Background: Specific sources of dietary fibres in sow gestation and lactation diets, such as inulin or wheat bran, have been shown to affect both the sow and its litter health by modulating the piglet’s intestinal microbial population and composition. However, only a few studies have reported the effects of some specific fractions of the cell wall of the plants in the sow’s lactation diet. Therefore, this study investigates the effect of increasing the level of HCs in a sow’s lactation diet on the nutrient apparent total tract digestibility (ATTD), the faecal volatile fatty acid (VFA) profile, the microbiota of the sow and the microbiota and the performances of slow-growing (SG) and fast-growing (FG) piglets. Results: Increasing HCs level increased (P < 0.05) the proportions of butyrate and valerate on day 3, and the ATTD of acid detergent fibres (ADF), neutral detergent fibres (NDF), and gross energy and decreased (P < 0.05) the proportion of propionate on day 17, and the ATTD of crude protein. The beta diversity was affected (r2 = 0.11; P = 0.02) by the maternal dietary treatments with 11 common genera differing (P < 0.05) in the sow’s faecal microbiota, and five in the piglet’s microbiota. Regardless of the maternal dietary treatment, SG piglets had a lower (P < 0.05) proportion of isobutyrate and isovalerate, a lower (P < 0.05) abundance of Lachnospiraceae_XPB1014_group, Enterococcus, and Succinovibrio genera, and a greater (P < 0.05) abundance of Olsenella than FG piglets. Conclusions: Increased HCs level in a sow’s lactation diet affects the ATTD of nutrients, the faecal VFA and microbiota profiles of the sows with limited effects on SG and FG piglets’ faecal microbiota and no effects on the performance or VFA profile of these piglets.