Almond shells as a sustainable alternative to commercial insoluble fibre sources in piglets: effects on performance and digestive health

Nutritional strategies have been evaluated to alleviate the negative effects of weaning, including the incorporation of dietary fibre (DF). Dietary fibre comprises soluble and insoluble fractions, both important for intestinal health. This study evaluated the effects of three insoluble fibre (IF) sources-coarse almond shells (AS), wheat bran (WB), and a commercial IF source (CIF)-included in high-NDF diets (12.0%) for weaned piglets, compared with a lower-NDF control diet (NC; 10.2%). All diets were isoenergetic (net energy: 2550 kcal/kg) and isonitrogenous (crude protein: 16.3%). Growth performance, dry matter digestibility, diarrhoea incidence, jejunal gene expression, and jejunal and colonic microbiota composition were assessed 14 days post-weaning. Neither growth performance nor digestibility was affected by treatment (P > 0.05). Piglets fed AS showed lower diarrhoea incidence than NC-fed piglets (0.67 vs 1.67 days; P < 0.05). Jejunal gene expression revealed higher expression of growth factors (EGF, IGF1) in AS-fed piglets than in WB-fed piglets (1.86 vs 0.63, 1.20 vs 0.86; P < 0.05). Dietary treatments also influenced intestinal microbiota composition (P < 0.05). In the jejunum, IF (WB, CIF and AS) inclusion reduced the abundance of Proteobacteria compared with NC (0.31, 0.37, 0.32 vs 7.23%; P < 0.05). At family level, WB increased Lactobacillaceae abundance relative to NC (89.24 vs 42.51%; P < 0.05), whereas CIF and AS showed intermediate values (59.67 and 57.88%). In the colon, microbial communities were affected by both IF inclusion and fibre physicochemical characteristics (P < 0.05). CIF-fed piglets exhibited higher Proteobacteria abundance (5.35%) and lower richness (P < 0.05), while AS (1.81%) produced microbial profiles similar to NC and WB (1.22 and 0.79%). Overall, almond shells, characterised by their high IF content and coarse particle size, reduced diarrhoea incidence, increased jejunal growth factor expression, and promoted a favourable intestinal microbial profile without affecting growth performance or digestibility. These findings support the use of almond shells as a sustainable alternative fibre source in piglet nutrition.