Abstract: This study employed a single-factor experimental design to systematically evaluate the effects of dietary supplementation with varying levels of fermented mulberry leaves on growth performance, diarrhoea incidence, and intestinal microecology in weaned piglets. The objective was to provide a theoretical foundation for the scientific application of fermented mulberry leaves in piglet production. A total of 200 healthy DLY weaned piglets with similar initial body weight (8.52±0.63 kg) and age (28 days) were randomly allocated into five groups, each consisting of four replicates with 10 piglets per replicate. The control group received a basal diet, while the experimental groups were fed diets supplemented with 5%, 10%, 15%, or 20% fermented mulberry leaves, which had been prepared through co-fermentation with lactic acid bacteria and cellulase for 60 days. The experiment lasted for 28 days. Parameters measured included growth performance, diarrhoea rate, intestinal chyme pH, caecal short-chain fatty acid (SCFA) concentrations, and the populations of major bacteria in the jejunum and caecum. Over the entire experimental period (from 28 to 56 days of age), no significant differences were observed in average daily feed intake, average daily gain, or feed-to-gain ratio between the experimental groups and the control group (P＞0.05). However, during the period from 42 to 56 days of age, the 20% supplementation group exhibited a 14.78% increase in average daily gain compared with the control group, although this difference was not statistically significant (P＞0.05). Between 28 and 42 days of age, diarrhoea rates in all experimental groups were significantly lower than those in the control group (P＜0.05), with the 15% supplementation group showing the lowest rate (0.29% ), representing a 52.46% reduction relative to the control group (0.61% ). Over the full experimental period, the diarrhoea rate in the 15% supplementation group remained significantly lower—by 41.86%—than that of the control group (P＜0.05). Duodenal chyme pH values were significantly lower in all experimental groups compared with the control group (P＜0.05), and pH values in the jejunum, ileum, caecum, and colon followed a decreasing trend. Concentrations of acetic acid and propionic acid in the 10%, 15% , and 20% supplementation groups were significantly higher than those in the control group (P＜0.05). The 15% supplementation group recorded the highest acetic acid level (34.38 mmol/L), which was 47.05% greater than that of the control group (24.61 mmol/L). Supplementation with fermented mulberry leaves had no significant effect on the counts of Escherichia coli, Lactobacillus, or Bifidobacterium in the jejunal and caecal contents (P＞0.05). Nonetheless, the populations of Lactobacillus and Bifidobacterium in all experimental groups were generally higher than those in the control group. Under the conditions of this experiment, dietary inclusion of 5%～20% fermented mulberry leaves did not significantly enhance growth performance in weaned piglets but did markedly reduce diarrhoea incidence. Furthermore, it optimised the intestinal microecological environment by lowering pH in the proximal intestine and increasing the production of beneficial SCFAs(acetic acid and propionic acid) in the caecum. Overall, supplementation at the 15% level appeared most effective in alleviating diarrhoea and promoting intestinal health.

Key words: fermented mulberry leaves, weaned piglets, growth performance, diarrhea, intestinal microecology