In rural areas, springs, creeks and wells are often used as water sources for poultry farms.  Water coming from these sources, especially ground water, may be high in dissolved mineral salts, including sodium chloride.

Sodium chloride, NaCl, is essential for poultry, but it has been shown to have a severe adverse effect on shell quality when received in high concentrations through drinking water. NaCl reduces the breaking strength, shell thickness, shell weight, shell weight/egg weight and shell weight/unit surface, resulting in a higher incidence of cracked, broken and soft eggs. In breeders, saline water leads to a reduced numbers of settable eggs (eggs with an adequate shell quality for incubation) and to a lower hatchability.

Sensitivity to saline water

Sensitivity towards saline water depends on the age of the birds, breed, and individual factors of each hen or flock. Some animals are sensitive to concentrations as low as 200 mg NaCl/l drinking water, while others continue to lay good quality eggs at 2 g NaCl/litre.

When hens are exposed to saline water, the eggshell formation process is altered and, even if they are switched to water with less salinity or given any supplement for treatment, it takes at least 8 weeks to get back to normal.

With age, hens become more sensitive to saline water:

• It is possible to prevent the negative effects of NaCl in pullets that have been exposed to saline water before sexual maturity, by administering a preventive treatment as will be discussed later or switching to water with less salinity.
• Hens that are exposed to saline water at the beginning of the laying period often do not show shell defects until a much later stage, at 29 to 55 weeks of age (delayed effect). Even if after the administration of saline water they are switched to water with less salinity, the eggshell defects will appear anyway because the animals struggle to recover from the damage made by NaCl.
• Hens that receive saline water during the laying peak rapidly show a significant worsening of shell quality, but still can recover after 8 weeks or more if switched to water with less salt.
• Hens that are older than 40 weeks show a higher increase in the percentage of damaged eggs and can not fully recover from the damage produced by saline water.

Furthermore, different breeds of hens have different sensitivity to NaCl. In example, Isa Brown is more resistant than the cross between New Hampshire and White Leghorn. However, it must be taken in account that there is a lot of individual variation and one breed may show a high sensitivity in certain circumstances and be resistant in others.

Interference of NaCl with eggshell formation

The eggshell consists of 95% calcium carbonate, that is produced during eggshell formation from carbonate and calcium.