From the vendor’ email to me:
We did testing on the clam and coral mixes that are out there. Chickens and ducks cannot absorb any calcium from them, they are very hard and just pass through their system.
I'd like to see the data not just a vendor's word.
Here's a study (in pdf form) regarding 5 different calcium sources including clam shells and oyster:
https://www.sciencedirect.com/scien...3323537393131393439373434372d6d61696e2e706466
Within it, the results:
"The mean body weights of the birds receiv-
ing the six supplemental calcium treatments
are presented in Table 3. There were no
significant treatment differences in body
weights at any age measured.
Mean feed efficiency, egg production and
livability are presented in Table 4. Although
numerically superior, the feed efficiency of
the birds receiving clam shell as the source
of supplemental calcium was not statistically
different from the mean feed efficiency of
the birds receiving the other supplemental
calcium sources. There were no statistically
significant differences among treatment
means for hen-housed egg production. The
hen-day production of the birds receiving the
diet adjusted for the protein content of the
egg shell meal or the limestone diet was
significantly greater than that of the birds
receiving the diet containing egg shell meal
but unadjusted for the protein in this supple-
mental calcium source. Differences between
other means for hen-day egg production were
not statistically significant."
