Tryptophan supplementation in low-protein diets of sows during late gestation and lactation: Effects on sow performance and piglet growth.

This study aimd to investigate the effects of tryptophan (Trp) supplementation in low-protein diets on sow performance and piglet growth, and its potential mechanisms. Sixty-six multiparous sows (Large White × Landrace) with similar parity (2.87 ± 0.34 parities), body weight (250.75 ± 11.24 kg), and backfat thickness (16.06 ± 1.94 mm) were randomly assigned to six groups. There were eleven sows in each group and one replicate per sow. They were fed the following diets: normal protein diets (18% crude protein [CP], control group [CON]) or low-protein diets (15% CP) containing different levels of Trp (0.15%, 0.21%, 0.27%, 0.33%, and 0.39%, respectively). The results showed that low-protein diets containing 0.21% Trp achieved performance comparable to the CON group. Specifically, no significant differences were observed between the 0.21% Trp group and the CON group in sow average daily feed intake, milk yield from 3 to 21 d, and piglet growth parameters (litter weight and individual weight at 3, 14, and 21 d, as well as average daily gain (ADG) from 3 to 21 d (P > 0.05). Furthermore, compared with the CON group, the 0.21% Trp group significantly increased the levels of fat-free dry matter and immunoglobulin A (IgA) in colostrum, reduced milk urea nitrogen (MUN), elevated serum total glutathione (T-GSH) in sows, and increased serum immunoglobulin G (IgG) in piglets (P < 0.05). Additionally, compared with the CON group, the 0.21% Trp group promoted intestinal health in piglets, as evidenced by increased ileal villus height, upregulation of intestinal physical barrier-related genes (occludin and claudin-1) in the jejunum and ileum, downregulation of pro-inflammatory cytokines (IL-6 and IFN-γ), upregulation of antioxidant genes (GSH-PX and CAT), as well as an increase in the abundance of the beneficial gut microbiota Christensenellaceae _R-7_group (P < 0.05). The experiment lasted from 107 d of gestation to 21 d of lactation. Data of this study suggested that low-protein diets containing 0.21% Trp improved sow performance and piglet growth to levels comparable to normal protein diets, probably due to the higher feed intake and milk yield of sows, the improvements in intestinal function and gut microbiota of piglets, and the higher antioxidant capacity of sows and piglets.