Effects of Limestone Source on Egg Production and Egg Shell Quality in Laying Chickens

Abstract

Laying hens require adequate calcium for bone and eggshell formation as well as other physiological functions. Limestone, dicalcium phosphate, oyster shell, bone meal, meat and bone meal are important calcium sources used in formulating diets for laying hens. Of these, limestone is widely used in Kenya because it is readily available and inexpensive. The objectives of this study were: (i) to determine the physical and chemical characteristics of limestone from two sources in Kenya. (ii) to evaluate the effects of limestone source and level of dietary Ca on layer performance and eggshell quality(iii) to determine effect of time of lay on eggshell quality. Limestone was purchased from Athi River (AR) and Ukunda in Kenyan Coast (UKC). Particle size and solubility of the limestones were determined. The specific minerals content was determined according to the AOAC procedures of 2016. One hundred and 144 birds at 25 weeks of age were selected from a layer flock at the Poultry Unit, University of Nairobi and used in this study. The birds were allocated randomly to experimental cages. Six experimental diets, the first three based on UKC and the others on AR limestone were formulated. Each limestone source was included in the diet such that calcium level was 1%, 2% or 4% in a 2X 3 factorial design. A depletion diet containing less than 1% calcium was also formulated. The birds were fed on the experimental diets for a period of 60 days. Each diet was fed to a group of six birds and was replicated four times, giving 24 birds per treatment. Prior to this the birds had been placed on a depletion diet for about 10 days until production of thin shelled eggs was observed. Egg weight (g), hen-day egg production (%), egg breakage (%), feed intake (g/bird/day), feed conversion ratio (kg/dozen), specific gravity (g/cm3), shell weight (g), shell thickness (mm), shell percentage (%) and cost of feed (Kshs/kg or Kshs/dozen eggs) were determined. Data on time of lay was collected on the 1st, 4th and 7th week of lay at 9.00am, 12.00 noon and 3.00pm, respectively. Data analysis was done using GenStat Statistical package and significant treatment means separated using Tukey’s test.....................