Extended Abstract
Calcium is a critical factor for egg production, but little is known about the optimal way of providing this for laying hens. Limestone, the predominant Ca source in poultry feeds worldwide, can have particle sizes that are widely different which will impact the concentration of reactive (soluble) Ca, also, through chelation with phytate, can have a profound impact on the efficacy of phytase. This study was carried out to determine the effects of limestone particle size, and phytase enzyme supplementation production performance, egg quality traits, and coefficient of apparent digestibility of calcium in commercial laying hens.
Materials and Methods
All animal care procedures were approved by the Razi University Animal Care and Use Committee. A total of 216 laying hens of comparable BW at 18 wk of age was randomly distributed in six treatments, and six replicates per each. The design consisted of a factorial arrangement of three particle sizes of limestone from the same source (fine (<0.5 mm), medium (0.5-2 mm) and coarse (2-4 mm)) and two phytase levels (0 and 300 (FTU)/kg) in a completely randomized design. Productive performance was recorded during the experimental period. Egg samples were collected, and digestibility studies were conducted at week 6 of the experiment. Replicate (n = 6) was taken as the experimental unit, except where noted otherwise, 2 sampled birds per replicate were used. The effects of particle size and phytase enzyme were analyzed by the 2-way ANOVA procedure of SAS (SAS Institute Inc., 9.4.1, 2014) with P < 0.05 indicating significance.
Results
Results showed that egg production and egg mass were not influenced by experimental diets. Phytase inclusion numerically increased egg weight in second (P=0.06) and whole trial period (20-26 wk, P=0.1). Fine and coarse particles of limestone increased shell thickness (P < 0.01), compared to medium particles, also phytase supplementation improved shell percent (P < 0.01). Fine and medium sizes of limestone resulted in a higher apparent digestibility coefficient of Ca compared to coarse size ((P < 0.0001), 0.43, and 0.45 vs. 0.33). Diets containing medium limestone size showed lighter yolk color than those containing fine and coarse particles (P˂0.05). Medium size of limestone significantly increased digestibility of DM compared to fine and coarse particles.
Conclusion
In conclusion, productive performance of laying hens did not respond to limestone particle size, however, fine and medium sizes of limestone through enhancing effect on Ca digestibility, is more suitable than coarse particles for practical applications in young layers. Also, inclusion of phytase enzyme improved egg shell quality.
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