Nutritional factors are often suspected as a prime cause of shell-quality problems. If such problems occur, check the following list of nutrients which play an important role in shell quality:
Calcium
Calcium intake should be between 3.8 and 4.2 g per bird and per day, and be maintained by adjusting the diet formulation or by the use of calcium ‘icing’ (sprinkling large particles of a calcium source on top of feed in troughs), starting 2 weeks before lay.
Phosphorus
Total phosphorus intake should be below 0.8 g per bird and per day. The ratio of calcium to phosphorus should be as near 6:1 as practical.
Vitamin D3
Most custom-made premixes are adequate (2500–3500 IU/kg feed) in this vitamin, but high storage temperatures, long periods in storage and poor mixing may result in deficiencies. Products such as ROVIMIX® Hy•D® might be considered to complement the vitamin D3 supply of laying hens.
Magnesium
Problems can arise if intakes are greater than 0.7 g per bird and per day. Calcium sources that contain magnesium, particularly dolomitic limestones, can result in magnesium levels that are too high.
Chloride
An excess of chloride in hot weather may increase shell-quality problems. Dietary chloride should not exceed 0.25%.
Saline water
Relatively low levels of excess salts in drinking water can increase the incidence of cracked and broken eggs within one week of exposure. For example, the ability of the bird to produce normal egg shells is permanently affected by levels of sodium chloride from as low as 200 mg/L.
Note that the actual intake of the nutrient is important, not just the proportion of a nutrient in the diet. For example, if calcium is included in a diet at 4.0%, but the hen is consuming only 90 g of feed per day, its actual intake is 4.0/100 x 90 = 3.6 g of calcium per day. Intake can be affected by the energy level of the diet, the breed of hen, the stage of production, and the environmental temperature. (High shed temperatures can also decrease the efficiency with which the hen uses the nutrients she does consume.)
