternal does (3.94 ± 0.05 kg) were allocated into four groups, with thirty-eight replicates of one doe each, and fed with a control diet (CON) supplemented with different levels of powdered DA (85 mg/kg (DA85), 170 mg/kg (DA170), and 340 mg/kg (DA340)) during lactation. The results show that dietary DA increased individual body weight at days 21 and 30 ( p = 0.03 and p < 0.01) and showed a linear and quadratic effect on individual body weight and average daily gain (ADG) ( p < 0.05), although ADG was not affected by DA. The serum progesterone (P) ( p = 0.05) and glutathione peroxidase (GSH-Px) ( p = 0.01) concentrations of maternal rabbits were increased in all maternal DA-supplemented groups and showed a linear and quadratic effect ( p < 0.05), while a linear effect was observed in estrogen (E-2) ( p < 0.05). Interestingly, the concentrations of the serum insulin-like growth factor-1 (IGF-I) ( p < 0.01) and immunoglobulin (IgA and IgG) ( p < 0.01 and p = 0.01) in neonatal rabbits were increased in all dietary DA groups, and both showed a linear and quadratic effect ( p < 0.05). In addition, the serum interleukin (IL-1β) ( p = 0.03) and catalase (CAT) ( p = 0.04) concentrations were affected by DA supplements, but linear and quadratic effects were only observed in the catalase (CAT) of neonatal rabbits ( p < 0.05). Importantly, the duodenal and jejunal villus heights ( p < 0.04 and p = 0.01) and the ratio of villus height to crypt depth ( p = 0.02 and p = 0.01) in neonatal rabbits were elevated in all DA-supplemented treatments, while a linear and quadratic effect was observed in jejunum, but a quadratic effect was observed in duodenum ( p < 0.05). The ileal villus height ( p < 0.01) was also elevated in all DA-supplemented treatments exhibiting both linear and quadratic effects ( p < 0.05). Moreover, the expression levels of occludin ( p = 0.04), zonula occludens-1 (ZO-1) ( p < 0.01), IGF-1 ( p = 0.03), and solute carrier family 5 member 9 (SCL5A9) ( p < 0.01) in jejunum were markedly elevated in the DA175 and 340 mg/kg DA-supplemented groups and were showing linear and quadratic effects ( p < 0.05). Finally, inflammation-related gene expression levels such as NF-κB, TLR4, and MYD88 in jejunal ( p = 0.01, p = 0.04, and p < 0.01) and ileal ( p = 0.04, p = 0.04, and p = 0.03) epithelium were decreased in the DA170 and DA340 groups ( p < 0.05), while linear and quadratic effects were observed for TLR4 in jejunum and for NF-κB and TLR4 MYD88 in ileum ( p < 0.05). In summary, as a functional additive, maternal DA supplementation with 170 and 340 mg/kg DA during lactation can promote the growth of neonatal rabbits, which is related to improved antioxidative capacity and immunity, as well as improved intestinal health in neonatal rabbits.