Influence of limestone particle size on performance and egg quality in laying hens aged 24-36 weeks and 56-68 weeks

One hundred and twenty ISA Brown hens aged 24-36 weeks and 120 ISA Brown hens aged 56-68 weeks were used to study the influence of limestone particle size and the animal's age on laying performance and egg quality. Two diets were used: a diet containing calcium carbonate in fine limestone particles (diet LF with limestone particles <0.5 mm), and a diet containing calcium carbonate in coarse limestone particles (diet LC with 91% of particles larger than 0.8 mm and smaller than 2.0 mm). The experimental unit consisted of a group of 10 hens, thus each treatment was replicated six times per age group. Hen-day egg production was higher and egg weight lower in young hens than in old hens (P<0.001). In younger hens, hen-day egg production was 87.0 and 89.4% in birds fed LF and LC, respectively. Corresponding hen-day egg production values in older hens were 73.5 and 79.9%. Lower egg production in hens aged 56-68 weeks was compensated in part by higher egg weight which was 62 and 63 g in younger hens fed diets LF and LC, respectively, and 67 and 68 g in older hens fed diets LF and LC, respectively (P<0.001). In younger and older hens, feeding the LC diet increased shell weight by 0.2 and 0.2 g (P<0.001), shell thickness by 4 and 8 mu m (P<0.001), shell Ca content by 2 and 2 mg/g DM (P=0.003), albumen height by 0.2 and 0.3 mm (P=0.003), and Haugh units by 0.8 and 0.2 (P=0.014), respectively. No increase in the shell breaking strength was observed. It can be concluded that LC with a particle size of 0.8-2.0 mm should be considered rather than fine ground limestone when formulating diets for laying hens both in the early and the late phase of production. (C) 2010 Elsevier B.V. All rights reserved.