Effects of Lactobacillus paracasei LK01 on production performance, egg quality, antioxidant capacity, immunity and intestinal health of laying hens

This study aimed to evaluate the effects of dietary supplementation with <i>Lactobacillus paracasei</i> LK01 on production performance, egg quality, serum biochemical parameters, antioxidant capacity, inflammatory factors, intestinal digestive enzyme activities, and cecal microbiota in laying hens, while determining the optimal supplementation level. A total of 288 healthy 20-week-old Jinghong No. 1 laying hens, with uniform body weight and similar egg production rates, were stratified-randomly assigned to four groups (4 replicates/group, 18 hens/replicate): the control group (CON; basal diet) and the low-level (LLP), medium-level (MLP), and high-level (HLP) groups, which received the basal diet supplemented with 10⁶, 10⁷, and 10⁸ CFU/kg of <i>L. paracasei</i> LK01, respectively. The trial included a 1-week adaptation period followed by an 8-week experimental period. Results indicated: (1) <i>L. paracasei</i> LK01 supplementation increased average egg weight and significantly enhanced egg production rates in the MLP and HLP groups compared to the CON group (<i>p</i> < 0.05); (2) The HLP group exhibited increased albumen height and Haugh units, while the LLP group showed improved eggshell strength (<i>p</i> < 0.05); (3) Total protein (TP) levels were elevated in all supplemented groups (<i>p</i> < 0.05), with albumin (ALB) levels increased in the LLP and MLP groups, and total cholesterol (TC) and triglyceride (TG) levels decreased (<i>p</i> < 0.05); (4) Total antioxidant capacity (T-AOC) was enhanced in all supplemented groups, and serum IL-6 and TNF-<i>α</i> levels were reduced in the HLP group (<i>p</i> < 0.05); (5) No significant differences were observed in intestinal digestive enzyme activities (duodenum, jejunum, ileum) between groups (<i>p</i> > 0.05); At the phylum level, the abundance of <i>Spirochaetota</i> was decreased in all supplemented groups (<i>p</i> < 0.05), with <i>Bacteroidetes</i> and <i>Firmicutes</i> remaining the dominant phyla. At the genus level, the abundances of <i>Fusobacterium</i> and <i>Treponema</i> were reduced in all supplemented groups (<i>p</i> < 0.05). In conclusion, dietary <i>L. paracasei</i> LK01 improved laying hen performance, egg quality, serum biochemical parameters, antioxidant capacity, and reduced pro-inflammatory factors while suppressing harmful gut microbiota. The 10⁸ CFU/kg dose appeared optimal based on results; However, as this was the highest concentration tested, further research is needed to confirm the precise optimal level.