Epsilon Archive for Student Projects

Abstract

Sodium chloride, NaCl, has been shown to have a severe adverse effect on shell quality in birds when received in drinking water. This is a major problem due to an increase of breakage of eggs and great economic losses in commercial egg production. This review focuses on what has been written about the effect of NaCl on eggshell quality in the laying hen, with emphasis on the function of the enzyme carbonic anhydrase (CA) in shell formation. CA is important for the shell formation through the catalyzation of the reaction CO2 + H2O <--> HCO3- + H+ in the shell gland. HCO3- concentration in the shell gland has been shown to be coupled to the secretion of Ca2+ from the blood to the shell gland lumen and together they form CaCO3. Studies have shown that NaCl inhibits the activity of CA which causes a reduced concentration of HCO3- and Ca2+ in the shell gland, resulting in a reduction of the shell quality. The NaCl affects several shell quality measurements such as shell weight, shell breaking strength and shell thickness. The effect depends on the hens’ age and strain, and there are also individual differences. Older hens are more sensitive to saline drinking water than pullets and the strain Isa Brown is less sensitive than the cross between White Leghorn and New Hampshire. The exact effect of NaCl on the eggshell formation is yet not fully understood and further research is needed. The best remedy for hens receiving saline water is desalination of the water, but preventative treatments such as supplementing the diet or water with ascorbic acid or zinc has also proven beneficial for the shell quality.