Effect Of Bacillus Licheniformis On Laying Performance Of Hens And Its Mechanism

Bacillus licheniformis have been widely used as probiotics due to their ability to improve intestinal health, enhance the immunity function of the host and exhibit a growth-enhancing effect. Currently, Bacillus licheniformis have been developed into various forms of feed-grade probiotics used in animal production. However, less is known about the effect of Bacillus licheniformis on performance of laying hens. A commercial probiotic strain Bacillus licheniformis was evaluated for its ability to modulate performance and egg quality, and explore mechanisms on Hy-Line Variety hens in this experimentFeeding trail:A total of 540 Hy-Line Variety W-36 hens (no significant deviation in body weight),28 wk of age, were randomly divided into six groups, each of which had 6 replicates of 15 hens. Three hens were housed per cage under the same management conditions in a windowed poultry house. Group 1 was fed with basal diet,and Groups 2-6 was fed with different concentrations (0.01%,0.02%,0.03%, 0.06% and 0.09%) of 2×1010CFU/g Bacillus licheniformis preparation. This trial lasted from 28 to 38 wk of age, including a 2 wk acclimatization period and 8 wk experimental period. Hen-day egg production, feed consumption, egg weight and hen mortality were recorded daily. Feed conversion ratio was calculated as grams of feed intake per gram of egg mass. At 38 wk of age,12 eggs from each replicate were randomly collected to assess egg quality parameters. Albumen height,Haugh units, yolk color, egGSH-Pxell thickness and egGSH-Pxell strength were measured with a digital egg tester after eggs were weighed and cracked open. At the end of the trail,12 hens (2 birds per replicate) were randomly selected to slaughter, and mucosa of jejunum and contents of gizzard, small intestine and cecum were collected for further analysis.Part I:The results clearly showed that all treatment groups had higher egg production and egg mass output compared with the control through a 56-d trial period(P< 0.05). Hens receiving B. licheniformis at 0.01% and 0.06% had improved egg production over hens fed the basal diet devoid of Bacillus. There is a trend of improving the egg weight in the experimental groups, but differences among treatments for egg weight were not observed (P> 0.05). There were also no significant differences for feed consumption and feed-conversion efficiency among all six groups(P> 0.05). The thickness and strength of egg shell were significantly increased in all B. licheniformis treated groups compared with the control(P< 0.05). There is a trend of improving albumen height and Haugh unit in the experimental groups, and Albumen height was significantly increased in 0.03% and 0.06% B.licheniformis group(P< 0.05), while Haugh unit significantly increased only in the 0.06% group(P< 0.05). Compared to the control, yolk color in 0.03% B. licheniformis group became darker (P<0.05), that in 0.09% B. licheniformis group lighter (P<0.05), and there was not significant change for other groups.Part Ⅱ:The results showed that B. licheniformis supplementation in the diet significantly decreased the activity of D-lactate and diamine oxidase(P< 0.05), which indicated that intestinal mucosal function has been improved significantly. Specific features as follow:(1) improve the mRNA expression of MUC-2; (2) The structure of intestinal villi has significalntly improved. Addition of 0.01% and 0.03% B. licheniformis significantly decreased the crypt depth(P< 0.05),while. the crypt depth of 0.06% B. licheniformis group was significant increased(P<0.05), and B. licheniformis treated groups showed better intestinal integrity. (3) The expression of tight junction of intestinal mucosal has evidently increased. The expression of cldn-1 and cldn2 was highest in Ⅳ (0.03%), and was significant compared with the control group (P<0.05). While, The expression of ZO-1 and OCLN-lwas highest in V (0.06%), and was significant compared with the control group (P<0.05). (4)The immune function of intestinal was also enhanced. Anti-inflammatory cytokine IL-4 accompanied by a significant increased villus height in jejumun(P< 0.05). Supplemented with of B. licheniformis could increased the level of SST and reduce the level of IL-6 in the jejunum (P>0.05). Compared with the control group, the composition ratio of flora in the cecum of II (0.01%) group did change little, and the firmicutes also take the advantage portion in the control group and II (0.01%) group. However, the aboundance of bacteroidetes in IV (0.03%) group and V (0.06%) group becomes the dominant bacteria, consisting of 50.2% and 49.5%, respectively.Part III:Compared with the control, B. licheniformis supplementation in the diet significantly decreased the level of ACTH and increased the level of E2 and FSH (P<0.05), while had no effect on CORH and LH(P>0.05). Supplementation with B. licheniformis could notably enhance the mRNA expression of GnRHand lower the mRNA expression of ghrelin and INH in ovary (P<<0.05). Compared to the control group, the mRNA expression of FSHR inV (0.06%) group (P<0.05), ESR-βin IV (0.03%) group (P<0.05), and ESR-αinⅡ (0.01%) group (P<0.05) was significantly decreased.Part IV:Addition of B. licheniformis in the diet showed less effect on the normal metabolism of hens, with the similar levels of ammonia, uric acid and alkaline phosphatase compared to the control(P> 0.05). Supplementation with 0.03% and 0.06% B. licheniformis increased GST activity (P< 0.05), and there were no differences for other antioxidant enzymes activities among all groups (P>0.05). The levels of IL-1 and IL-6 were significantly decreased in 0.01,0.03 and 0.06% B. licheniformis group(P< 0.05), and supplementation with 0.01% B. licheniformis also significantly decreased the levels of TNF-α (P<0.05). Supplementation with 0.01,0.03 and 0.06% B. licheniformis also significantly improved the levels of IL-4(P< 0.05). The addition of 0.03% B. licheniformis to the diet resulted in significantly increasing the levels of IgG(P< 0.05). There was no significant difference for IgA,IL-4 and IL-10 between the chickens fed on the basal diet and those receiving three different levels of B. licheniformis diets(P> 0.05).In conclusion, dietary supplementation of Bacillus licheniformis could improving performance of laying hens by increasing intestinal barrier and regulating secretion of some Reproductive hormones.