LAUSR

The objective of this study was to evaluate the effects of dietary Bacillus subtilis supplementation and calcium (Ca) levels on performance, eggshell quality, intestinal morphology, and relative calbindin-D28k (CALB1) mRNA level of laying hens in the late phase of production. An experiment employing a 2 × 3 factorial arrangement of 3 levels of Ca (3.5, 4.0, and 4.5%) and the absence or presence of B. subtilis was carried out with a total of 576 Hy-Line Brown laying hens aged 72 to 79 wk. Every group had 8 replicates of 12 birds each. The results showed that 4.0 and 4.5% Ca levels improved (P < 0.05) apparent retention and serum Ca content of aged laying hens. Compared with the 3.5% Ca level, the 4.0% Ca level in diets increased (P < 0.05) thickness, eggshell weight, shell ratio, and eggshell Ca content of aged laying hens. Moreover, breaking strength, thickness, eggshell weight, shell ratio, eggshell Ca content, apparent retention of Ca in g/day, apparent retention of Ca in percent, villus height, villus height/crypt depth, serum Ca level, and relative CALB1 mRNA level of aged laying hens were all increased (P < 0.05) by B. subtilis supplementation in diets. The supplemental B. subtilis decreased feed conversion ratio (P = 0.001) significantly. In addition, there was an interaction effect between increased Ca levels from 3.5 to 4.5% and B. subtilis supplementation on crypt depth in the duodenum (P < 0.05). In conclusion, we found that both the increase in dietary Ca level from 3.5 to 4.5% and B. subtilis supplementation could enhance intestinal Ca absorption and improve eggshell quality of laying hens in the late phase of production (72–79 wk of age). Dietary supplementation of B. subtilis accompanying the 4.0% Ca level was appropriate in enhancement of eggshell quality.