Evaluation of aragonite as a calcium source in laying hen diets

     

Experiments were conducted to determine the bioavailability of fine ground aragonite (FGA) using 0-14 d old broilers and to determine the use of FGA on performance, eggshell quality, and tibia ash (TA) of laying hens from 28-56 wks. In experiment 1, 450 as hatched Ross 708 broilers were fed a basal diet without either LS or FGA containing 0.35% Ca and LS and FGA additions resulting in 0.43, 0.51, 0.59, and 0.67% Ca. Body weight gain, feed intake (FI) and feed efficiency (FE) were measured 0 to 14 d after which all remaining chicks were euthanized for TA. Slope ratio analysis was conducted and the relative bioavailability of FGA to LS using TA was 179%. In experiment 2, 180 Hy-Line W-36 laying hens were fed diets containing LS or FGA at 2.46, 3.28, or 4.10% Ca, corresponding to 60, 80 and 100% of breeder recommendations from 28-56 wks. The experiment was set up as a 2 x 3 factorial with Ca source and concentration, resulting in 6 treatments of 10 cages of 3 laying hens. Hen-day egg production (HDEP), egg weight (EW), egg mass (EM), FI, and FE were calculated over two wk periods. Body weights were measured and eggs collected every four wks to determine shell thickness, relative weight, breaking force, and egg specific gravity. Data were analyzed as a factorial with repeated measures in SAS (P ≤ 0.05) and means were separated using Tukey’s HSD test and TA was analyzed in JMP Pro 16.0 (P ≤ 0.10). Interactions occurred for HDEP, EW, EM, and FE between Ca concentration and source. In general, 100% LS resulted in the lowest performance among the treatments. Hens fed 100% LS (568 g/kg) had the lowest FE compared to 80 and 100% FGA (583 and 584 g/kg; P ≤ 0.01), with other treatments being intermediate. There was an interaction between Ca concentration and source for TA where all FGA treatments maximized TA, however, TA increased in a dose dependent manner for LS (P = 0.07) suggesting that the lower concentrations of limestone were insufficient to maintain egg production and TA over time. Limestone increased shell quality for all parameters measured (P ≤ 0.05). These data indicate that FGA may be used as a higher available alternative Ca source in laying hens based on performance, but more understanding of how FGA is used for eggshell formation is needed.

Key Words: limestone, aragonite, bioavailability, laying hen.