Abstract: The aim of this study was to investigate the effects of Enterococcus faecium (EF) and Bacillus subtilis (BS) supplementation on growth performance, serum biochemistry, and intestinal health of brood-rearing laying hens, as well as the carryover effects of feeding during this period on the subsequent laying performance. A total of 528 1-day-old Roman pink laying hens were selected in a 2×2 experimental design. BS consisted of two supplemental amounts of 0 or 200 mg·kg^-1 (BS viable count:3×10¹⁰ CFU·g^-1). EF consisted of two additions of 0 or 200 mg·kg^-1 (EF viable count:2×10⁹ CFU·g^-1). This experiment included treatments with six replicates per treatment and 22 hens per replicate. The experimental period lasted 30 weeks. The experimental treatment was carried out at brood-rearing period from 1 to 20 weeks. The laying period was from 21 weeks to 30 weeks and fed with basal diet. The results showed that:1) There was a significant interaction between BS and EF on the feed to meat ratio (F/G) of laying hens from 1 to 20 weeks, indicating that the combination of the two probiotics increased F/G ratio (P<0.05). 2) BS supplementation tended to decrease serum ALT level at week 20 (P=0.067). There was an interaction effect of BS and EF on serum biochemistry of laying hens at 20 wk, as indicated by the reduction of serum total protein, serum high-density lipoprotein and total cholesterol content by the combination of the two bacteria (P<0.05). 3) EF supplementation tended to increase serum GH level at week 20 (P=0.078). 4) BS and EF increased the relative length of ileum (P<0.05). The addition of BS tended to increase the height of jejunal villus (P=0.051) and crypt depth (P=0.069). EF supplementation significantly increased jejunal villus height (P<0.05), and tended to increase the depth of jejunal crypt (P=0.072). 5) BS significantly increased the relative expression of Occludin mRNA in the jejunal mucosa (P<0.05), and had a tendency to increase the relative expression of Claudin-1 mRNA (P=0.081). 6) Adding BS tended to increase the average egg weight (P=0.077). In conclusion, supplementation of BS can enhance the growth performance, serum biochemical indexes and intestinal health of laying hens during the brooding period. Furthermore, supplementing with BS during this period can also improve their performance during the laying period, surpassing that of EF and a combination of two probiotics.

Key words: hens, Bacillus subtilis, Enterococcus faecium, growth performance, serum biochemistry, intestinal health