Specific fractions of dietary fibres (DFs), such as hemicelluloses (HCs), can affect the gut microbiota of lactating sows. In a recent study, we showed that a decreasing level of HC during lactation affected sow’s faecal microbiota, increased the proportion of acetate and propionate and decreased the proportion of butyrate and valerate in faeces. We hypothesise that those changes can in turn affect the faecal microbiota of the offspring. As slow growing (SG) piglets are more prone to diseases and show greater mortality than their fast growing (FG) siblings, the aim of the study was to test whether decreasing the level of HC in sow’s lactation diet differently affect the faecal microbiota and VFA profile of SG and FG piglets. From 110 days of gestation to weaning (25±0.4 day post-farrowing), 35 sows were assigned to one of four diets, formulated to contain either 13, 11, 9 or 8% of HC, the same level of DFs, to differ in the DF sources and to be isonitrogenous and isocaloric. Piglets were weighed at birth and at 16 days of lactation. According to their average daily gain (ADG), two piglets per litter were selected and divided in two categories: SG (n=35; 167±10.1 g/day) and FG (n=35; 280±10.1 g/day). Faeces were collected at 16 days of lactation. Results showed no interactions between the maternal diet and the growth rate. Regardless of the growth rate, 11, 9 and 8% of HC showed three genera that significantly differed (P adjusted<0.05) compared with 13% of HC: Faecalibacterium, Parasutterella and Dialister. Regardless of the maternal diet, FG piglets had a greater proportion of isobutyrate and isovalerate (P<0.01) in faeces compared to SG piglets. At the genus level, Enterococcus and Succinovibrio were more abundant (P adjusted<0.01) and Olsenella was less abundant (Padjusted <0.01) in FG than SG piglets. In conclusion, the present study confirmed an effect of the maternal diet on the microbiota of the progeny. Further studies are needed to better understand the association between the differences in ADG within the litter during the pre-weaning period and the faecal microbial composition
