Evaluation of limestones varying in calcium solubility on egg production performance and total tract calcium retention in Lohman LSL Lite laying hens

Limestone is one of the primary sources of Ca in poultry diets because it is often readily available and inexpensive. The amount and availability of Ca in limestone can vary due to factors such as the origin of the rock, particle size, and solubility. It is believed that larger particles that solubilize at moderate or slow rates may be advantageous by limiting Ca-phytate interactions and increasing retention time of particles in the gastrointestinal tract, which would lead to better utilization of Ca by the bird. There were 5 limestones evaluated with 2 dietary Ca levels fed per limestone (2.65 and 3.80 %) to Lohmann LS Lite hens from 50 to 66 wk-of-age. The 5 limestones differed in geographical origin within the U. S., particle size, and solubility. Utilization of low Ca diets (2.65 %) resulted in impairments in egg production, egg mass, feed efficiency, egg specific gravity, and eggshell breaking strength. There were few differences among the 5 limestones evaluated, albeit limestone 2, which had the lowest solubility at 30 min (88 %) and lowest Ca content (36.7 %), was generally inferior to the other limestones in both the 2.65 % and 3.8 % Ca diets. The results of this study highlight the importance of the dietary Ca level for supporting optimal egg production and eggshell synthesis. Further, some indication of limestone characteristics that may result in impairments to performance are provided, which will assist nutritionists in selecting which limestone to use in their rations.