Grass hay mixed-in creep feed or separately-fed differentially affects digestive development in pre- and post-weaning piglets.

BACKGROUND: Based on observations in feral pigs, the role of dietary fibre and structure may be underestimated in suckling piglet nutrition. This study investigated the effect of grass hay offered to suckling piglets either separately or included in their creep feed, combined with nursery diets with or without grass pellet inclusion on growth performance and gastrointestinal development. METHODS: Thirty-six litters (14-15 piglets per litter) were divided into three equal groups of 12 litters per treatment during the suckling phase: control group (CON) received regular creep feed; GH group received chopped grass hay as-is in separate feeders alongside regular creep feed; PGH group received regular creep feed but barley and wheat were replaced by 28% grass pellets. After weaning (d 23), each litter was split into two dietary treatments in a split-plot design (pre-wean treatment as main plot). Two of the pre-wean diets were also offered until d 14 post-weaning, i.e., CON (CON nursery diet, CON-C, GH-C, PGH-C) and PGH (GH nursery diet, CON-GH, GH-GH, PGH-GH). Thereafter, transitioning to a diet containing 13% wheat/barley or grass pellets, respectively, until d 39 post-weaning. Gastrointestinal morphology, gene expression of intestinal nutrient transporters and barrier proteins, metabolite profile and microbiota were assessed on the day before weaning, d 10 and d 38 post-weaning. A total of 24 piglets were sacrificed at each dissection point. RESULTS: At weaning, GH group had consumed 7 g/piglet grass hay, and PGH group had consumed 46 g/piglet creep feed. One day before weaning, GH piglets showed heavier emptied small intestine (P = 0.044) and colon (P = 0.065), higher SCFA production in proximal segments and lower SCFA production in colon (P < 0.05). Higher abundance of Prevotellaceae NK3b31 group was observed in caecal and colonic content of PGH compared to GH group (P < 0.05), and PGH group showed a lower energy conversion ratio (net energy intake/gain, P = 0.035). Following weaning, GH nursery group had a reduced average daily gain (226 vs. 183 g, P < 0.001) during d 0-14, while this group showed compensatory growth afterwards (P = 0.056). Main plot effects on increased expressions of CLDN3 and FFAR2 were observed in GH and PGH by d 38 post-weaning (P < 0.05). An interaction effect showed greater luminal abundance of the Prevotellaceae NK3b31 group in GH-GH and PGH-GH groups compared to CON-GH on d 38. The GH nursery diet showed a better energy conversion ratio (P = 0.006) with no influence on body weight and their SCFA production shifted towards proximal segments. CONCLUSION: In conclusion, feeding a structured and fibre-rich diet to suckling piglets enhance their digestive tract development and adapt their microbiome to fibre digestion in later life. Maintaining a fibre-rich diet from suckling to nursery is recommended, though this come with a transient reduction in weight gain caused by lower feed intake that, however, can be recovered afterwards accompanied with an optimized energy conversion ratio.