Di Blasio, S.; Middlekoop, A.; Molist, F.; Cord-Landwehr, S.; Elrayah, A. A.; Guardabassi, L.; Good, L.; Pelligand, L.

Managing post-weaning diarrhoea (PWD) in piglets is difficult due to limits on antibiotics and zinc. Chitosan is emerging as a potential feed additive. We analysed a chito-oligosaccharide hydrochloride (COS-HCl), a low molecular weight (LMW) chitosan, and a medium molecular weight (MMW) chitosan, and assessed their effects on growth, faecal consistency, microbiota, and potential interference with enterotoxigenic Escherichia coli (ETEC). The three chitosans were characterised using H-NMR, SEC RI MS, and SEC RI MALLS. COS HCl had an Mw of 0.824 kDa; LMW and MMW showed Mw ranges of 14.4 kDa (0.3-30 kDa) and 116 kDa (15-600 kDa). Degrees of acetylation were 9.5%, 6.5%, and 15%. Two 42-day field studies evaluated average daily gain (ADG), faecal consistency, and microbiota. In the first trial, COS HCl at 0.025_0.1% did not significantly affect ADG. In the second, LMW and MMW at 0.01% did not significantly change ADG. Faecal consistency, ETEC shedding, and microbiota composition were similar to controls. An enzymatic HPLC MS method enabled quantification of MMW chitosan in premix. Our results highlight the importance of advanced chitosan characterisation for precision nutrition and suggest that a threshold dosemay be needed to benefit growth and gut health in PWD management