In ovo injection dosage of Lactobacillus rhamnosus on intestinal health and microbial composition of yellow broilers with or without Eimeria challenge

Probiotic bacteria could be administrated to broilers using the in ovo injection technique during 17.50 and 19.20 d of incubation to accelerate microbial maturation in the intestinal tract. The effects of Lactobacillus rhamnosus (LR) injected in-ovo on intestinal morphology, mRNA expressions of intestinal health-related genes, and selected intestinal microbial of yellow broilers with or without Eimeria challenge were studied. A total of 360 yellow broiler hatching eggs were randomly assigned into 6 treatments with 60 replicate eggs per treatment. Six treatments were arranged in a 3 (LR dosage at 0, 10⁶, and 10⁸ CFU/egg at 18.5 d of incubation) × 2 (Eimeria oocyst challenge vs. PBS challenge at 10 d of age) factorial design. Tissues and cecal contents were sampled on d 19 posthatch. Our results indicated that the coccidial infection increased duodenum, jejunum, and liver relative weights to body weight, duodenal crypt depth, and HSP90 expression, and reduced goblet cell density and Occludin expression. In ovo injection of LR at 10⁶ CFU/egg downregulated the Occludin expression and increased the Clostridium perfringens level in Eimeria-challenged broilers. When the LR dosage increased to 10⁸ CFU/egg, relative weights of duodenum, jejunum, ileum, and liver increased, villus length of lower small intestine and cecal Lactobacillus abundance in challenged broilers were reduced, and the Escherichia coli and Clostridium perfringens abundances in unchallenged broilers were increased. In summary, in ovo injection of LR at a dosage equal to or higher than 10⁶ CFU per egg exacerbated coccidial infection in the intestinal tract and resulted in cecal bacterial imbalance. The probiotic dosage must be considered for in ovo administration in broiler production.