Limestone particle size in layer diets

[摘要] English: A specific calcitic limestone source that is widely used in South African poultry diets wasevaluated during two concurrent studies. During the first study, the effect of limestone particlesize on bone quality, egg production and eggshell quality was determined. Limestone wasclassified according to particle sizes as small (0-1.0 mm), medium (1.0-2.0 mm) and large (2.0-3.8 mm).During the second study, the effect of different distribution ratios of small and large particlesizes of limestone on bone quality, egg production and eggshell quality characteristics wasdetermined. Small (0-1.0 mm) and large (2.0-3.8 mm) particles limestone from the first studywere mixed to obtain the following five distribution ratios used in the second study namely; 0,25, 50, 75, 100% small or large particles.The experimental protocol for both studies was the same. Initially one hundred and thirty eight,17 weeks old Lohmann-Silver pullets, were obtained from a commercial egg producer andrandomly allocated to six treatments (n=23/treatment). All birds were kept in individualmetabolic cages for the duration of the study. The influence of limestone particle size anddistribution ratios of particles on feed intake, body weight and egg production was determinedfor weeks 33 up to week 70 of age. During weeks 54, 58, 62 and 70 of age, the effect oflimestone particle size and distribution ratios of particles on eggshell quality characteristics suchas shell weight, percentage eggshell, eggshell calcium egg surface area, shell weight per unitsurface area (SWUSA) and shell thickness was determined. At 70 weeks of age, the effect oflimestone particle size and distribution ratios of limestone particles on bone dimensions (length,width and weight), bone mechanical properties (breaking strength and stress) and percentagebone ash was determined.The results of the limestone particle size study indicated that different limestone particle sizesdid not have a significant influence on feed intake (P=0.6229), body weight (P=0.4189), eggproduction (P=0.3991), egg output (P=0.0599) and feed conversion ratio (P=0.5025).Accordingly different limestone particle sizes did not show any significant effect on meaneggshell characteristics such as shell weight (P=0.9396), percentage eggshell (P=0.3468),eggshell calcium (P=0.9367), egg surface area (P=0.3223), SWUSA (P=0.6111) and shellthickness (P=0.6663) during the entire experimental period. At 70 weeks of age large particleslimestone resulted in a significant higher tibia bone breaking strength (P=0.0107) and stress (P=0.0391). No significant (P>0.05) influence of limestone particle size was found on bonelength, width, weight, percentage ash and index at week 70 of age.The results of the second study illustrated that different ratios of small and large limestoneparticles had no significant effect on feed intake (P=0.4066), body weight (P=0.8908), eggproduction (P=0.2713), egg output (P=0.1457) and feed conversion ratio (P=0.2635) during theentire experimental period. No statistical differences were detected due to a mixture of differentratios of coarse and fine limestone particles on mean eggshell characteristics such as shellweight (P=0.6902), percentage egg shell (P=0.7297), eggshell calcium (P=0.6903), egg surfacearea (P=0.4474), SWUSA (P=0.7738) and eggshell thickness (P=0.7167) during the entireexperimental period.It was concluded that the different limestone particle sizes and ratios of small and large particleslimestone in the diets used during the present study, generally had no significant influence onbone and eggshell quality characteristics of Lohmann-Silver laying hens during the later stagesof lay, except on bone mechanical properties.

[发布机构] University of the Free State