Eggshell formation is a classical and rapid biomineralization process. In a span of less than 20 hours, about 2 grams of calcium deposits as calcium carbonate in the eggshell gland. As already mentioned, hens receiving B. velezensis DSM 15544 in their diet have a higher egg weight compared to hens receiving the same diet without the probiotic1,2,5. In practice, an increase in egg size is often negatively correlated with shell quality. With the probiotic, however, in all cases, larger eggs did not result in thinner eggshells or compromise the eggshell strength. In contrast, even thicker eggshells5 and fewer cracked eggs2 were noticed when egg size was increased.
Calcium absorption declines in older laying hens and can partly explain the reduced eggshell quality during the late production phase. Dietary probiotics can help to maintain eggshell quality and supplementation enables the egg producers to prolong the laying period. In aged laying hens, the addition of B. velezensis DSM 15544 resulted in higher shell weight, an increase in eggshell thickness and as a result, improved eggshell strength4,6. The eggshell breaking potential reduced from 3-4% in the control group to less than 1% in the Calsporin® treated group6.
Support nutrient and calcium absorption
Improved performance and eggshell quality can be explained by better feed utilisation by the hens, as it was shown that the apparent digestibility of protein, fibre and ash was significantly higher in 70-week old birds receiving B. velezensis DSM 155442. Recently, a new trial confirmed the improved apparent digestibility of calcium in 79-weeks old laying hens4. Increased absorptive area (higher villi and villi-crypt ratio)4,7 and transcellular transport by CALB1 (a major component of transcellular Ca transport in the duodenum and upper jejunum)4 could explain the higher calcium absorption by the use of Calsporin®. Composition of the microbiota could also have an influence on the solubility and absorption of calcium. By the stimulation of the lactic acid production of commensal lactobacilli6, probiotics have the ability to decrease the luminal pH, beneficial for the dissolution and uptake of calcium. Higher calcium absorption in laying hens was also confirmed by higher calcium levels in the serum and increased calcium in the eggshell content, without affecting calcium levels stored in the tibia (figure 3)4.